Handbook c4 chemical reactions

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Agastya International Foundation

Chemical Reactions Handbook C4

I was taught that the way of progress was neither swift nor easy.

-Marie Curie (1867-1934) [Type text]

Handbook C4 Chemical Reactions OVERVIEW OF HANDBOOK ABL

CONCEPT Physical and chemical changes

ABL1

NO OF ACTIVITIES

TIME min

PAGE NO

1

50

4

ABL2

Chemical changes

3

45

13

ABL3

Chemical equations

3

55

22

ABL4

Types of reactions

5

60

33

ABL5

Endothermic and exothermic reactions

2

50

52

ABL6

Reversible and irreversible reactions

3

60

60

ABLs WITH REFERENCE TO STANDARD SERIAL NUMBER 1 2 3 4 5 6

STANDARD 8,9 8,9 8,9 8,9 8,9 8,9

RELEVANT ABL ABL1 ABL2 ABL3 ABL4 ABL5 ABL6

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LIST OF FIGURES, CHARTS AND WORKSHEETS S. No Figure 1 Figure 2 Chart 1 Chart 2 Figure 3 Worksheet 1 Worksheet 2 Worksheet 3 Worksheet 4 Worksheet 5 Worksheet 6 Worksheet 7 Worksheet 8 Worksheet 9 Worksheet 10

Name Baking soda experiment setup Copper sulfate reaction Basic symbols Types of reactions Ammonium dichromate experiment Chemical reactions observation sheet 1 Chemical reactions observation sheet 2 List of chemical changes in daily life Mind map worksheet List of chemical reactions taking place in and around us Coefficients and subscripts Chemical reactions observation sheet 3 Balancing equations Chemical reactions observation sheet 4 Observation sheet 5

Page No 26 56 25 33 61 7 15 15 17 17 22 25 27 52 54

Note to Instructor: All the figures in this handbook are for the Instructor’s reference only. The Charts need to be printed and shown to the learners during the course of the activity. Worksheets need to be printed out in advance for the students. The number of worksheets required is mentioned in the Material List.

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Activity

Learning objective

Key messages

1–

Time (min)

1.1

What is a physical change?

 

1.2

What is a chemical change?

   

15 Physical change is a temporary change Physical properties of the substance are altered No new substance is formed 35 Chemical change is a permanent change Change in composition takes place One or more new substances are formed

Physical and Chemical Changes

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ABL

Time: 15 min

ABL 1.1 LEARNING OBJECTIVE – What is a physical change?

Note to Instructor– This activity shows that substances can be changed in many ways and introduces students to how we can identify a physical change.

ADVANCE PREPARATION Material List Material 1. A 5 g piece of candle wax

Number Required 1 per classroom

2. China dish

1 per classroom

3. Spirit lamp

1 per class

4. Tripod stand

1 per class

5. Wire gauze

1 per class

6. A pair of Tongs

1 per class

7. Matchbox

1 per class

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Things to do Set up the tripod over the spirit lamp and place the wire gauze on the tripod. Place the wax in the china dish and place the china dish on the wire gauze. Place the experimental set up in a place where the students can observe from a safe distance.

Safety Precautions Tell the students that they should not touch any of the experimental materials

SESSION Link to known information/previous activity Not Applicable Procedure Divide the class into groups of 4-5. Turn on the spirit lamp and gently heat the wax in the china dish.

Use the tongs to hold the china dish while heating. Display the melted wax to the students and then set the china dish aside, away from the students, and allow it to cool. Show this to the students after a few minutes, when the wax starts becoming solid again.

UNDERSTANDING THE ACTIVITY Leading questions 1) 2) 3) 4)

What does the piece of wax look like?

What happened when we heated the wax?

What happened when we cooled the liquid?

Were the physical properties of the cooled wax the same as the physical properties of the candle piece?

5) Was there any new substance formed after the wax was melted and then cooled?

6) What is such a change called?

7) Is a physical change reversible?

8) Can you give examples of some physical changes that you have come across in your daily life?

9) Cutting and tearing of a substance is not reversible, how is it a physical change?

10) How is drying of clothes a physical change?

11) How is stretching of a rubber band a physical change?

12) How is dissolving salt/sugar in water a physical change?

Discussion and Explanation 1) Wax looks white in colour; it is solid and has the cylindrical shape of a candle.

2) When we heated the wax, it became liquid. It started to lose its shape and it became colorless.

3) When we cooled the wax, it again looked white and was solid. But its shape changed to the shape of the inside of the china dish.

4) The shape of the cooled wax was different from the shape of the original wax. All other physical properties were the same.

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5) No new substance is formed; if the cooled wax in the china dish was formed into a candle, it would burn just like the original candle 6) A change in one or more of the following properties - the physical state, shape and colour of a substance - is called a physical change.

7) On heating, the wax turned from solid to liquid. Again on cooling, it became solid again. A physical change is a temporary, reversible change.

8) Boiling of water, drying clothes, stretching a rubber band, tearing of paper, cutting of cloth, dissolving salt/sugar in water etc are examples of physical change.

9) Cutting and tearing result in the making the substance smaller – however, the substance remains the same.

10) On drying clothes, water is lost in the form of water vapour. The cloth is still the same and water is in the form of water vapour.

11) Stretching a rubber band increases its size, but nothing happens to its internal composition. When you stop stretching the rubber band, it returns to its original shape and size.

12) Once salt (or sugar) is dissolved in water, it loses its physical state and crystalline shape. However, if the salt solution is evaporated, salt crystals are recovered.

KEY MESSAGES   

Physical change is a temporary change Physical properties of the substance are altered No new substance is formed

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

TRY IT YOURSELF Look for simple examples of physical changes in your daily life and discuss with your teacher and classmates

Time: 35 min

ABL 1.2 LEARNING OBJECTIVE –What is a chemical change?

Note to Instructor– Here we talk about chemical changes. Stress is given on the chemical combining or breaking down of substances. We will also be using the observations on the wax melting to compare physical and chemical changes.

ADVANCE PREPARATION Material List Material

Number Required

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1.

5g sulphur

1 per class

2.

1 tsp sugar

1 per class

3.

5cm magnesium strip

1 per class

4.

1 spatula

1 per class

5.

1 china dish

1 per class

6.

1 spirit lamp

1 per class

7.

1 tripod stand

1 per class

8.

1 wire gauze

1 per class

9.

1 spirit lamp

1 per class

10.

1 matchbox

1 per class

11.

test tube holders

1 per class

12.

Deflagrating spoon

1 per class

13.

Gas jar

1 per class

14.

Hibiscus or any colored flower

1 per class

15.

Beaker/glass cup

1 per class

16.

Sandpaper

1 per class

17.

Spoon

1 per class

18.

1 pair of safety gloves

1 per class

19.

1 pair of safety goggles

1 per class

20.

Matchbox

1 per class

21.

Activity Cards

1 per group

Chemical Reactions Activity Cards.docx

22.

Chemical Reactions – Observation Sheet -1

1 per learner

Chemical Reactions Observation Sheet 1.docx

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Things to do Set up the tripod over the spirit lamp and place the wire gauze on the tripod. Place the experimental set up in a place where the students can observe from a safe distance. Make sure to remove any salts/dust formed on the magnesium tape using sand paper. Print the activity cards for Procedure-4.

Safety Precautions Tell the students to keep a safe distance and not to touch any of the materials or apparatus used in the experiment.Ask them to not touch the molten wax or look directly at the burning magnesium strip.

SESSION Link to known information/previous activity We have learnt about physical changes. Now let us learn about chemical changes.

Procedure 1 - Sulphur Take a clean gas jar, place a coloured flower inside the gas jar.Take small amount of sulphur powder in a deflagrating spoon. Introduce the sulphur inside the gas jar containing the flower. Ask the students to observe the gas jar carefully and write down their observations.

Now remove the spoon from the gas jar and light the sulphurwith the spirit lamp.Sulphur starts burning, immediately. Again, introduce this burning sulphur inside the gas jar containing coloured flower.Keep this undisturbed. Ask the students to observe the gas jar carefully and write their observations.

UNDERSTANDING THE ACTIVITY-1 Leading questions -1 1) What does sulphur look like at first?

2) What happens to the colour of the flower when we introduce the sulphur into the gas jar?

3) What happens to sulphur when we heat it?

4) What happens to the colour of the flower after we introduce the burning sulphur into the gas jar?

5) What happens after cooling the deflagrating spoon?

6) What could be the reason why we do not see sulphur in the deflagrating spoon after cooling?

7) How can you be sure that new substances have been formed?

8) How are the properties of the new product formed (sulphur dioxide) different from the properties of the sulphur?

9) What is such a change called?

10) What are some of the chemical changes you might have come across in your daily life?

Discussion and Explanation-1 1) Sulphur is a pale yellow, powdery, crystalline substance 2) There is no change in the colour of the flower 3) Sulphur turns into a liquid and releases a lot of smoke/fumes 4) The colour of the flower fades, probably because of the smoke/fumes released 5) After cooling the deflagrating spoon, we see a black residue. Sulphur does not re-form Agastya International Foundation. For Internal Circulation only.

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6) Sulphur goes through an irreversible, permanent change after heating and new products are formed. This is why we do not see sulphur re-form in the deflagrating spoon after cooling 7) When we burn sulphur, we observed fumes coming out. These fumes are sulphur dioxide which was not present before burning the sulphur 8) When we expose the coloured flower to sulphur powder, the colour of the flower does not change.

When the same flower is exposed to sulphur dioxide, its colour changes. The properties of the new substances formed are therefore different from the properties of the original substances 9) An irreversible, permanent change where one or more new substances are formed, with a lot of energy either given out or absorbed is called a chemical change. A chemical change is also called a chemical reaction.

10) Some examples of chemical change - Souring/curdling of milk; burning of paper, coal, wood; rusting of iron nails; ripening of fruits; change in colour of cut apple or brinjal etc Procedure 2 - Sugar Put half of the sugar in a small quantity of water and mix well. Boil the sugar and water mixture in a china dish until the solution becomes concentrated and the sugar starts to re-crystallize. Let the china dish cool for some time. Ask the students to observe the china dish carefully and write their observations. Take the other half of the sugar in the spatula and heat it over the spirit lamp. Keep the spoon aside for cooling. Ask the students to observe the spatula carefully and write their observations.

UNDERSTANDING THE ACTIVITY-2 Leading questions -2 1) What are the physical properties of sugar?

2) What happens to the sugar when it mixes with water?

3) What happens after the sugar solution in the china dish was boiled and cooled?

4) Does the sugar have the same colour and state as it had earlier?

5) What happens when sugar is heated in the spatula?

6) Which is the physical change and which is the chemical change?

Discussion and Explanation-2 1) Sugar is in the form of small crystals. It is solid and white in colour 2) Sugar dissolves in the water to form sugar solution 3) Sugar crystals start reforming as the solutions gets more concentrated and more crystals form after the solution in the china dish is cooled 4) Yes, the sugar looks the same as it did earlier. It has the same colour, state and shape 5) Sugar in the spatula slowly turns brown and then black. Water vapour fumes are seen and a black residue is left behind on the spatula 6) Dissolving sugar in water is a physical change. Heating sugar on the spatula is the chemical change Procedure 3 – Magnesium Ribbon Wear gloves and hold the magnesium strip. Cut the magnesium strip in half.Ask the students to observe and write their observations. Next, hold the magnesium strip with tongs and light it over the spirit lamp.

