ACIDS, BASES AND THE PH VALUE: ASSESSMENT: Investigation, Observation and Evidence Based Questions The assessment is going to be an investigation , in which learners will get a chance to observe how the cabbage water solution react to change into different colors when added to various solutions of PH scales. The assessment covers two parts: i)
The first part is an interactive chart designed to let the learners That is where we are trying to test learner’s conceptual understanding of acids and bases. These is trying to cover that section of planned questions of a lesson. The planned questions. What measurement can we use to decide whether something is an acid or a base? What does ‘the PH the scale’ refer to? How can we measure the PH of a substance? What does it means if a substance has a PH below 7 (PH <7)? What does it mean if a substance has a PH above 7 (PH>7)? What does it mean when a substance has a PH equal to 7 (PH=7)? What is a universal indicator? How does a universal indicator respond to substances that are acidic, basic or neutral? Learners also make use of posters to identify acids and bases The second part of assessment is learner activity inquiry Learners are given instructions so that they learn to learn how to measure acidity and basicity Once again there are few terms to be defined by learners using their textbook. The terms are defined so that learners have clear understanding of how the PH scale is used to measure an acidity of substance Therefore learners are required to do the following: Define PH Identify PH scale
PH scale ranges between values of 1 and 14 The PH scale is visualized first using drawings and colors which can be used to describe where substances fall into the PH scale But because we are dealing with learners, it is compulsory that we have to give them an investigation, on which they have to gather evidence concerning how do we make use of PH scale to measure and visualize the acidity of a substance / substances.
This simple, means that we have to design a leaner activity onto which learners have to earn their active participation through making use of various instruments and material to investigate. Learnerâ&#x20AC;&#x2122;s task is to follow instruction given and manipulate learning resources that are used for their experiment. They also need to observe so that they record evidence to e used to answer questions concerning the a Method: Learners acquire a colorful labelled chart from a teacher so that they observe how the acidic and basic substances are spread on the PH scale. In chemistry, PH is a scale used to specify how acidic or basic a substance is. Water is neither basic nor acidic, therefore it has a PH scale of zero (0). This is called neutral level of PH scale. PH has universal indicators that is made of several compounds that several smooth colors which are then used to rate how different solutions may exhibit their PH value to the PH scale, and that is useful as we shall use it to determine if the solution is acidic or basic. It indicates acidity or alkalinity of the solution. Learners need to observe the following table to be used for observation when carrying this experiment. PH Range <3 3-6 7 8-11 >11
Description Strong Acid Weak Acid Neutral Weak Alkali Strong Alkali
Colour Red Orange or Yellow Green Blue Violent or Indigo
A: The chart below shows: PH scale?
D) Around 9-14, on the PH scale the level of a alkalinity Increases?
Increasing Alkalinity
E) Example of acid may include, 1 Bleach, 2Soapy water, 3 Ammonia solution.
C: Around 7 PH scale is Neutral
Neutral e.g.: water
B) PH scale range from 1-
14
C) From 5- 1 Acidity level increases
Increasing Acidity
Universal Indicator can show us more about how acidic or basic solution is. On the previous table of PH scale there are different colors that are spread around the statistics. Those different colors are the ones that indicate whether substance is acidic, natural, and or basic. When these different colors are aligned to the PH scale they bring about what we call Universal Indicator. The Universal Indicator can have many different colors, from red for strong acids to dark purple for strong bases. In the diagram below, the liquid inside the middle, test tube is neutral (PH = 7), and this is shown by green color of indicator. (Megan, 2017) It is wise to get a colourful printout so that learners observe colours of universal indicator.
Today, things like Litmus, are also used as Universal Indicators which comes in paper form so that. How do you think Litmus Universal Indicator can be used?
