Making Useful Materials
Grade
Title
Teacher
Student
G10 Chemistry: Making Useful Materials Calendar
Week
Date
Activity
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G10 Chemistry: Making Useful Materials AB Assessment – Chemical Industry
The chemical industry converts raw materials, such as crude oil, natural gas, minerals, air and water, into useful products. The products include chemicals to use as dyes, food additives, fertilisers, paints and pharmaceutical drugs. The industry makes bulk chemicals on the scale of thousands or even millions of tonnes per year. Examples are ammonia, sulphuric acid, sodium, hydroxide, chlorine and ethane. On a much smaller scale, the industry makes fine chemicals such as drugs and pesticides. It also makes small quantities of speciality chemicals needed by other manufacturers for particular purposes. These include such things as flame retardants, food additives and the liquid crystals for computer displays. The pie chart on the next page shows the range of products made by the chemical industry in the U.K. Your task is to; •
Select one of the categories shown in the chart.
•
Identify one use of the chemicals in your chosen category – one situation in which your category of chemicals can solve a particular problem or issue.
•
Discuss the problem or issue.
•
Discuss how your choice of chemical can solve or help to address the problem or issue.
•
Discuss and evaluate the implications of using your choice of chemical in solving the problem.
Your assessment should. •
Use a mixture of text and graphical sources
•
Contain no more than 1200 words
•
Be fully referenced using the MLA format and contain a bibliography.
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Pharmaceuticals, 31.5
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Other specialities, 13.0
Synthetic fibres, 2.0
Plastics and synthetic rubber, 7.5
Fertilisers, 1.0
Basic organics, 12.0
Basic inorganics, 2.5
Dyes and pigments, 3.0
Agrochemicals, 3.0
Industrial Glass, 5.0
The Chemical Industry
Paints, varnishes and inks, 8.0
Soaps, toiletries and cleaning preparations, 11.5
G10 Chemistry: Making Useful Materials
G10 Chemistry: Making Useful Materials DEF Assessment - Electrolyte
D, E, F Investigate, quantitatively, one aspect affecting electrolysis of solutions. You will be provided with the following 1M solutions: •
Hydrochloric acid- HCl
•
Sodium chloride- NaCl
•
Calcium chloride -CaCl2
•
Aluminium chloride- AlCl3
•
Copper sulphate – CuSO4
You have access to the usual electrolysis apparatus including copper metal and carbon electrodes.
You should; •
Design an experiment to investigate the rate of electrolysis of one of these solutions quantitatively.
•
Collect repeated and reliable data.
•
Process your data appropriately
•
Present your processed data in the form of charts as appropriate.
•
Analyse your data to establish any trends or patterns.
•
Evaluate the reliability of your plan and validity of your conclusions.
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G10 Chemistry: Making Useful Materials Oxidation and Reduction
Ion formation review (half-equations) Positive ions
Negative ions
Formation
Examples/ halfequations
Sample Problem 1: Express with half-equations the formation of these ions from their corresponding atoms: a) Positive ions; Na+, Mg2+, Al3+
b) Negative ions; S2-, N3-, Cl-
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G10 Chemistry - Making Useful Materials Jun2013
to fill in the columns of this table
2H2 + O2 2H2O
Use the equation:
Examples
electron transfer
oxygen gain/loss
Definitions
7
Li – 1e- Li+
Oxidation
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O2 + 2x2e- 2O2-
Reduction
Oxygen molecule
Oxidizing Agent
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Oxidation and Reduction
G10 Chemistry: Making Useful Materials
Li Atom
Reducing Agent
Oxidation Is Loss, Reduction Is Gain
SO2
CO
CO2
O2
O2
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+
+
NO2
Mg
+
+
+
Fe2O3
Fe
CH4
+
MgO
8
NO
Fe
Fe2O3
CO2
+
+
+
H2O
C
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SO3
CO2
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Sample Problem 2: Balance each of the reactions below and identify the oxidation and reduction that is occurring based on the oxygen gain/loss definitions:
OIL RIG
Gaining Electrons is Reduction
LEO says GER: Loosing Electrons is Oxidation,
Memorization ideas:
Oxidation and Reduction
G10 Chemistry: Making Useful Materials
Cl2
K +
Ca3N2
KCl
Na2O
Al2O3
MgO
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N2
O2
Na +
Ca +
O2
O2
Al +
Mg +
Equation
9
Oxidation
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Reduction
Sample Problem 3: balance the equation and then complete the table.