Drop the burnt ash into the dustbin filled with sand. Ask the students to observe and write their observations.

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UNDERSTANDING THE ACTIVITY-3 Leading questions -3 1) Did a new substance form when we cut the magnesium strip?

2) What happened to the magnesium tape when it was burnt?

3) What kind of change is this and why?

4) Did we get the magnesium strip back after it was burnt and why?

Discussion and Explanation-3 1) No, we got the same magnesium tape, but in a smaller size 2) Lots of smoke and light were emitted, and a white residue was left behind 3) A new substance is formed. It is a chemical change.

4) No, because this is a irreversible permanent change - a chemical change

Procedure 4 – Activity Cards Distribute the activity cards – one set for each group. Ask the students to separate and place the physical change cards on the right hand side and the chemical change cards on the left hand side.

UNDERSTANDING THE ACTIVITY-4 Leading Questions - 4 Not Applicable Discussion and Explanation-4 Collect the answers and discuss them according to the answer key given below (Answers for Instructor’s reference: Frying of egg, rusting of nails and burning of wood are all examples of chemical changes; Slicing of vegetables, boiling of water and melting of ice are all examples of physical changes)

KEY MESSAGES   

Chemical change is a permanent change Change in composition takes place One or more new substances are formed

LEARNING CHECK You can use the following questions either as a handout for an individual or group exercise or as a quiz to see how much has been understood. The answer key is available after the questions 1. Which of the following is an example of physical change? a. Mixing baking soda and vinegar together, and this causes bubbles and foam b. Breaking of a glass cup that falls from the table c. Lighting a piece of paper on fire and the paper burns up and leaves ashes d. Making a cup of tea for your mother 2. Which of the following is an example of chemical change?

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a. b. c. d.

Filling up a balloon with hot air Boiling water in a container Adding curds to warm milk Tearing up paper into small pieces

3. Which change can be easily be reversed? a. b. c. d.

Chemical Change Physical Change Both a physical and chemical change Neither a physical or chemical change

4. When a new substance is formed with different properties than the original substance it is called a: a. b. c. d.

Chemical change Physical change Freezing Boiling

5. If the chemical properties of a substance remain unchanged and onlythe appearance, physical state or shape of a substance changes it is called a: a. b. c. d.

Chemical change Physical change Both a physical and chemical change Neither a physical or chemical change

6. Which is an example of a physical change? a. b. c. d.

Metal rusting Silver tarnishing Water boiling Paper burning

7. Which is an example of chemical change? a. b. c. d.

Water evaporates Wood is cut Bread is baked Wire is bent

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(Answers for Instructors reference:1.b, 2.c, 3.b, 4.a, 5.b, 6.c, 7.c)

WEB RESOURCES http://www.chem4kids.com/files/matter_chemphys.html http://chemwiki.ucdavis.edu/Analytical_Chemistry/Qualitative_Analysis/Chemical_Change_vs._Physical_C hange

ABL 2– Chemical Changes Activity

Learning objective

Key messages

Time (min)

2.1

How are new substances formed in a chemical change?

2.2

What are the signs of a chemical reaction?



20 Chemical changes are chemical reactions  A chemical reaction results in the transformation of one set of substances into another  Signs of a chemical reaction 15 include:

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  

2.3

What are the chemical reactions taking place around us in our daily life?

  



Formation of precipitate Appearance of bubbles Release of heat and light energy Noticeable odour Change in colour Chemical reactions take place in and around us. For example, in our bodies, in our surroundings like the kitchen, garden etc.

Chemistry is not limited to beakers and laboratories. It is all around us, and the better we know chemistry, the better we know our world.

10

Time: 20 min

ABL 2.1 LEARNING OBJECTIVE – How are new substances formed in a chemical change?

Note to Instructor–The concept of a chemical change as a chemical reaction is introduced here.

ADVANCE PREPARATION Material List Material 1. 5x5cm piece of paper

Number Required 1 per group

2. Matchbox

1 per group

3. Tongs

1 per group

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4. Spirit lamp

1 per group

5. Beaker filled with water

1 per group

Things to do Set up the spirit lamps and other material for each group at appropriate places in the classroom.

Safety Precautions Instruct the students to use care while handling the spirit lamp, tongs and burning paper. Only one student at a time should perform the experiment. All other learners in the group should stand a few steps away from the experimental setup. Long hair must be tied back. Paper has to be dropped into the beaker of water after burning.

SESSION Link to known information/previous activity Not Applicable Procedure Divide the class into groups of 5 learners. Assign an experimental set-up to each group and designate a person in each group who will perform the experiment and another person who will assist. Ask each group to light the spirit lamp. Next ask them to pick up a piece of paper using tongs and set it alight using the spirit lamp. Observe the paper as it is burning. After burning the paper, drop the ashes in the beaker of water. Discuss what happened during and after the burning of the paper.

UNDERSTANDING THE ACTIVITY Leading questions 1) What happened as the paper was burning?

2) What did you get after burning the paper?

3) What helps the paper to burn?

4) Is the burning of the paper a physical change or a chemical change?

5) Why do you think that burning of paper is a chemical change?

6) Why is a chemical change, also called a chemical reaction?

7) What are the reactants in this chemical reaction?

8) What are the products of this chemical reaction?

Discussion and Explanation 1) A lot of smoke, heat, fire and light were released 2) We get ashes of paper 3) Oxygen in the air helps the paper to burn 4) The burning of the paper is a chemical change or a chemical reaction 5) In a chemical change, new substances are formed. Paper, the original substance, is converted into ash and smoke, which are new substances. Also this is an irreversible, permanent change – ash cannot be converted into paper Agastya International Foundation. For Internal Circulation only.

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6) A chemical reaction is a chemical change where new products are formed. In a chemical reaction, two or more substances called reactantsinteract to create new substances called products.

7) Paper and oxygen are the two reactants 8) Ash and smoke are the two main products along with carbon dioxide

KEY MESSAGES  

Chemical changes are chemical reactions A chemical reaction is the transformation of one set of substances into another

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 15 min

ABL 2.2 LEARNING OBJECTIVE – What are the indicators of a chemical reaction?

Note to Instructor –The different signs that a chemical reaction is taking place are explained here.

ADVANCE PREPARATION Material List 1.

Material 1 container of 5ml vinegar

Number Required 1 per group

2.

2 containers of 5g baking soda

1 per group

3.

5 ml calcium chloride solution

1 per group

4.

2 ml iodine solution

1 per group

5.

5 g starch powder

1 per group

6.

3 droppers

1 per group

7.

4 plastic cups/test tubes

1 per group

8.

4 pencils

1 per group

9.

4 wipe cloths/paper napkins

1 per group

10.

Observation Sheet 2

1 per learner

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11.

List of chemical changes in daily life for ABL 2.3 for Instructor use

1 per class

Things to do Print required copies of Observation sheet 2.

Safety Precautions Tell the learners to keep the substances away from their clothes, eyes and mouth. Use safety goggles if available.

SESSION Link to known information/previous activity We have learnt that a chemical reaction results in the creation of new substances. But how do we know that a chemical reaction has occurred? Let us learn about the indicators of a chemical reaction or a chemical change.

Procedure Divide the learners into 5 groups. Distribute the material among the groups. Each learner in the group can take turns in performing the activity.At each stage ask the learners to observe the changes and to record the observations in the observation sheet.

First take a small quantity of baking soda in the plastic cup and add a few drops of vinegar to this using a dropper. Second, ask the learners to take a small quantity of baking soda in a fresh plastic cup and add a few drops of calcium chloride solution to it. Third, ask the learners to take a small quantity of starch in a fresh plastic cup and add a few drops of iodine to it.

UNDERSTANDING THE ACTIVITY Leading questions 1) What happens when the vinegar and baking soda are mixed?

2) Why do you think fizz with bubbles isreleased?

3) What is this an indicator of?

4) What happens when calcium chloride and baking soda are mixed?

5) What do you think is the white solid?

6) How do you know that this is a new substance?

7) What happens when starch and iodine are mixed?

8) What does the purple colour indicate?

Discussion and Explanation 1) We observe fizzing with bubbles coming out. The plastic container feels cold.

2) Gas may have been released 3) Fizzing, bubbling and a change in temperature are all indicator of a chemical reaction 4) We observe fizzing with bubbles. The plastic cup feels warm – some heat has been generated. After some time, there is a white solid substance formed at the bottom of the container called a precipitate 5) The white solid must be a new substance that has formed Agastya International Foundation. For Internal Circulation only.

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6) Since there was fizzing and bubbling, a chemical reaction must have taken place. This is how we know that new substances have formed. The new substance is calcium carbonate 7) A new dark purple substance is formed.

8) The purple colour indicates that a chemical reaction has occurred. Iodine is brown in colour and starch is white. The formation of a dark purple substance means that a new substance has been formed. A change in colour is often but not always, an indicator of a chemical reaction

KEY MESSAGES 

Signs of a chemical reaction include the following: o Formation of precipitate o Appearance of bubbles o Release of heat and light energy o Noticeable odour o Change in colour

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

TRY IT YOURSELF Kitchen Science: Add half a cup of plain water to 2 teaspoons of baking soda. Did you observe any changes? Now, add half a cup of lemon juice to 2 teaspoons of baking soda. What happens? Is this a chemical reaction?

Time: 25 min

ABL 2.3 LEARNING OBJECTIVE – What are the chemical reactions taking place around us in our daily life?

Note to Instructor –The learners use mind mapping techniques to explore the common chemical reactions in our daily life

ADVANCE PREPARATION Material List 1

Material Mind map worksheet

Number Required 1 per group

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Mind_Map_Template. pdf 1

2 3

Pencils/pens List of chemical reactions taking place in and around us

1 per group 1 per class

Things to do Print out the mind map template worksheet.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We now know about chemical changes and chemical reactions. Did you know that chemical reactions are going around us in our daily life? Let us learn more about these reactions.

Procedure Divide the learners into 4 groups. Distribute the Mindmap template worksheet to each group. Learners in each group will take turns to write on the worksheet. Explain to the learners that they will be thinking of examples of chemical reactions around us. They will be doing this in a group and writing out all the examples. Tell them to write down an area or sphere of daily life in the centre – such as “Kitchen” or “School” or “Garden” etc. They will enter all the chemical reactions that they see in this area. For example in the “Kitchen” group they will enter “Curdling”, “Fermentation” etc. Discuss on the ideas generated by each group.

UNDERSTANDING THE ACTIVITY Leading questions 1) Why do you think this is a chemical reaction?