The Litmus Universal Indicator paper has PH colors that match arrangement of colors on the actual PH scale. As such, the Litmus Universal Indicator range from 1- 14 and each color matches exactly what is supposed to appear on the PH scale. This learner activity is going to investigate whether Universal Indicator and cabbage can be sued to show whether one substance is more acidic or basic than another. (Megan, 2017) Questions: Give an investigation question of this investigation. 1) What question are we trying to answer with this investigation?
Hypothesis: 2) What do you think the answer to the investigative question is? You should try to make a prediction. Identify Variables 3) What will you be changing in this investigation? What is this variable called? Material: i)The Universal Indicator is red cabbage , ii) Knife or blade , iii) 14 small glass beakers , plate or tray for onto which red cabbage is going to be cut. Get another bigger glass beaker onto which a crushed cabbage will inserted. Water cattle for boiling water. Why do we use red cabbage?
Red cabbage, as many other vegetables contains natural diets like anthocyanin, which gives fruits and leaves their different colours. The colour of these substances will depend on the acidity of their environment. For example, the colour of ripe fruit often change from green to red and from yellow to red. Once the cabbage is settled in water for approximately 20 minutes, the results in the liquid is shown â&#x20AC;Ś.with few tabs, by pouring cabbage solution into different small beakers with different mixtures of solution to react with cabbage solution.
Precaution: Learners must not Experiment instructions: a) Cut one quarter of a cabbage and lace it on the container, the larger beaker. b) Paw boiling water into a beaker with a red cabbage pieces , crushed into small pieces c) Leave boiled water to the large beaker with cabbage for 20 minutes d) Use a funnel / cone shaped flask with a paper to infiltrate cabbage water from the leaves of a cabbage. e) Now ‘dispose off’ the cabbage leave material remains in a large beaker and wash a container f) Paw water into an empty large beaker and leave a space for cabbage water solution to be mixed together. g) Paw cabbage water solution from coned flask into a larger beaker with ‘water solution’ and allow dilution process to take place. This is to ensure that solution is not is sour saturated. h) After having taken water from the cone shaped flask and paw it into larger beaker with a pure water, the water becomes universal indicator. i) How? j) The indicator is going to be poured into seven different beakers, with diverse reactants which shall emit colours that are interpretable using PH scale colours called universal indicators. Learners need to observe and compare and interpret whether substance is acidic or basic solution. k) Prepare seven different beakers , place beakers in series
Pour your universal indicator to each and every beaker, before you add other reactant as instructions are given below. l)
1st Beaker
2nd Beaker
3rd Beaker
4th Beaker
5th Beaker
6th Beaker
7th Beaker
Pour in Sulphuri c Acid (
Pour in Acidic Acid
Pour in Spark Water It has soda with carboni c acid
Add nothing
Baking soda solutio n
Ammoni a
Pour in strong base called sodium hydroxide
Colour Change : Observation by learners : interpretation by comparing both the solutions and universal indicators Where possible learners use the additional worksheets to determine colour of solution but that should be linked to what they are observing 1st = red
2nd=black pink
3rd=light pink
4th=original colour
5th = Blue
6th= Green
7th= yellow
PH scale : Strong Acidic Increasing Acids
0
Neutral
Alkalis Increasing Alkalis
Use an arrow to indicate direction of increasing of acidic and basic solutions on the space below Neutral Assign PH scale Number : in a space below 7 14
Account for reasons of why there are changes to the colour of solution of each beaker. Use PH scale record to support reason for your answer to what you may have observed to reaction of each solution of different beakers. Hint: cabbage water solution was used as a universal indicator, and Learners may make use of their textbooks and internet sources to answer this question. However the responses need to correspond to the aim of this investigation and relevant material used when conducting this experiment. 1st =
2nd
3rd
4th
5th
6th
7th
Answer: Small beakers have *different chemical substances added to each beaker to change colours
Make use of the table above to fill in the empty spaces:
Colour Change Beaker 1st Beaker
Red
2nd Beaker 3rd Beaker
Black Pink Light pink
4th Beaker 5th Beaker
Original / Blue
6th Beaker 7th Beaker
Green Turn green at first / light green
Chemical Formula
Reasons of Colour Change
It contains carbonic acid
PH scale
Reactant added
1
Sulphuric Acid Acidic Acid Sparkling water ( has soda )
4
8-9 12/13 14
Baking Soda Ammonia Sodium Hydroxide (strong base)
Define the term reactant
Memorandum:
Questions based on learner activity - investigation What happen to plant when acidity changes on the environment? Plant may change colours as well. Why was red cabbage used for this experiment? Answer: Red cabbage contains natural diets like anthocyanin like many other vegetables. The colour of these substances depends on the acidity of their environment. This diet constituent can be â&#x20AC;&#x2DC;derivedâ&#x20AC;&#x2122; using hot water, then which appear as cabbage water solution. This cabbage water can be prepared to become universal indicator when different chemical substances are added experimentally. (Megan, 2017) Name few physical items that falls under acid substances Answer: Name few basic substances Answer: Why was solution diluted to water? Answer: To enable solution not to be sour saturated Was your hypothesis matching the outcome of this investigation, explain? The answer is learner dependent.