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Oxidizing Agent
Oxidation and Reduction
G10 Chemistry: Making Useful Materials
Reducing Agent
Total Number of Electrons Transferred
G10 Chemistry: Making Useful Materials Redox
1) Balance the following equations and identify the oxidizing and reducing agents. H 2
+
O2
H2O
Mg
+
O2
MgO
N
+
H2
NH3
+
Cl2
NaCl
Al2O3
2
Na Al
+
CuO
Mg
+
FeCl3
+
MgCl2
Cu +
Fe
2) Turn these word equations into symbol equations and identify the oxidized and reduced substances.
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G10 Chemistry: Making Useful Materials Investigating Redox Reactions
Redox reactions are often accompanied by colour changes. In this laboratory activity you will observe some of them and apply your knowledge of oxidation-reduction definitions.
Materials and safety equipment: Get the following equipment before you start the experiment: •
Put on safety goggles and lab apron;
•
2-3 test-tubes;
•
Test-tube rack
•
Droppers;
•
50 or 100 ml beaker;
•
Well-plate.
Experiment 1: Measure 5 mL of 0.5M FeSO4 solution using a measuring cylinder. Transfer the solution into a test tube. Add 7 drops of 2M H2SO4. Now add one drop of this solution to a beaker in which you put 2.5 mL of KMnO4 solution. Note the colour change. Add another drop. Continue to add drops of the FeSO4 solution until the colour does not change. Discard the solution from the beaker in the sink. The equation for the reaction is:
8
5! "
"
4 "
5! $
Observations and Conclusions. In your conclusion identify the oxidizing agent, the reducing agent, the substance that is oxidized and the substance that is reduced.
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G10 Chemistry: Making Useful Materials Investigating Redox Reactions
Experiment 2 Measure 5.0 ml of 0.01M K2Cr2O7 solution a clean beaker. Add drop by drop of FeSO4/H2SO4 solution from experiment 1 and record your observations. The equation for the reaction is:
" %"
14 3 ! "
2 $
7 "
3 ! $
Observations and Conclusions. In your conclusion identify the oxidizing agent, the reducing agent, the substance that is oxidized and the substance that is reduced.
Experiment 3 Measure 10 ml of 10%H2O2 solution a clean beaker. Add drop by drop of KI solution and record your observations. The equation for the reaction is:
2 " " 2* *" " 2 "
Observations and Conclusions. In your conclusion identify the oxidizing agent, the reducing agent, the substance that is oxidized and the substance that is reduced.
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G10 Chemistry: Making Useful Materials Investigating Redox Reactions
Further experiments Use small amounts of solutions (5 to 10 ml) to try the following redox reactions. Try to balance the equations and determine which is the oxidizing and which is the reducing agent. a) A solution of potassium iodide is mixed with an acidified potassium dichromate solution. To balance the reduction of the Cr6+in the dichromate ion to Cr3+, the iodide ion must be undergo oxidation.
" %" 14 2 *
2 $
*"
7 "
b) A solution of potassium permanganate is added to an acidified solution of hydrogen peroxide. To balance the reduction of Mn7+ to Mn2+, the oxygen in the hydrogen peroxide must undergo oxidation.
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" "
13
"
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G10 Chemistry: Making Useful Materials Electrolysis – Extracting Aluminium
Aluminium ore is called bauxite. Bauxite contains aluminium oxide, water, iron oxide and other impurities. The purified dry ore, called alumina, is aluminium oxide – Al2O3 Unfortunately, alumina has a high melting point (2040 °C) and it is not practical to do electrolysis at such a high temperature. In the middle of the nineteenth century it was found that alumina dissolved in cryolite. A solution of alumina in cryolite melts at about 900 °C and electrolysis is done at about 950 °C.
The steel container is coated with carbon (graphite) and this is used as the negative electrode (cathode). Aluminium oxide (Al2O3) is an ionic compound. When it is melted the Al3+ and O2- ions are free to move and conduct electricity. Electrolysis of the alumina/cryolite solution gives aluminium at the cathode and oxygen at the anode.
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G10 Chemistry: Making Useful Materials Electrolysis – Extracting Aluminium
a) Complete the half equation for the reaction at the cathode;
, $
,
b) Is this an example of oxidation or of reduction?
c) Complete the half equation for the reaction at the anode;
"
"
d) Is this an example of oxidation or reduction?
Aluminium is more dense than the alumina/cryolite solution and so it falls to the bottom of the cell where it can be tapped off as pure liquid metal. Oxygen is given off at the positive carbon anode. Carbon dioxide is also given off at the carbon anode because hot oxygen reacts with the carbon anode to form carbon dioxide gas. Because of this the carbon anodes slowly disappear, so the carbon anodes need to be replaced when they become too small.