Discussion and Explanation 1) This is a chemical reaction because…  You can use the list below to give the learners a few examples of the chemical reactions occurring in and around us: PLACE REACTION Society festivals

1

Fireworks/firecrackers are a result of chemical reactions. They contain a mixture of potassium nitrate, charcoal and water which react together to burn and produce gaseous products. Because this mixture is inside a paper covering, the gasses build up pressure inside which leads to an explosion.

http://www.mymindmap.net/pdf/Mind_Map_Template_Mulit_Nodes.pdf

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Did you know that the biggest firecracker ever made was in Japan and weighed 700 Kg. It was as big as a cow! kitchen

Matchsticks catch fire due to a chemical reaction between potassium chlorate on the stick and phosphorous on the strip. They react to produce a large amount of heat which leads to fire.

outdoors

Think of the dry wood in the fireplace. When we light the wood up, it burns gently and after a while it turns into ashes. As it burns, it produces heat, light and smoke which escapes through the chimney. The heat, light, fire and smoke are all good characteristics of a chemical reaction, which result in a completely new matter—ashes.

home

Window grills made up of iron show a browning coat of rust due to the formation of iron oxide as a result of the reaction between iron and oxygen in the presence of water vapour from the air.

Our body

Digestion – when you eat food, reactions happen between substances secreted by your body (like enzymes and acids) and the food so that your food can breakdown to give you nutrients and energy.

Bathrooms and kitchens

All cleaning agents have chemicals that have complex chemicals reactions with the dirt so that it can be easily removed as a product. Examples of these chemicals are window cleaner (which contains the corrosive and poisonous chemical ammonia), bleach, and drain cleaner.

Soda bottle

When we leave a coke bottle or any fizz drink open it loses its fizz. This is because the carbonic acid (fizz) decomposes into carbon dioxide and water.

Basically, you will lose the bubbles from your drink.

Our body

Do you know indulging in physical movements is associated with a chemical reaction? The process requires energy, which is yielded by aerobic respiration.

Over here, respiration helps breaks down glucose (an energy source) into water, carbon dioxide and energy in form of ATP (adenosine triphosphate). The balanced cellular respiration equation is represented as: C6H12O6 + 6O2→ 6CO2+ 6H2O + Energy (36 ATPs)

Plant body in a garden

Photosynthesis is the process by which green plants manufacture their own food. This occurs in presence of sunlight and other raw materials, namely carbon dioxide and water. The chlorophyll pigment harvests the light energy from sunlight, which is then converted into glucose by the phenomenon of photosynthesis. In short, it is the opposite of aerobic respiration. The equation

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for photosynthesis is: 6CO2+ 6H2O + Light energy → C6H12O6 + 6O2

KEY MESSAGES  

Chemical reactions take place in and around us. For example, in our bodies, in our surroundings like the kitchen, garden etc.

Chemistry is not limited to beakers and laboratories. It is all around us, and the better we know chemistry, the better we know our world.

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

WEB RESOURCES http://www-tc.pbskids.org/fetch/parentsteachers/activities/pdf/FETCH_TempestInATeacup_AG.pdf http://www.middleschoolchemistry.com/lessonplans/chapter6/lesson7

ADDITIONAL INFORMATION FOR INSTRUCTOR How to judge the indicators of chemical change? (For Instructor clarification) Change in Temperature A change in temperature is characteristic of a chemical change. During an experiment, one could dip a thermometer into a beaker to verify a temperature change. If temperature increases (or decreases), a chemical change is likely to be occurring. This is different from the physical temperature change. During a physical temperature change, one substance, such as water is being heated. In the case of a chemical reaction, one compound is mixed in with another, and these reactants produce a product. When the reactants are mixed, the temperature change caused by the reaction is an indicator of a chemical change.

Change in Color A change in color is also another characteristic of a chemical reaction taking place. For example, if one were to observe the rusting of metal over time, one would realise that the metal has changed color and turned orange. This change in color is evidence of a chemical reaction. However, one must be careful; sometimes a change in color is simply the mixing of two colors, but no real change in the composition of the substances

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Noticeable Odor When two or more compounds or elements are mixed and a scent or odor is present, a chemical reaction has taken place. For example, when an egg begins to smell, (a rotten egg) a chemical reaction has taken place. This is the result of a chemical decomposition.

Formation of a Precipitate The formation of a precipitate may be one of the most common signs of a chemical reaction taking place. A precipitate is defined to be a solid that forms inside of a solution or another solid. Precipitates should not be confused with suspensions, which are solutions that are homogeneous fluids with particles floating about in them. For instance, when a soluble carbonate reacts with Barium, a Barium Carbonate precipitate can be observed.

Formation of Bubbles and Fizzing The formation of bubbles, or rather a gas, is another indicator of a chemical reaction taking place. When bubbles form, a temperature change could also be taking place. Temperature change and formation of bubbles often occur together.

Mind Mapping A mind map is a diagram used to visually outline information. It can be used during a brainstorming session to organize and explore ideas. A mind map is often created around a single word or text, placed in the centre, to which associated ideas, words and concepts are added. Major categories radiate from a central node, and lesser categories are sub-branches of larger branches.Categories can represent words, ideas, tasks, or other items related to a central key word or idea.

ABL 3– Chemical Equations the Language of Chemistry (For classes 9 & 10 only) Activity

Learning objective

Key messages

Time (min)

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3.1

What are the basic symbols, coefficients and subscripts in a chemical equation?



 





3.2

What is the law of conservation of mass?



3.3

What is a balanced equation?



20 A chemical equation is a short and clear way of expressing a chemical reaction Symbols helps to represent chemical equations A coefficient is a whole number that appears before a formula in a chemical equation Subscript is a part of the chemical formula that indicates the number of atoms of the preceding element Using the coefficients and subscripts in a formula, we can calculate the number of atoms of the substance When matter goes through 15 a physical or chemical change, the amount of matter stays the same before and after the changes occur 20 A chemical equation in which the number of atoms of specific element is the same on both sides of the equation

Time: 20 min

ABL 3.1 LEARNING OBJECTIVE – What are the basic symbols, coefficients and subscripts in a chemical equation?

ADVANCE PREPARATION Material List Material 1. 1 Large size Basic Symbols Chart

Number Required 1 per class

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2

2. 1 set of Chemical symbol flashcards

1 per group

Chemical Reactions Basic Symbols Flashcard.docx

3. Coefficients and Subscripts worksheet

1 per learner

Chemical ReactionsCoefficients & Subscripts Work Sheet.docx

Things to do Print out the chart, flashcards and worksheets. Cut out each set of flashcards from the sheets and shuffle each set.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We have learnt about chemical reactions. Let us now see how chemical reactions can be represented.

Procedure - 1 Divide the learners into groups of 5. Display the Basic Symbols Chart in a prominent location that it visible to the learners. Explain the basic symbols to the learners as applicable. Now remove the chart.

Distribute the two sets of basic symbol flashcards to each group. Ask them to match the cards in set 1 (symbols) to the cards in set 2 (explanations).

UNDERSTANDING THE ACTIVITY Leading questions-1 1) Have you seen other symbols in your day-to-day life? Where have you see them?

2) What do these symbols mean?

3) Why are these symbols used?

4) Can you think of why we need symbols for chemical reactions?

Discussion and Explanation-1 1) Yes, on trucks, symbols for traffic, hospitals etc 2) Symbols have different meaning such as “Stop”, “Don’t Smoke”, “No Horn” etc 2http://www.docstoc.com/docs/21607758/Symbols-used-in-Chemical-Equations

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3) Symbols are shorthand for long explanations. They save space and are easy to understand 4) The names of the reactants and products are very long, also there is a lot of information about the reaction such as, whether the reactants are solid or liquid, whether heat is give out or taken in etc.

Symbols are shorthand for the long explanations.A chemical equation describes, in a shorthand way, what happens in a chemical reaction. The equation identifies the reactants and products, the formulas of the reactants and products, the phases of the reactants and products (solid, liquid, gas), and the amount of each substance.

Procedure - 2 Distribute the Subscripts and Coefficients Worksheet to each learner. Ask them to identify coefficients and subscripts in the worksheet.

UNDERSTANDING THE ACTIVITY Leading questions-2 1) Why do you think it is necessary to specify coefficients and subscripts?

Discussion and Explanation-2 1) The quantity of the product is dependent on the quantity of each reactant. It is, therefore, important to know the number of atoms of the reactants and products in a chemical equation.

KEY MESSAGES     

A chemical equation is a shorthand way of expressing a chemical reaction Symbols helps to represent chemical equations A coefficient is a whole number that appears before of a formula in a chemical equation Subscript is a part of the chemical formula that indicates the number of atoms of the preceding element Using the coefficients and subscripts in a formula, we can calculate the number of atoms of the substance

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 15 min

ABL 3.2 LEARNING OBJECTIVE – What is the law of conservation of mass?

Note to Instructor–The learners learn about chemical equations, basic symbols, coefficients and subscripts Agastya International Foundation. For Internal Circulation only.

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ADVANCE PREPARATION Material List Material

Number Required

1. 10ml Vinegar

1 per class

2. 2 tsp baking soda

1 per class

3. Measuring cylinder/jar

1 per class

4. 100 ml (or 125 ml) conical flask

1 per class

1. Small balloon to fit over the neck of the conical flask

1 per class

2. Plastic spoon

1 per class

3. Small funnel to fit the mouth of the balloon

1 per class

4. Electronic weighing machine

1 per class

5. Large print out of Observation Sheet 3

1 per class

6. Observation Sheet 3

1 per learner

Chemical Reactions Observation Sheet 3.docx

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Things to do Assemble the materials wherethey are visible to all learners. Print out the Observation Sheet 3. (There are 2 observation tables in every sheet – so print out half as many as you need) Stretch and inflate the balloon to make sure that there are no holes in it.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We have learnt about symbols and coefficients and subscripts. We know how to calculate the number of atoms of reactants and products. Now let us learn why exactly it is important to know these quantities.

Procedure Display the bigger version of the Observation Sheet 3 in a prominent location. Ask 2 learners to come and measure 50ml of vinegar into the conical flask. Next ask 2 different learners to measure 2tsp of baking soda into the balloon, using the funnel. Carefully fix the balloon onto the neck of the conical flask as shown in the picture. Make sure there are no leaks where gas can escape. Now, place the flask and balloon set-up on the weighing scale. Explain to the students that in everyday usage both words are used interchangeably, you will be using the term mass instead of weight. Ask 2 more learners to come and look at the reading for the mass of the apparatus. Ask them to make a note of it. Write this on the large Observation Sheet 3 and ask all the learners to write this down. Call on two more different learners to come and carefully lift the deflated balloon in such a way that the baking soda in the balloon falls into the vinegar. Ask the learners to observe the changes and note these down in their Observation Sheets. Call on 1 or t learners to read out their observations. Note down these observations, if correct, on the large Observation Sheet 3.Now call on two more learners to take the reading for the mass of the apparatus after the reaction for the closed balloon set-up. Now remove the balloon and allow the gas to escape. Call on two more learners to take the reading of the open balloon set-up. Note down all readings on the large Observation Sheet 3.

Write the equation for the reaction on the board: Baking Soda + Vinegar -> Sodium Acetate+ Water + Carbon Dioxide NaHCO3 + CH3COOH ->CH3COONa + H20 + CO2 Sodium Bicarbonate + Acetic Acid -> Sodium acetate + Water + Carbon dioxide

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Figure 1 – Baking soda experimental set up.

UNDERSTANDING THE ACTIVITY Leading questions 1) What are the products and reactants in this reaction?

2) What was the mass of the closed balloon set-up before the reaction?

3) What happened when the vinegar and baking soda combined?

4) Why does the balloon get inflated?