Why water was added to universal indicator solution of cabbage water residue? Adding water to an acid or base will change its PH. Water is mostly water molecules so adding water to an acid or base reduces the concentration of ions in the solution. What conclusion can you draw from the experiment above? Universal indicator has different colours at different at different PH values. The colour chart can be used together with universal indicator to determine if substance is acidic or basic. The colour chart correspond to ranges of colours of universal indicators and the PH values are used to interpret whether substance is acidic or basic. Universal indicator has different colours at different PH values ranging from 1-14. Neutral solution take PH value of 7. Strong basic solution has a value of 0-6 and the concentration of acid substance increase as you move towards from 6 to 0. Similarly, Basic solution increase as you move from 8-14, and the concentration of alkalinity increase as you move from 8-14 with PH scale value. The universal indicators are used to exhibit / showcase different colour ranges of reactions on a PH scale. Red cabbage water solution can be used as universal indicator because it has ability to change different colours when diverse chemical reactants (chemical substances) are added to it as a universal indicator. (Megan, 2017) Draw a table to tabulate difference between acids and bases
Challenges â&#x20AC;&#x201C; Questions What is the reaction between an acid and a base called? Acid-base reaction What happens to the pH when an acid and a base are mixed? The substance solution becomes neutral Does the reaction between an acid and a base always give a neutral mixture, in other words a mixture with pH = 7? No it depends on level of concentration of reactants Which factors will determine the pH of the final solution when an acid and a base are mixed? Universal indicator paper such as litmus paper Is there a way to predict which classes of compounds will tend to be acids and which will tend to be bases?
Universal indicator paper such as litmus paper Reactant is a substance that takes part in and undergoes change during a reaction. What were acid reactant during this investigation? What were dependent and independent factors during this investigation?
Power Point:
Summary: When we want to decide whether a solution (in water) is acidic or basic, we can measure its pH. One of the ways pH can be measured, is with an acid-base indicator, such as universal indicator. An acid-base indicator is a substance that changes its colour depending on the pH of the solution that it is added to. The pH scale ranges between 1 and 14: - Acids have pH values lower than 7; - Bases have pH values higher than 7; and - Neutral substances have pH values approximately equal to 7. How acidic or basic a solution is, depends on its relative pH value: -The more acidic a solution is, the closer its pH value will be to 0; and -The more basic a solution is, the closer its pH value will be to 14. Concept Map: What can you use to determine whether a substance is an acid, base or neutral? Fill this in on the concept map. Finally, complete it by completing the information for the universal indicator. Fill in acid, base or neutral, depending on the colours listed.
References:
Megan, B (2017) ‘Natural Science Grade 09: CAPS – Explore World Without Boundaries’, Siyavula Technology Powered Learning (editors), pp (004-278).