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G10 Chemistry: Making Useful Materials Electrolysis - Copper
The anode is a block of impure copper. The cathode is a thin piece of pure copper. When electricity is passed through the cell copper is dissolved at the anode and Cu2+ ions go into solution. a) Complete the half equation at the anode;
"
b) Cu2+ ions are formed. Is this an example of oxidation or reduction? c) At the cathode, copper is deposited. Complete the half equation;
"
d) Cu metal is formed. Is this is an example of oxidation or reduction? As copper ions move from the anode to the cathode the anode gets smaller as the cathode gets bigger. This is a redox reaction.
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G10 Chemistry: Making Useful Materials Electrolysis - Copper
Complete these sentences.
The rate at which the copper ions enter the electrolyte from the anode is ________________________________ as the rate at which the copper ions leave the electrolyte at the cathode.
The concentration of the copper(II) sulfate solution therefore remains _______________________________.
As copper is transferred from the anode to the cathode any soluble impurities in the copper anode ______________________________ in the copper(II) sulfate and are removed later.
____________________________________ impurities fall to the bottom of the cell and form a sludge. The sludge often contains precious metals ( such as ___________________________ and ______________________________ ) which are extracted and refined.
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G10 Chemistry: Making Useful Materials Electroplating
The metal plating process (also called electroplating) uses electrolysis of a solution containing ions of the plating metal. Most metals can be plated. Common plating metals are gold, nickel and silver as well as chromium and zinc. The anode is made from the pure plating metal. The metal object which needs plating is used as the cathode.
a) When electricity is passed through the cell silver is dissolved at the anode. Ag+ ions go into the silver nitrate solution. Complete the reaction for the anode;
,
,
b) Silver ions are formed. Is this an example of oxidation or reduction? c) Silver is deposited onto the surface of the object at the cathode. Complete the reaction for the cathode;
,
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G10 Chemistry: Making Useful Materials Electroplating
d) Silver metal is formed. Is this an example of oxidation or reduction? e) As silver ions move from the anode to the cathode the anode gets smaller as the object becomes silver plated. f)
Complete these sentences for this redox reaction. The rate at which the silver ions enter the electrolyte from the anode is ________________________________as the rate at which the silver ions leave the electrolyte at the cathode.
The concentration of the silver(II) nitrate solution therefore remains _________________________________.
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G10 Chemistry: Making Useful Materials Sacrificial Protection
Sacrificial protection is used for ships, under water pipelines and oil rigs (for example in the North Sea). Blocks of a more reactive metal (for example magnesium or zinc) are attached to the ship's hull or the under water pipe. The magnesium or zinc can also be connected to a pipeline or oil rig by conducting cables. Sacrificial protection is similar to a displacement reaction with the electrons travelling from the more reactive metal to the steel either directly or through the conducting cable.
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G10 Chemistry: Making Useful Materials Sacrificial Protection
The use of sacrificial metals reverses the rusting process. a) Complete the half equation for Zinc;
- "
-
b) Is Zinc is oxidised or reduced as it dissolves? c) Complete the half equation for Iron;
! $
!
d) Are the Iron ions oxidised or reduced to iron atoms? Rusty steel is returned to iron metal. The block of zinc or magnesium is sacrificed to keep the steel from rusting and must be replaced before it all dissolves. This is less expensive than rebuilding the ship or replacing the pipe or oil rig.
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G10 Chemistry: Making Useful Materials Practice Question 1
Two experiments were set up as shown. Experiment C
Experiment D
Solid sodium chloride (Na + Cl – )
Molten sodium chloride + – (Na Cl )
Heat
a) Give two observations which would be seen only in Experiment D. b) Explain why in Experiment C no changes would be seen. c) Another electrolysis experiment used an aqueous solution of copper chloride.
Experiment E
Deposit B Gas A Solution of copper chloride Name the gas A and the deposit B.
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G10 Chemistry: Making Useful Materials Practice Question 2
A student investigated the electrolysis of lead bromide.
Tube Electrodes Lead bromide (toxic)
Lead bromide
Heat Lead bromide was placed in the tube and the circuit was switched on. The light bulb did not light up. The tube was heated and soon the bulb lit up. The observations are shown in the table. Positive electrode
Negative electrode
red-brown gas
silver liquid
a) What is meant by electrolysis? b) Why did the lead bromide conduct electricity when the tube was heated? c) Name the substances formed at the: i)
positive electrode;
ii)
negative electrode. 2)
d) Suggest one safety precaution that should be taken during this investigation.