5) What were the signs/indicators that a chemical reaction took place?

6) What was the weight of the closed balloon set-up after the reaction? Is it the same or different as the reading before the reaction and why?

7) What was the mass of the open balloon set-up after the reaction? Is it the same or different as the reading for the closed set-up and why?

8) What happens if we increase or decrease the quantity of the reactants? Will the law be the same?

Discussion and Explanation 1) The reactants are vinegar and baking soda and the products are sodium acetate, water and carbon dioxide 2) The mass of the closed balloon set-up before the reaction is ________ 3) We see fizzing and bubbling. After a while, the balloon gets inflated 4) The balloon probably gets inflated because carbon dioxide is generated. Since there is no place for the gas to escape, it inflates the balloon 5) Fizzing an bubbling are indicators that a chemical reaction is taking place 6) The mass of the closed balloon set-up after the reaction is ________. It is the same as the reading we took before the reaction. This is because of the law of conservation of mass. According to this law, when matter undergoes a physical or chemical change, the amount of matter stays same before and after the changes. This means that in a chemical reaction, atoms are neither created nor destroyed. All atoms present in the reactants are also present in the products.

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7) The mass of the open balloon set-up after the reaction is ________. It is less than the mass of the closed set-up probably because gas escapes from the balloon.

8) If we increase or decrease quantity of reactants, quantity of products also increases or decreases.

The law is still the same.

KEY MESSAGES 

When matter goes through a physical or chemical change, the amount of matter stays the same before and after the changes occur

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 20 min

ABL 3.3 LEARNING OBJECTIVE – What is a balanced equation?

Note to Instructor–The learners learn about balancing chemical equations

ADVANCE PREPARATION Material List Material 1. 5 Chart papers – green, yellow, orange, blue, red,

Number Required 1 per group

brown

2. Sketch pens

1 per group

3. Balancing Equations Worksheet

1 per learner

Chemical Reactions Balancing Equations Worksheet.docx

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Things to do Prepare the cards or discs as per the table. For each group, provide a set of cardboard discs or cards for the 6 elements as shown.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We have learnt about the law of conservation of mass. Now let us learn why it is important to balance equation and how to do it.

Procedure-1 Form 5 groups.Provide each group with the rules/suggestions sheets for balancing equations. Explain the rules and suggestion with the example on the board. Once the students are clear, facilitate the group activity. Distribute 1 set of cardboard discs to each group. Explain that they will be using the disc as you explain. Tell them that each disc represents one atom of the substance. Remind them about coefficients and subscripts.

Write the following unbalanced equation on board and lead the following questions H2 + O2

H2O

UNDERSTANDING THE ACTIVITY Leading questions -1 1) Is this a balanced equation? Why or why not?

2) How many hydrogen discs are on the left side of the arrow?

3) Why should the equation be balanced?

4) How do we balance an equation?

5) How do we balance the equation on the board?

Discussion and Explanation-

Atom:

O

H

Na

CI

K

Ca

Colour of card or disc:

Green

Yellow

Orange

Blue

Red

Brown

12

8

4

4

4

2

Number of card or disc

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1) This is not a balanced equation, because there are 2 atoms of hydrogen and 2 atoms of oxygen on the left side of the arrow, but there are only 2 atoms of hydrogen and 1 atom of oxygen on the right side 2) There are 2 hydrogen atoms on the left side of the arrow; therefore there should be 2 hydrogen discs 3) According to the law of conservation of mass, the number of atoms of reactants should be equal to the number of atoms of the product. That is why it is necessary to balance the equation 4) Count the number of atoms of each element in the reactants and products. Balance the elements one at a time by using coefficients. When no coefficient is written it is assumed to be a 1. It is best to begin with an element other than hydrogen or oxygen. These two elements often occur more than twice in an equation. You must not attempt to balance an equation by changing the subscripts in the chemical formula of a substance 5) In the equation on the board, hydrogen is balanced, but oxygen is not. If we put a coefficient 2 in front of H2O then oxygen gets balanced: (write on board) H2+O2 2H2O But now there are twice as many hydrogen atoms in the product as there are in the reactants. To correct this, put a coefficient of 2 in front of H2. Now the atoms in the product are equal to the number of atoms in the reactants

Procedure -2 Distribute the Balancing Equations Worksheet to all learners. Ask them to fill in the blanks to balance the 3 reactions.

Leading questions -2 Not Applicable Discussion and Explanation-2 Not Applicable

KEY MESSAGES 

A chemical equation in which the number of atoms of one type is the same on both sides of the equation

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

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INTERESTING INFORMATION During the 1780s the French chemist Antoine Lavoisier showed that matter can never be created or destroyed in a chemical reaction. Lavoisier emphasized the importance of making very careful measurements in his experiments. Because of his methods, he was able to show that reactions that seem to gain mass or lose mass actually involve reactions with gases in the air. These gases could not be seen, but their masses could be measured.

An example of Lavoisier’s work is his study of the reaction of the metal mercury when heated in air. In this reaction, the reddish orange product formed has more mass than the original metal. Lavoisier placed some mercury in a jar, sealed the jar, and recorded the total mass of the setup. After the mercury had been heated in the jar, the total mass of the jar and its contents had not changed. Lavoisier showed that the air left in the jar would no longer support burning—a candle flame was snuffed out by this air. He concluded that a gas in the air, which he called oxygen, had combined with the mercury to form the new product.

Lavoisier conducted many experiments of this type and found in all cases that the mass of the reactants is equal to the mass of the products. This conclusion, called the law of conservation of mass, states that in a chemical reaction atoms are neither created nor destroyed. All atoms present in the reactants are also present in the products

WEB RESOURCES http://www.docstoc.com/docs/21607758/Symbols-used-in-Chemical-Equations http://classes.kvcc.edu/chemistry100/Lab01/Lab01_procedure.htm http://www.middleschoolscience.com/conservation-of-mass-isn.pdf

ADDITIONAL INFORMATION FOR INSTRUCTOR Balancing equation using mathematics (only for Instructors) Another way of balancing equation is to mathematically solve them as linear system of equation Equation: H2 + O2

H2O

Process: A. First, place letter coefficients in front of each term: aH2 + bO2 ---> cH2O B. Now, use each element to produce an equation involving the coefficient letters:

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Hydrogen: 2a + 0b = 2c Oxygen: 0a + 2b = 1c C. Next, use math to solve this system of equations: 2a=2c implies a=c 2b=c implies b=1/2 c D. Now, choose any integer value for c (since we would like the smallest integral solutions, c=2 works well).

E. If c=2; then a=2 also; and b=1/2 c =(1/2)(2) =1 Thus, as before 2H2 + 1O2 ----> 2H2O Equation 2 C2H6O + O2 -----> CO2 + H2O Process A. Coefficients: aC2H6O + bO2 -----> cCO2 + dH2O B. Equations: C: 2a + 0b = 1c + 0d H: 6a + 0b = 0c + 2d O: 1a + 2b = 2c + 1d C. Solve in terms of any letter. In this case, "a" may work best since it is represented in each equation: c=2a 2d=6a implies d=3a 2c+d-2b=a by substitution: 2(2a) + 3a -2b =a implies 7a -2b =a which implies: -2b = -6a implies b=3a Therefore: b=3a; c=2a; and d=3a D. Now let "a" be any integer (1 works well when no fractions are involved).

Thus, a=1; b=3; c=2; and d=3 and consequently E. 1C2H6O + 3 O2 -----> 2CO2 + 3H2O Activity: Use the mathematical method to balance the equations below 1. Zn + HCl ----> ZnCl2 + H2 2. Al + O2 -----> Al2O3 3. Al + CuSO4 ------> Al2(SO4)3 + Cu Agastya International Foundation. For Internal Circulation only.

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4. Li + H2O ------> LiOH + H2

ABL 4– Types of Reactions Activity

Learning objective

Key messages

Time (min)

What are the four types of chemical reactions?



4.2

What is a combination reaction?

4.3

4.1

Chemical reactions can be classified into: Combination Decomposition Single displacement Double displacement

10



A combination reaction is a reaction where two reactants combine to form one product

15

What is a decomposition reaction



10

4.4

What is a single displacement reaction?



A decomposition reactionis a reaction in which a single compound splits into two or more simple substances under suitable conditions Single Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound

4.5

What is a double displacement reaction?



A double displacement reactionis a chemical reaction in which an element from each of the reactants displaces the other to form new compounds

10

   

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15

Time: 10 min

ABL 4.1 LEARNING OBJECTIVE – What are the four types of chemical reactions?

Note to Instructor– An introduction to the basic types of chemical reactions using movement and action.

ADVANCE PREPARATION Material List Material 1 Large size Reactions Type Chart

Number Required 1 per class

Chemical Reactions Reactions Chart.docx

Things to do Print out the Reactions Chart.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We have learnt about chemical reactions; now let us look at the different types of chemical reactions.

Procedure Divide the class into 4 groups. Display the Types of Reactions Chart and explain the different types of reactions to them. Explain to them that they will be enacting the different types of reactions. Pick students randomly from the different groups and ensure that there are no repeats.

Combination Reaction: Ask 2 students to stand at different ends of the classroom and walk towards each other. They come together and stand next to each other. Point out the combination reaction on the chart.

Decomposition Reaction: Call on 2 students to stand next to each other. They then leave and move to other ends of the class. Point out the decomposition reaction on the chart.

Single Displacement Reaction: Call on 2 students to stand next to each other. One student moves to the other end of the class while a third student takes the place of the second one near the first student.

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Double Displacement reaction: Two students stand together in the middles of the group, both are displaced by two more students

UNDERSTANDING THE ACTIVITY Leading questions 1) 2) 3) 4)

What do you understand by a combination reaction?

What do you understand by a decomposition reaction?

What do you understand by a single displacement reaction?

What do you understand by a double displacement reaction?

Discussion and Explanation 1) This type of reaction is when a metal in its elemental state combines with a non-metal in its elemental state to form a compound. We are already aware that elements are broadly divided into metals and non-metals and most of the time, a metal always reacts with a non-metal to give rise to a compound.

2) This type of reaction is when a compound composed of metal and a non metal breaks up into the metal and non-metal each in their elemental state 3) In this type of reaction, a compound composed of a metal and a non-metal interacts with a metal or a non-metal and forms a new compound and the other is left in its elemental state 4) In this type of reaction, two compounds composed of a metal and a non metal interact and two new compounds are created

KEY MESSAGES 

Chemical reactions can be classified into: o Combination o Decomposition o Single displacement o Double displacement

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 15 min

ABL 4.2 LEARNING OBJECTIVE – What is a combination reaction?

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Note to Instructor– This activity is an example of a combination reaction. The experiment is the combustion of magnesium. If it has already been performed in a previous ABL, there is no need to repeat it here.

ADVANCE PREPARATION

Material List 1) Material

1 2 3 4 5 6 7

Number Required

7.

5cm magnesium strip

1 per class

1 spirit lamp 1 matchbox Tongs/test tube holders Sandpaper 1 pair of safety gloves 1 set of safety goggles Dustbin filled with sand

1 per class 1 per class 1 per class 1 per class 1 per class 1 per class 1 per class

Things to do Place the experimental set up in a place where the students can observe from a safe distance. Make sure to remove any salts/dust formed on the magnesium tape using sand paper.

Safety Precautions Tell the students to keep a safe distance and not to touch any of the materials or apparatus used in the experiment. Ask them to not to look directly at the burning magnesium strip.

SESSION Link to known information/previous activity We learnt about different types of chemical reactions in the previous activity. Here we will look at an example of a combination reaction.

Procedure Wear gloves and hold the magnesium strip. Cut the magnesium strip in half. Next, hold the magnesium strip with tongs and light it over the spirit lamp. Drop the burnt ash into a dustbin filled with sand.

UNDERSTANDING THE ACTIVITY Leading questions 1) What happened to the magnesium tape when it was burnt?

2) How many reactants were there? What were they?

3) How many products were there?

4) How did the reactants combine and what was the product?

5) What is this type of reaction called?

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6) Why was heat and light emitted during this reaction?

Discussion and Explanation 1) Lots of smoke and light were emitted, and a white residue was left behind 2) There were 2 reactants, magnesium and air 3) There was 1 product – the white residue that was formed 4) Magnesium and oxygen in the air combine to form magnesium oxide 2Mg(s) + O2(g) 2MgO(s) 5) This type of reaction is a combination or synthesis reaction becausein these reactions new substances are created or synthesized. This reaction is of the type: A + B AB. After the reaction there are no individual reactants left. Only one product is formed 6) Combination reactions involve the formation of new connections or bondsbetween the reactants to form the product. This process releases a large amount of energy in the form of heat and light.

KEY MESSAGES 

A combination reaction is a reaction where two reactants are combined to form one product

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 10 min

ABL 4.3 LEARNING OBJECTIVE – What is a decomposition reaction?

Note to Instructor– This activity explains the decomposition reaction, which is the opposite of a combination reaction.

ADVANCE PREPARATION Material List Material 1.

10g potassium permanganate

Number Required 1 per class

2.

1 dry boiling test tube

1 per class

3.

1 spatula

1 per class

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4.

1 beaker filled ž with water

1 per class

5.

1 spirit lamp

1 per class

6.

1 incense stick

1 per class

7.

1 test tube brush

1 per class

8.

1 matchbox

1 per class

9.

2 pairs safety gloves

1 per class

10.

2 pairs of safety goggles

1 per class

Things to do Place the spirit lamp at a central location visible to all learners.

Safety Precautions Tell the students to be careful while touching the materials or apparatus used in the experiment. Ask the learners who are performing the experiment to carefully follow all instructions.

SESSION Link to known information/previous activity We have learnt about combination reactions. Now let us learn about decomposition reactions.

Procedure Call 2 learners to the table, at random. Have them put on the mask and goggles. Ask one of them, learner 1, to note the colour of potassium permanganate by taking the one crystal and dropping in a beaker of water. Next, ask learner 2 to take a spatula of potassium permanganate in a dry boiling test tube. Ask learner 2 to hold the test tube securely with tongs. (Check if the test tube and tongs are secure.). Now ask learner 2 to hold the test tube over the spirit lamp, while making sure the test tube is turned away from the learner. Ask all learners to observe the changes. Ask learner 1 to introduce a lighted incense stick into the test tube (held with tongs by learner 2) and observe what happens. After the reaction is completed, as learner 1 to introduce a wet test tube brush into the test tube and slowly remove it, taking care to scrape the walls of the test tube. Ask all learners to observe the colour of the brush.

UNDERSTANDING THE ACTIVITY Leading questions 1) What is the colour of potassium permanganate crystals?

2) What happens when you heat the potassium permanganate crystals?

3) What happens to the lighted incense stick, when it is introduced into the test tube? Why does this happen?

4) What colour is observed when the test tube cleaning brush is removed from the test tube?

5) What are the products formed in the reaction?

6) What is this type of reaction called?

7) Why do we see dark purple fumes?

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8) What is the green residue that we see on the test tube brush?

9) Why does the lighted incense stick catch fire?

Discussion and Explanation 1. Potassium permanganate crystals are purple in colour 2. We observe dense purple fumes are coming out ofthe test tube, along with popping sounds 3. When the lighted incense stick is introduced, it catches fire inside the test tube because of chemical reaction 4. We see a green colour on the cleaning brush 5. Oxygen, manganese dioxide, potassium manganate i. 2KMnO4(s) ————→ K2MnO4(s) + MnO2 + O2 (g) 6. This type of reaction is a decomposition reaction becausein this reaction, a single compound splits or decomposes into two or more simpler substances. This reaction is of the type:

AB A + B It is just the opposite of a combination reaction 7. Manganese dioxide is released as gas. Its fumes are dark purple in colour 8. The residue is potassium manganate 9. Since oxygen gas is released during the reaction, the lighted incense stick catches fire

KEY MESSAGES 

A decomposition reactionis one in which a single compound splits into two or more simple substances under suitable conditions

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 15 min

ABL 4.4 LEARNING OBJECTIVE – What is a single displacement reaction?

Note to Instructor– This activity explains how single displacement reaction works.

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ADVANCE PREPARATION

Material List Material 1.

50 ml dilute hydrochloric acid

Number Required 1 per group

2.

4 granules of zinc

1 per group

3.

Test tubes

1 per group

4.

Dropper

1 per group

5.

Test tube stands

1 per group

6.

Matchbox

1 per group

7.

1 pair safety gloves

1 per group

8.

1 pair of safety goggles

1 per group

Things to do Prepare a dilute solution of hydrochloric acid.

Safety Precautions Tell the learners to be careful while touching the materials or apparatus used in the experiment and to carefully follow all instructions. Ask them to use gloves and safety goggles while performing the experiments.

SESSION Link to known information/previous activity We have learnt about combination and decomposition reactions. Now let us learn about single displacement reactions.

Procedure Divide the learners into 5 groups and distribute the material. Identify two learners in each group who will perform the experiment and instruct the others in the group to keep a safe distance. Ask one of the learners who is performing the experiment to take 4 granules of zinc in the test tube (learner 1 and learner 2). Ask all learners to observe the colour of the zinc granules. Ask learner 1 to pour a few drops of dilute hydrochloric acid into a test tube using a dropper. Ask learner 1 to pour the hydrochloric acid slowly into the test tube by adding it along the sides of the test tube. Ask all learners to observer the reaction. Now once bubbling is seen in the test tube, ask learner 2 to light a matchstick and slowly bring it near the mouth of the test tube. Once again, ask the learners to observe the changes.

Leading questions 1. What is the colour of zinc granules?

2. What happens when hydrochloric acid is poured into the test tube?

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3. What is the colour of zinc granules after the reaction?

4. What are the reactants and products in this reaction?

5. What happens when the lighted matchstick is brought to the mouth of the test tube? Why does this happen?

6. What is this type of reaction called?

7. Which element is displaced in this reaction and why?

Discussion and Explanation 1.

2.

3.

4.

Zinc granules are grey in colour We observe bubbling in the test tube The zinc granules turn black in colour The reactants are zinc and hydrochloric acid, products are hydrogen gas and black residue of zinc chloride.

Zn + 2 HCl  ZnCl2 + H2 (g)

5. The flame was put off with a “pop” sound. It is because of the gas that is evolved in the reaction 6. This type of reaction is a single displacement reaction because in this reaction, a more reactive element displaces the less reactive one from the compound. This reaction is of the type: A + BC  AC +B 7. In this reaction zinc is more reactive than hydrogen. It displaces hydrogen and bonds with chlorine to form zinc chloride. Hydrogen is emitted as gas. This is confirmed when the lighted matchstick goes out with a “pop” sound

KEY MESSAGES 

A Single Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 10 min

ABL 4.5 LEARNING OBJECTIVE – What is a double displacement reaction?

Note to Instructor– This activity explains how double displacement reaction works.

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ADVANCE PREPARATION Material List Material 1. Test tube with lead nitrate solution

Number Required 1 per class

2. Test tube with potassium iodide solution

1 per class

3. Empty test tubes

1 per class

4. 3 pairs of safety gloves

1 per class

5. 3 pairs of safety goggles

1 per class

Things to do Prepare and label test tubes of dilute lead nitrate solution and dilute potassium iodide solution. To prepare each solution, take a pinch of the respective salt in a test tube and add water to fill the tube. Make sure you label the solutions correctly. Prepare an area for the experiment at the front of the class which is visible to all learners.

Safety Precautions Tell the learners to be careful while touching the materials or apparatus used in the experiment and to carefully follow all instructions. Ask them to use gloves and safety goggles while performing the experiments.

SESSION Link to known information/previous activity We have learnt about single displacement reactions. Now let us learn about double displacement reactions.

Procedure Call 3 learners to the experiment area. Give the test tube with lead nitrate to learner 1, potassium iodide solution to learner 2 and the empty test tube to learner 3. Ask learner 1 and learner 2 to pour half of each solution into the empty test tube. Ask all learners to observe and compare the 3 test tubes.

Leading questions 1. What is the colour of each solution?

2. What happens both the solutions are poured into the empty test tube?

3. What are the reactants and products in this reaction?

4. What is the colour of the precipitate formed? What is the compound that precipitates?

5. Why do we not see lead nitrate in the test tube?

6. Which elements are displaced in this reaction and why?

7. What is this type of reaction called?

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2. A yellow coloured substance is formed which settles to the bottom of the test tube 3. The reactants are lead nitrate and potassium iodide. The products are lead iodide and potassium nitrate 4. The precipitate is yellow coloured compound - Lead iodide 5. Potassium nitrate is white in colour and cannot be seen because of the yellow colour of the lead iodide 6. Lead displaces potassium to form Lead iodide; Potassium displaces lead to form potassium nitrate.

Potassium is more reactive than lead, hence displaces Pb from Pb(NO3)2 Pb (NO3)2(aq) + 2KI

PbI2 + 2KNO3

7. This type of reaction is a double displacement reaction because in this reaction, an element from each of the reactants displaces the other to form new compounds. This reaction is of the type: AB + CD ďƒ

AD + CB

KEY MESSAGES 

A double displacement reactionis a chemical reaction in which an element from each of the reactants displaces the other to form new compounds

LEARNING CHECK Match the following: Nature of reaction

Reaction

1. Combination

a. 2 NaClO3 --> 2 NaCl + 3 O2

2. Decomposition

b. 4 Cr + 3 O2 --> 2 Cr2O3

3. Single Displacement

c. 2 K + 2 H2O --> 2 KOH + H2

4. Double Displacement

d. P4 + 5 O2 --> 2 P2O5 e. 3 AgNO3 + K3PO4 --> Ag3PO4 + 3 KNO3

(Ans: 1b, d; 2a; 3c; 4e)

WEB RESOURCES http://chemistry.about.com/od/chemicalreactions/a/reactiontypes.htm

ADDITIONAL INFORMATION FOR INSTRUCTOR Examples of Combination Reactions for Instructor understanding: Agastya International Foundation. For Internal Circulation only.

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Types of Combination reactions: Reaction between two or more elements: An example of this type of combination reaction is the reaction between a metal and a non- metal. Most metals react with non-metals to form ionic compounds. A good example of this would be:

2Na(s) + Cl2(g) ďƒ 2NaCl(s) Similarly, non-metals may react with highly active metals to form covalent compounds. Example, sulphur reacts with oxygen gas to form gaseous sulphur dioxide.