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G10 Chemistry: Making Useful Materials Practice Question 3
An investigation into the electrolyte copper sulphate solution was carried out as shown.
Copper sulphate solution
Carbon electrodes
+
–
a) What does electrolyte mean? b) These were the observations.
i)
Negative electrode
solid formed
Positive electrode
gas given off
Name the solid formed.
ii) Name the gas given off. c) How could a sample of gas be collected at the positive electrode? d) Suggest why the blue colour of copper sulphate becomes paler during the investigation.
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G10 Chemistry: Making Useful Materials Practice Question 4
a) Copper is a widely used metal. The main ore of copper contains copper sulfide. Copper can be extracted from copper sulfide in a three stage process. i)
In the first stage of extraction the copper sulfide is heated in air.
Balance the symbol equation for the reaction.
ii)
Explain why there would be an environmental problem if the gas from this reaction were allowed to escape into the atmosphere.
b) In the second stage copper oxide, CuO, is reduced using carbon. Write a balanced symbol equation for this reaction. c) During the third stage the copper can be purified as shown in the diagram.
i)
What is the name of the type of process used for this purification? purificat
ii)
Give one use of purified copper.
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G10 Chemistry: Making Useful Materials Practice Question 13
Global warming is thought to be happening because of the increased burning of fossil fuels. The concentration of carbon dioxide in the air from 1905 to 2005 has been calculated. 380 370 360 350 Concentration 340 of carbon dioxide in ppm 330 320 310 300 290 280 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 Year
a) Draw a line of best fit for these points. b) What was the concentration of carbon dioxide in 1955? c) In what year did the concentration of carbon dioxide reach 350 ppm? d) Use the graph to describe, in as much detail as you can, what happened to the concentration of carbon dioxide from 1905 to 2005.
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G10 Chemistry: Making Useful Materials Electrochemistry Revision 1
For each of the circuits below, decide if the ammeter will show that a current is flowing. If it does conduct, state what is carrying the current in the beaker. For ions, give their symbols.
A
A
Zinc chloride solution
Solid zinc chloride
A
A
Molten zinc chloride
Molten zinc
A
A
Hexane C6 H14
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Hydrochloric acid
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G10 Chemistry: Making Useful Materials Electrochemistry Revision 2 & 3
Question 2 In each of the following equations, decide if the underlined substance is being oxidized, reduced or neither. 2 Na
Si
+
+
K N
2
+
Cl 2
2 NaCl
Cl 2
SiO
+ K 3H 2
+
2
e 2NH . 3
Question 3 The picture shows the apparatus used in the extraction of aluminium a) What are the parts labelled A to E?
b) Give equations for the reactions that take place at each electrode. c) What is aluminium ore called? d) Aluminium oxide has a very high melting point. How is it made lower?
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G10 Chemistry: Making Useful Materials Electrochemistry Revision 4 & 5
Question 4 Give equations for the reactions that take place at each electrode when each of the following liquids is electrolysed. All reactions are with graphite electrodes unless otherwise stated. a) Molten lead (II) bromide
b) Sodium chloride solution
c) Dilute sulfuric acid
d) Silver (I) nitrate solution with silver electrodes.
Question 5 a) Describe a test you could carry out to find out if a substance is an oxidizing agent.
b) Describe a test you could carry out to find out if a substance is a reducing agent.
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G10 Chemistry: Making Useful Materials Electrochemistry Revision 6-8
Question 6 The picture shows some acid being electrolysed. What are the gases A and B?
Question 7 Draw a diagram to show how copper is purified. Give equations for the reactions at each electrode.
Question 8 The picture below shows an electric circuit. Without changing the power supply, give 3 changes you could make which would increase the reading on the ammeter.
A
NaCl solution
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G10 Chemistry: Making Useful Materials Redox Revision Questions
1) Give 3 descriptions of reduction. 2) Decide if the underlined element has been oxidized, reduced or neither: a) CH + 2O → CO + 2H O 4 2 2 2 b) Mg + H SO → MgSO + H 2 4 4 2 + − c) 2H + 2e → H 2 d) CuO + 2HCl → CuCl + H O 2 2
3) Write equations for the reactions that take place at each electrode when the following liquids are electrolysed (graphite electrodes unless otherwise stated). a) NaCl (aq) b) NaCl (l) c) Al O (l) 2 3 d) CuSO (aq) copper electrodes 4 e) AgNO (aq) 3
4) Describe a test for an oxidizing agent.
5) Draw and label a diagram of the circuit you would use to plate a cup with nickel.
6) This question is on aluminium extraction. a) What is the ore from which we get aluminium. b) Cryolite is put in the electrolytic cell. Why? c) What happens to the oxygen that is given off at the anode?