Reaction between elements and compounds: An element and a compound react to form another compound. Example, carbon monoxide reacts with oxygen gas to form carbon dioxide.

Reaction between two compounds: Two compounds react with each other to form a new compound.

Example, calcium oxide (quick lime) reacts with carbon dioxide gas to form calcium carbonate (lime stone).

Some examples of combination reactions for Instructor’s reference Combustion Reactions: Combustion of coal and combustion of hydrogen are examples of combination reactions.

Coal burns in air to form carbon dioxide gas.

Hydrogen burns in the presence of oxygen to form water in the form of steam. Upon cooling, it becomes liquid.

Formation of Ammonium chloride: Ammonium chloride is formed by combining vapours of ammonia with hydrogen chloride gas. It is a white-coloured solid.

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Formation of Sulphuric acid: Formation of sulphuric acid from sulphur trioxide is also a combination reaction. Sulphur trioxide on hydration forms sulphuric acid. This reaction is highly exothermic in nature.

Formation of ferrous sulphide: It is formed by heating fine pieces of iron with sulphur powder.

Manufacture of Ammonia: The manufacture of ammonia gas from nitrogen and oxygen is also a combination reaction.

Combination of sodium oxide and water: Sodium oxide combines with water to form sodium hydroxide.

Examples of Decomposition Reactions for Instructor understanding: Types of Decomposition Reactions: Decomposition reactions can be classified into three types.

Thermal decomposition reaction Electrolytic decomposition reaction Photo decomposition reaction Thermal decomposition reaction (Thermolysis) Thermal decomposition is a chemical reaction where a single substance breaks into two or more simple substances when heated. The reaction is usually endothermic because heat is required to break the bonds present in the substance.

Examples:

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Decomposition of calcium carbonate: Calcium carbonate (lime stone) decomposes into calcium oxide (quick lime) and carbon dioxide when heated. Quick lime is the major constituent of cement.

Decomposition of potassium chlorate: When heated strongly, potassium chlorate decomposes into potassium chloride and oxygen. This reaction is used for the preparation of oxygen.

If the decomposition is carried out in the presence of manganese dioxide (MnO2), it takes place at a lower temperature. In this case, MnO2 is used as a catalyst.

Decomposition of ferric hydroxide: Ferric hydroxide undergoes decomposition in the presence of heat, giving ferric oxide and water molecules.

Decomposition of hydrated oxalic acid: Hydrated oxalic acid (H2C2O4.2H2O) decomposes into oxalic acid and water when heated.

Electrolytic decomposition reaction (Electrolysis) Electrolytic decomposition may result when electric current is passed aqueous solution of a compound. A good example is the electrolysis

through an of water.

Electrolysis of water: Electrolysis of water is the decomposition of hydrogen and oxygen due to the passage of electric current through

water into it.

Decomposition of sodium chloride: On passing electricity through sodium chloride, it decomposes into sodium and chlorine.

molten

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Photo decomposition reaction (Photolysis) Photo decomposition is a chemical reaction in which a substance is broken down into simple substances by exposure to light (photons).

Decomposition of silver chloride: Place a small quantity of silver chloride (AgCl) taken in a watch glass under sunlight for some The crystals slowly acquire a grey colour. On analysis, it is found the sunlight has caused decomposition of silver chloride into silver and chlorine.

time. that

Silver bromide also decomposes in the same way.

Decomposition of hydrogen peroxide: In the presence of light, hydrogen peroxide decomposes into water and oxygen

Decomposition reactions are mostly endothermic Most decomposition reactions require energy either in the form of heat, light or electricity. Absorption of energy causes the breaking of the bonds present in the reacting substance which decomposes to give the product.

Examples of Single Displacement Reactions for Instructor understanding: How is the chemical reactivity of metals linked with their position in the electrochemical series?

Chemical reactivity of metals is linked with their relative positions in the activity series. Certain metals have the capacity to displace some metals from the aqueous solutions of their salts. A metal placed higher in the activity series can displace the metal that occupies a lower position from the aqueous solution of its salt.

The displacement reaction is not limited to metals only. Even nonmetals can take part in these reactions.

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Examples are halogens. The activity series of halogen is F > Cl > Br > I. An important thing to remember with single displacement reaction is that elements that form cations can only displace cations and elements that form anions can only displace anions.

Classification of single displacement reaction: I. II.

Cation replacement reaction Anion replacement reaction

Cation replacement reactions In this reaction, one cation replaces another one from its solution. A cation is a positively charged ion or metal. All metal displacement reactions are cation replacement reactions. Let us discuss some examples of cation replacement reactions.

Let us discuss some examples of cation replacement reactions.

1. If a strip of magnesium metal is placed in copper sulphate solution, the blue colour of copper sulphate disappears and the magnesium metal turns brown as the displaced copper is deposited on it. In the reactivity series, the position of magnesium is above that of copper. So it is more reactive than copper and it would displace copper from copper sulphate solution.

2. Also metals like Zn, Al, Pb, Fe, etc., displace Cu from copper salt solution. The chemical reaction can be written as:

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3. Iron displaces lead from the aqueous solution of lead nitrate.

4. If a less reactive metal is added to a salt solution of more reactive metal, nothing will happen.

5. Similarly, metals above hydrogen in the reactivity series displace hydrogen from dilute acids.

For example, a. The metals such as potassium, sodium, lithium, etc. react more vigorously with dilute acids forming metal salts and hydrogen gases.

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b. Metals such as aluminium, zinc, magnesium, iron, etc., react safely with dilute acids.

The reaction Zn with dil. H2SO4 is often used in the laboratory for the preparation of hydrogen gas.

Anion replacement reactions In this reaction, one anion replaces another one from its solution. An anion is a negatively charged ion or non-metal. For example, more reactive halogen replaces less reactive halogen from its solution.

1.

Chlorine displaces bromine from an aqueous solution of sodium bromide.

2.

Bromine displaces iodine from potassium iodide solution.

Examples of Double Displacement Reactions for Instructor understanding: Double displacement reactions can be further classified as neutralization, precipitation and gas formation reactions.

Neutralization Reactions Neutralization reactions are a specific kind of double displacement reaction. An acid-base reaction occurs, when an acid reacts with equal quantity of base. The acid base reaction results in the formation of salt (neutral in nature) and water.

On mixing an aqueous solution of hydrochloric acid with an aqueous solution of sodium hydroxide, sodium chloride and water are formed.

Precipitation Reactions Precipitation is the formation of a solid in a solution or inside another solid during a chemical reaction. This process usually takes place when the concentration of dissolved ions in the solution exceeds the solubility product.

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On mixing aqueous solutions of silver nitrate and sodium chloride, a white curdy precipitate of silver chloride is formed.

On mixing an aqueous solution of barium chloride with that of copper sulphate, a white precipitate of barium sulphate is formed.

On mixing an aqueous solution of lead nitrate with sodium sulphate, a white precipitate of lead sulphate is formed.

On passing hydrogen sulphide gas through copper sulphate solution, a black precipitate of copper sulphide is formed.

On adding a solution of lead nitrate to sodium iodide solution, a yellow precipitate of lead iodide is formed.

Cobalt(II) chloride reacts with sodium carbonate to form pink/red coloured precipitate of cobalt(II) carbonate and sodium chloride.

On adding aluminium sulphate solution to calcium chloride solution, a precipitate of calcium sulphate is formed.

Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.

Gas Formation Reactions

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A double displacement reaction should also occur if an insoluble gas is formed. Gases such as HCl and NH3 are soluble in water, but some other gases, such as H2S, are not soluble in water.

Many sulfide salts will react with acids to form gaseous hydrogen sulphide.

Insoluble gases are often formed by the breakdown of unstable double displacement reaction products.

For example, marble chips (CaCO3) react with dilute hydrochloric acid to form calcium chloride and carbonic acid. Carbonic acid is unstable and readily decomposes to form carbon dioxide and water.

ABL 5– Endothermic and Exothermic Reactions Activity

Learning objective

Key messages

Time (min)

5.1

What are exothermic reactions?



Chemical reactions that release energy in the form of heat, light or sound are called exothermic reactions

15

5.2

What are endothermic reactions?



Chemical reactions that need heat energy to proceed and absorb heat from the surroundings are called endothermic reactions

15

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Time: 15 min

ABL 5.1 LEARNING OBJECTIVE – What are exothermic reactions?

ADVANCE PREPARATION Material List Material 1. ½ tsp calcium chloride

Number Required 1 per group

2. 10 ml water in a clean plastic cup

1 per group

3. Thermometer

1 per group

4. 1 measuring cup

1 per class

5. Observation sheet 4

1 per learner

Chemical Reactions Observation Sheet 4.docx

Things to do Measure out the water and calcium chloride. Print out the observation sheets. (There are 2 tables per observation sheet. So, print out only half as many as needed.)

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Safety Precautions Instruct the learners to be careful while performing the experiment.

SESSION Link to known information/previous activity We have seen that some reactions give out energy in the form of heat, light, or sound. Let us learn more about such reactions.

Procedure Divide the class into 5 groups. Identify 2 learners in each group who will perform the experiment.

Instruct the other learners to observe while keeping a safe distance. Ask learner 1 place the thermometer in the cup of water. Learner 2 will read out the temperature of the water. Now ask learner 1 to carefully add the ½ tsp of calcium chloride to the water and place the thermometer in the plastic cup as the reaction is taking place. Learner 2 will observe the temperature and read out the highest temperature. Ask all the learners to record the temperatures in their observation sheets.

UNDERSTANDING THE ACTIVITY Leading questions 1.

2.

3.

4.

5.

What was the temperature of the contents of the cup before the reaction?

What was the temperature of the contents of the cup just after the reaction?

Was there any difference in the temperature?

What could be the reason for the increase in temperature?

Why is energy released in this reaction?

Discussion and Explanation 1.

2.

3.

4.

5.

Temperature of the cup before reaction is __________ Temperature of the cup after reaction is __________ Temperature increased after the reaction by ___________ Reaction might have released heat, which increased the temperature Calcium chloride and water react to form calcium oxide and hydrochloric acid and release heat energy in the process CaCl2 + H2O  CaO + 2HCl + energy

Energy is required to break the bonds between elements in a compound. Energy is released when bonds are formed between elements. Less energy is required to break the bonds in the calcium chloride molecules than is released when the calcium oxide and hydrochloric acid are formed. This excess energy is released as heat and the reaction is exothermic

KEY MESSAGES 

Chemical reactions that release energy in the form of heat, light or sound are called exothermic reactions

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LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

TRY IT YOURSELF Place a thermometer in a clean dry glass bottle and close the lid. Allow about 5 minutes for the thermometer to record the temperature, then open the lid and read the thermometer. Record the temperature. Soak a steel scrubber in some vinegar for 5 minutes. This removes the protective coating from the steel scrubber and allows it to rust. Now squeeze out the vinegar from the steel scrubber and wrap the scrubber around the thermometer. Use a rubber band to hold it in place. Now place the scrubber and thermometer in the glass bottle and close the lid. After 5 minutes, read the temperature on the thermometer and compare it with the first reading. Is there a difference in temperature? Why do you think this is so?

(When the iron combines with oxygen, heat is released)

Time: 15 min

ABL 5.2 LEARNING OBJECTIVE – What is an endothermic reaction?

ADVANCE PREPARATION Material List Material 1. 32g barium hydroxide octahydrate

Number Required 1 per class

2. 17g ammonium chloride

1 per class

3. 125ml or 250ml conical flask

1 per class

4. Glass stirring rod

1 per class

5. Small piece of cardboard

1 per class

6. Squeeze bottle of water

1 per class

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7. Thermometer

1 per class

8. 1 pair of safety gloves

1 per class

9. 1 pair of safety goggles

1 per class

10.Observation sheet 5

1 per learner

Things to do Print out the observation sheet.

Safety Precautions  Be aware that the temperatures achieved in this experiment are well below the normal body temperature and the reaction flask should not be handled for prolonged periods of time  Inhalation of concentrated ammonia vapour can cause serious respiratory problems . Tell students to be careful during the experiment Soluble barium salts are poisonous if ingested. Upon contact with the skin, barium and ammonium salts may produce minor irritations or cause allergic reactions. If the flask is spilled or broken, its contents should be flushed down the drain with large amounts of water. Hands should be thoroughly washed after handling this material. If clothes come in contact with this substance, they should immediately be removed. Any region of skin exposed to this compound should immediately be washed with cold water and a light soap.  Due to the ammonia vapour given off, the endothermic demonstration should not be done in a room with poor ventilation  Always were safety goggles when working with these chemicals

SESSION Link to known information/previous activity We have learnt about exothermic reactions. Do all reactions give out energy? No, there are some reactions that need to absorb heat in order to proceed. Let us learn about those.

Procedure Place the experimental set-up where it is visible to all learners, in a well-ventilated room. Open windows if necessary. Call 2 learners to assist with the experiment. Ask them both to put on the safety goggles and gloves. Ask learner 1 to touch the surface of the reaction flask. Ask learner 1 to transfer the pre-weighed amounts of solid barium hydroxide octahydrate and ammonium nitrate into the flask one at a time. Ask learner 2 to stir the two substances together with the glass rod and observe. Within 30 seconds the odour of ammonia will become apparent. Now ask learner 1 to lightly touch the surface of the flask. Ask him/her how the flask feels. Now ask learner 2 to place a small amount of water on a piece of cardboard and hold it (the side with water) to the surface of the flask and observe. Ask learner 1 to place the thermometer inside the flask and measure the temperature.

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UNDERSTANDING THE ACTIVITY Leading questions 1. How did the surface of the water feel before the reaction?

2. How did the surface of the water feel after the reaction?

3. What happens to the cardboard piece when it is held against the surface of the flask? Why does this happen?

4. What are the products of the reaction?

5. What is the temperature of the flask after the reaction?

6. Why is the temperature of the flask so low after the reaction?

Discussion and Explanation 1. The flask was normal to touch 2. The flask feels cold after the reaction 3. The cardboard piece sticks to the surface of the flask because the cold temperature of the flask freezes the water on the cardboard to ice 4. The products of the reaction are barium chloride, ammonia and water. The equation of the reaction is Ba(OH)2• 8H2O (s) + 2 NH4Cl (s)

BaCl2• 2H2O (s) + 2 NH3 (aq) + 8 H2O (l)

5. The temperature after the reaction is _________ 6. The temperature decreased after the reaction because, the reaction absorbed the heat energy and made the surroundings (flask) cool. The reactions which absorbs heat energy from the surroundings and proceed are called as endothermic reactions

Solid barium hydroxide reacts with solid ammonium chloride to produce barium chloride, ammonia gas, and liquid water. This reaction gets down to -20°C or -30°C, which is more than cold enough to freeze water

KEY MESSAGES 

Chemical reactions that need heat energy to proceed and absorb heat from the surroundings are called endothermic reactions

LEARNING CHECK Note to Instructor –This evaluation can be conducted as an assessment for ABLs 1 to 5. It can be done in the form of a worksheet, group exercise or a quiz. Students should be able to complete this in about 10 minutes.

Tell learners that they will now get a chance to see how much they have learnt about chemical reactions in the class. Tell them that they will get 10 minutes to complete the worksheet that will be handed to them.

Give out one worksheet per student. At the end, you can discuss the solution with the students and give them an opportunity to correct any misunderstandings that they may have.

QUESTIONS: Agastya International Foundation. For Internal Circulation only.

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1. Classify the reaction as chemical and physical change: (Heating of wax, burning of wood, melting of ice, boiling water, dissolving sugar in water and heating sulphur.)

2. What is the evidence of chemical reactions?

3. Translate the following equations into statements a. Zn + CuSO4 ZnSO4 + Cu b. Zn + HCl

ZnCl2 + H2

4. Match the following symbols A) Gas B) Solid C) Yields D) 5. Balance the equations a. NaOH + H2SO4

1) 2) (g) 3) (s) 4) gas evolved

Na2SO4 + H2O

b. NaCl +AgNO3

AgCl + NaNO3

c. BaCl2+ H2SO4

BaSO4 + HCl

6. Match the following

7. a. b. c. d.

Nature of reaction Reaction Combination ZnCO3 ZnO + CO2 Decomposition MgO + H 2O Mg(OH)2 Displacement 2KI+ CI2 2KCl +I2 Double Displacement NH3 + 3Cl2 NCl3 + 3 HCL What type of chemical reaction absorbs energy and requires energy for the reaction to occur?

Endothermic Exothermic Synthesis Both a. and b.

8. a. b. c.

Exothermic reactions can release energy in the form of: Heat Light Sound

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d. All of the above 9. Which of the following are examples of endothermic processes? (Select all that apply) a. Photosynthesis

c.

b.

3

4

Melting of ice

d.

Burning wood

Boiling water

5 6

10. Which of the following are examples of exothermic processes? (Select all that apply) a. Setting of concrete

b.

Burning wood

8

7

c.

Respiration

d.

Freezing of water

3http://www.phschool.com/science/biology_place/biocoach/photosynth/overview.html 4http://commons.wikimedia.org/wiki/File:Burning_Wood.jpg 5http://en.wikipedia.org/wiki/Ice_cube 6http://en.wikipedia.org/wiki/Boiling 7http://www.kilsaran.ie/build/product/rapid-setting-concrete/ 8http://commons.wikimedia.org/wiki/File:Burning_Wood.jpg

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9

10

WEB RESOURCES http://www.chem.umn.edu/outreach/EndoExo.html http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Chemical_Bonding/General_Principles/Bond_Energie s

ABL 6– Reversible and Irreversible Reactions Activity

Learning objective

Key messages

Time (min)

6.1

Can chemical reactions proceed in



Chemical reactions that proceed in the forward

9http://www.oum.ox.ac.uk/thezone/animals/life/respire.htm

10http://www.coolantarctica.com/gallery/scenic/Seaice%20formation/Antarctica_sea_ice2.htm

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20

both directions?



6.2

Can all reactions be reversed?



  6.3

What are reversible and irreversible reactions in our daily life?



direction as well as in the reverse direction simultaneously are known as reversible reactions These reactions never go to completion, but continue in both directions in a state of chemical equilibrium

Some chemical reactions proceed to completion in one direction only and are known as irreversible reactions Reactants are completely converted into products in a certain interval of time Products do not form reactants again Reversible and irreversible reactions are part of our daily life – Refer list for examples

20

20

Time: 20 min

ABL 6.1 LEARNING OBJECTIVE – Can chemical reactions proceed in both directions?

Note to Instructor– This activity examines if products and reactants of a reaction can be reversed.

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ADVANCE PREPARATION Material List Material 1. 2 test tubes

Number Required 1 per group

2.

3g copper sulphate

1 per group

3.

Bending straw

1 per group

4.

250ml flask

1 per group

5.

Spirit lamp

1 per group

6.

1 set clamp and stand

1 per group

7.

One-holed rubber cork to fit the mouth of the test tube 8. Test tube stand

1 per group

9.

1 per group

Match box

1 per group

10. 1 pair safety gloves

1 per group

11. 1 set safety goggles

1 per group

Things to do Arrange the set up prior to experimentation by clamping the test tube to stand Safety Precautions Instruct the learners to be careful while performing the experiment. Make sure they wear safety gloves and goggles.

SESSION Link to known information/previous activity We have been learning about different kinds of reactions. Let us learn more about reactions that can be reversed and those that cannot.

Procedure Divide the class into 5 groups. Provide the experimental set up to the groups. Draw the experimental set up on the board. Help the learners to set up the experiment as shown in the figure. Ask the learners to note the colour of the copper sulphate powder. Ask 1 learner from each group to gently heat the test tube with copper sulphate for a few minutes. Ask all the learners to observe the change in colour of copper sulphate and the product formed in the test tube in the water bath. Ask the learners to identify which are the reactants and which are the products.

Help the learners to carefully remove the set up without disturbing the chemicals. Cool the powder for a few minutes and then add the product collected in the test tube to that powder.

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Figure 2 – Copper sulfate experimental setup

UNDERSTANDING THE ACTIVITY Leading questions 1.

2.

3.

4.

5.

6.

7.

8.

9.

What is the colour of the copper sulphate?

Why is one test tube placed in the beaker of cold water?

What happened when copper sulphate was heated?

What was collected in test tube kept in beaker of cold water? Why do you think that product was formed?

What happened when product collected in test tube was poured in the test tube having powder?

What are the reactants and what are the products?

Can these products be reversed to form reactants?

What are the characteristics of reversible reactions?

What are examples of reversible reactions in our daily life?

Discussion and Explanation 1.

2.

3.

4.

Copper sulphate is blue in colour The test tube is placed in the beaker of cold water to condense the product formed When copper sulphate is heated, it becomes a white powder Water collects in the test tube that was placed in the water bath. The original reactant might contain water in it.

5. Copper sulphate again turns blue in colour 6. The reactant is hydrated copper sulphate and the products are anhydrous copper sulphate and water 7. Most chemical reactions are irreversible, which means that the reaction moves in only one direction. But there are some reactions, which can proceed in directions, forwards and reverse, from reactants to formation of products and from products to formation of reactants. These kinds of reaction are called reversible reactions

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Here, copper sulphate is the reactant and it is blue in colour. When we heat this, it changes into anhydrous copper sulphate by losing water in the form of water vapour. The lost water, condensed in the test tube kept in the water. The products formed are anhydrous copper sulphate and water.

When these products are mixed, we get our original reactant, (hydrated) copper sulphate, which is blue in colour.

8. Reversible reactions are represented by double headed arrow, which indicates that the reaction takes place both ways (reactants to products and again from products to reactants) 9. Hydrated copper (II) sulphate + heat anhydrous copper (II) sulphate + water Reversible reactions can be started from either side. These reactions are never complete; they have a tendency to attain a state of chemical equilibrium where the rates of the forward and reverse reactions are equal We see examples of reversible reactions in our daily lives: 

Examples of reversible reactions are: o Neutralization between an acid and a base either of which or both are weak: CH3COOH + NaOH  CH3COONa + H2O o Evaporation of water in a closed vessel: H2O(l)  H2O(g) Examples of reversible reactions in our daily life are: o When we charge our cell phones every day, a reaction discharges energy from the cell phone battery. When we connect the batteries to a power point, the batteries are charged again. o In fact reversible chemical reactions happen in our blood every day. Haemoglobin is a molecule in our blood. When blood reaches our lungs, haemoglobin combines with oxygen to form oxyhaemoglobin. When the blood reaches the tissue, it releases oxygen and combines with carbon dioxide to form carboxyhaemoglobin. Again when it comes back to the lungs, it releases carbon dioxide, combines with oxygen and forms oxyhaemoglobin again.

KEY MESSAGES  

Chemical reactions that proceed in the forward direction as well as in the reverse direction simultaneously are known as reversible reactions These reactions never go to completion, but continue in both directions in a state of chemical equilibrium

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

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ABL 6.2

Time: 20 min

LEARNING OBJECTIVE – Can all reactions be reversed?

Note to Instructor– This activity examines if all reactions can be reversed.

ADVANCE PREPARATION Material List Material 1. 10g ammonium dichromate

Number Required 1 per class

2. 2 petri dish

1 per class

3. Wick dipped in ethanol

1 per class

4. 1 pair tongs

1 per class

5. Large glass tray

1 per class

6. Empty glass beaker

1 per class

7. Matchbox

1 per glass

8. 1 pair of safety gloves

1 per class

9. 1 pair of safety goggles

1 per class

Things to do Print out the observation sheet.

On a petri dish, make a conical heap of about 10 g of ammonium dichromate(VI) Place it on a metal tray to collect the large volume of chromium(III) oxide produced.Soak about a 3 cm length of a wooden spill in ethanol. Stick this into the top of the pile so that about 2 cm protrudes, to act as a wick.

Safety Precautions Ask learners to keep a safe distance from the experimental set up.

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SESSION Link to known information/previous activity We have learnt about reversible reactions. Let us see if all reactions can be reversed.

Procedure Place the experimental set-up where it is visible to all learners, in a well-ventilated room. Open windows if necessary. Light the wick. Wait for the reaction to complete (30 – 45seconds) Use tongs to hold a petri dish above the reaction allowing for steam to condense. Cover the petri dish with a beaker or another glass cover to prevent inhalation of un-burnt ammonium dichromate

UNDERSTANDING THE ACTIVITY Leading questions 1. What happens to the bright orange powder – the ammonium dichromate?

2. What are the reactants and the products?

3. Can you get back the bright orange powder from the green powder?

4. Why can’t the reaction be reversed?

5. What are the characteristics of irreversible reactions?

6. What are examples of irreversible reactions in our daily life?

Discussion and Explanation 1. As the wick burns down into the orange powder (ammonium dichromate), it burns like a volcano giving off smoke and decompose into a flaky green solid (chromium oxide) resembling dry tea leaves with a much larger volume than the original compound. Some of this oxide shoots into the air during the reaction.

2. The reactant is ammonium dichromate which produces chromium oxide, nitrogen gas and

water in the form of steam. The equation for this reaction is:

(NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + 4H2O(l) 3. It is not possible to get back the orange powder from the green powder 4. Not all the reactions can be reversed; only a few reactions are reversed. Majority of reactions proceed only in one direction. i.e. from reactants to formation of products. Once the product is formed the reaction stops. Such reactions which proceed in one direction are called are irreversible reactions 5. Irreversible reactions can proceed only in the forward direction. These reactions can proceed to completion 6. Examples of irreversible reactions are: o Neutralization between strong acid and strong base e.g., NaOH + HCl –> NaCl + H2O + 13.7 kcal o Double decomposition reactions or precipitation reactions e.g., BaCl2(aq) + H2SO4(aq) –> BaSO4(s) ↓ + 2HCl(aq)

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KEY MESSAGES   

Some chemical reactions proceed to completion in one direction only and are known as irreversible reactions Reactants are completely converted into products in a certain interval of time Products do not form reactants again

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 20 min

ABL 6.3 LEARNING OBJECTIVE – What are the reversible and irreversible reactions in our daily life?

Note to Instructor– This is a brainstorming activity. Accept all answers while the brainstorming is going on. Later, when the learners share their findings, you can point out any mistakes that may come up.

ADVANCE PREPARATION Material List Material 1. 2 sheets of un-ruled paper

Number Required 1 per group

2. Chart paper

1 per group

3. 5 sketch pens of different colours

1 per group

Things to do Not Applicable Safety Precautions Not Applicable

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SESSION Link to known information/previous activity We have learnt about reversible and irreversible reactions. Let us now see if we can think of any such reactions that we may have observed in our daily life.

Procedure Form 5 groups and distribute the material. Ask them to discuss and brainstorm to identify reversible and irreversible reactions that they may have observed in daily life. Explain the rules of brainstorming to them: All ideas are welcome; no negative comments on any ideas; each learner comes up with at least 2 ideas.

Ask the learners to discuss and write down these ideas on the paper and prepare the chart. Conduct a discussion where they will share these findings with the class.

UNDERSTANDING THE ACTIVITY Leading questions 1. What are the reversible reactions you see in your daily life?

2. What are the irreversible reactions you see in your daily life?

Discussion and Explanation 1. Examples of reversible reactions are phenomena where steam turns to water.

2. Examples of irreversible reactions are aging process in all living things.

LIST OF SOME REVERSIBLE AND IRREVERSIBLE REACTIONS THAT OCCUR IN DAILY LIFE – you could introduce some of these to the learners during the discussion REACTION EXAMPLE Reversible

Boiling water, freezing water etc When you breathe on the inside of a glass window when it is cold outside, a mist appears. This is nothing but condensed water vapor that evaporates after some time on its own. Thus it is a reversible process.

Irreversible

All cooking processes involving heating – baking bread, frying an egg etc change the properties of the material that we are cooking and we cannot get the raw materials again from the cooked food.

Irreversible

Burning a paper leads to formation of a new product ash and we cannot get paper back from the ash. All burning reactions are irreversible.

Reversible

Dissolving salt or sugar in water. When you mix salt or sugar in water, a solution is formed which is different from water and sugar, but when you heat up the solution so that water evaporates, you can get back sugar or salt thus proving that the reaction is reversible and you can get back the original products of the reaction.

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Reversible

Another example concerns light-sensing sunglasses. Copper oxide and silver halide are added to the lenses to produce a darkening reaction in the sunlight. When in the shade, the copper oxide and silver halide reverse their reactions to create clear lenses again.

Reversible

Respiration - Hemoglobin molecules can either bind to carbon dioxide or oxygen. As blood travels through the alveoli of the lungs, hemoglobin molecules pick up oxygen-rich molecules and bind to the oxygen. As the hemoglobin travels through the rest of the body, it drops off oxygen at the capillaries for the organ system to use oxygen. After expelling the oxygen, it picks up carbon dioxide.

Because this process is constantly carried out through the body, there are always hemoglobin molecules picking or expelling oxygen and other hemoglobin molecules that are picking up or expelling carbon dioxide. Therefore, the hemoglobin molecules, oxygen, and carbon dioxide are reactants while the hemoglobin molecules with oxygen or carbon dioxide bound to them are the products. In this closed system, some reactants convert into products as some products are changing into reactants, making it similar to a reversible reaction.

KEY MESSAGES 

Reversible and irreversible reactions are part of our daily life (refer list for examples)

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

WEB RESOURCES http://www.nuffieldfoundation.org/practical-chemistry/ammonium-dichromate-volcano

REFERENCES: 1) National Council of Educational Research and Training, Class X, November 2012.

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1.2 Activity Cards: What is a chemical Change?

Note to Instructor: Print out (try to get a colour print) these activity cards. Cut and separate them. One set for each group:

Frying Egg

Burning wood

Slicing Vegetables

Boiling water

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Melting Ice

1.2 Observation sheet 1: What is a chemical change?

Name: Class:

Activity

School:

Describe before change (colour, state, size etc)

What was happening during change?

Describe after change

Is it a temporary or a permanent change?

Why?

Melting of wax Heating of sulphur Dissolving of sugar Heating sugar Cutting of Mg strip Heating of Mg strip

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Is it a chemical or physical change?

Why?

2.2 Observation sheet 2: What are the indicators of a chemical reaction?

Name: Class:

School: Vinegar

Calcium chloride

Iodine

Lemon juice

+ Baking soda

+ Baking soda

+ Starch

+ Red cabbage juice

Observations

Heat Cold

Bubbling & Fizzing Solid formation at the bottom of test tube Colour change

Is this a chemical reaction?

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2.3

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3.1 Basic Symbols Flashcard: What are the basic symbols, coefficients and subscripts in a chemical equation?

Instructions for Instructor: Print out (try to get a colour print) of this sheet on a thick cardboard sheet if possible. Cut out the cards.

Set 1:

(l) Set 2:

(aq )

Precipitate formed in the reaction

Reactant or product in a liquid state

Reactant or product in a solid state

Aqueous solution "dissolved in water"

(g ) (S (+ ) )

“AND” Separates two products or two reactants

Gas evolved in the reaction

Reactant or product in a gaseous state

“YIELDS” Separates reactants from products

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3.1

3.1

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3.1

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3.1 Chemical Reactions – Coefficients and Subscripts Worksheet: What are basic symbols, coefficient and subscripts in chemical equations?

Name:   

Class:

School:

Circle each subscript in each chemical formula.

Draw a square around each coefficient.

Answer the questions related to each chemical formula based on previous knowledge

a. O2 What element does the O represents? ____________ b. CO2 How many atoms of each element are in the formula shown? __________ c. 5H2 How many atoms of each element are in the formula shown? __________ d. 2C2H6 How many atoms of each element are in the formula shown? __________ e. 2Na2SO4 How many atoms of each element are in the formula shown? __________ f. CaCl2 How many atoms of each element are in the formula shown? __________ Observe: Coefficient is a whole number not fractions. 

Label the chemical equation using PRODUCT, REACTANTS, SUBSCRIPT, COEFFICIENT, and YIELDS

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3.1 Observation sheet 3: What is the law of conservation of mass?

Name:

Class: Mass of the closed set-up before the reaction in grams

Name:

Class: Mass of the closed set-up before the reaction in grams

School: Mass of the closed set-up after the reaction in grams

Mass of the open set-up after the reaction in grams

School: Mass of the closed set-up after the reaction in grams

Mass of the open set-up after the reaction in grams

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3.3 Balancing Equations Worksheet: What is a balanced equation?

Name:

Class:

Time: 10 Min

School:

Reaction 1:

Reaction 2:

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COMBINATION A+B

AB

DECOMPOSITION AB

2 H2O → 2 H2 + O2

A+B

SINGLE DISPLACEMENT A + BC

H2 + O2→ 2 H2O

Zn + 2 HCl → ZnCl2 + H2

AC + B

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Reactio n 3:

DOUBLE DISPLACEMENT AB + CD

NaCl+ AgNO3→ NaNO3 + AgCl

AD + CB

CHEMICAL REACTIONS

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TYP ES OF

5.1 Observation sheet 4: What is an exothermic reaction?

Name:

Class:

School: Temperature in 0C

Trial 1

Trial 2

Trial 3

Solutions Water Water + Calcium chloride Change in temperature

Name:

Class:

School: Temperature in 0C

Trial 1

Trial 2

Trial 3

Solutions Water Water + Calcium chloride Change in temperature

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