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G10 Chemistry: Making Useful Materials Organic Chemistry
Organic chemistry is the chemistry of carbon based compounds. This is an extremely significant category of chemicals. All living things (like you) and substances made from things that were living (such as coal, crude oil and natural gas) are organic compounds. Remember that Carbon ( C ) is in Group IV of the Periodic Table, so it forms four (covalent) bonds with other chemicals, like Hydrogen. Organic compounds that are made of only carbon and hydrogen are called Hydrocarbons. Look at the hydrocarbon molecules shown in the pictures, which show 3 of the simplest possible hydrocarbons. Notice that there are four “single bonds� for each carbon atom and that each hydrogen atom has one single bond.
These are the first 3 in a series of related compounds called alkanes. The first one is called methane and has a formula CH4. The second alkane has a formula of C2H6. It could also be written as CH3-CH3 or just CH3CH3. These alternative ways of writing the alkane are very useful because they give more information about the structure of the substance. In the same way the third alkane would normally be given the formula C3H8. It can also be written as CH3-CH2-CH3 or just CH3CH2CH3.
Exercise. What is the structure and formula for the next member of the alkane family (butane, containing 4 carbon atoms)? How can the formula also be written?
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G10 Chemistry: Making Useful Materials Alkanes
Many of the alkanes are common compounds. For example methane is used in Science laboratories in Bunsen burners and Propane is used as camping gas. Complete the table for the first 10 alkanes below and deduce the general formula for an alkane containing N carbon atoms. Name
Number of Carbons
Formula
Methane
1
CH4
Ethane
2
C2H6
Propane
3
C3H8 C4H10
Butane Pentane Hexane Heptane Octane Nonane Decane ----
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N carbons
33
CN H
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G10 Chemistry: Making Useful Materials Alkanes
We can keep adding extra carbon atoms to get longer and longer alkane compounds. However, when we get to Butane (4 carbon atoms and 10 hydrogen atoms), we can also begin to arrange them in different ways, like this:
And like this:
The middle carbon is now attached to 3 other carbons. These are different molecules with the same formula (C4H10) are called isomers.
Exercise Try drawing some isomers of pentane ( C5H12) yourself. Note: the molecule shown below is not a new isomer, it still has 4 carbons in a line, we have simply bent the molecule round.
The alkanes are known as saturated hydrocarbons because all of the available bonds to carbon atoms are occupied with hydrogen atoms. They are relatively unreactive, apart from combustion with oxygen. For this reason they are common fuels. Methane gas is used for cooking (and in Science laboratories). Propane and Butane are used as camping gas. Larger compounds like octane are present in petrol used in cars and motorcycles.
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G10 Chemistry: Making Useful Materials Combustion of Alkanes
All alkanes will burn in oxygen to produce carbon dioxide and water. Question 1 Balance these equations for the combustion of some alkanes. CH4
+
O2
CO2
+
H2O
C2H6
+
O2
CO2
+
H2O
C3H8
+
O2
CO2
+
H2O
C4H10
+
O2
CO2
+
H2O
Question 2 What would the products be if there was insufficient oxygen for complete combustion?
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G10 Chemistry: Making Useful Materials Crude Oil
Oil that we get from the ground, in oil wells, is called crude oil. It is a mixture of lots of different alkanes – from 1 carbon atom (CH4) to over 70 carbon atoms. In order to make use of crude oil it first needs to be separated into groups of similar compounds and this process is called fractional distillation. This process is summarised below. Crude oil is heated up to high temperatures, causing most of the alkanes in the crude oil to boil. This boiling mixture enters the base of the fractionating column. The gases formed rise up and so cool down. Compounds with more carbon atoms condense sooner while the lighter compounds rise further up the column. In this way groups of alkanes with a similar number of carbon atoms, or fractions, can be collected.
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G10 Chemistry: Making Useful Materials Crude Oil
Make a table like the one shown below to summarise the uses of the various fractions of crude oil. Useful sites for your research might include; http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/rocks/fuelsrev1.shtml
http://www.chemguide.co.uk/organicprops/alkanes/background.html#top . Name of Fraction
Number of Carbons
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Description & Uses
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G10 Chemistry: Making Useful Materials Cracking
In the fractional distillation process, many of the alkanes that are obtained are long chains – such as those in the lubricating oil, fuel oil and bitumen fractions. In order to make these long chained hydrocarbons more useful they can be cracked into smaller compounds. The cracking of alkane hydrocarbons involves thermal decomposition. This means that the large hydrocarbon molecules break into smaller molecules when they are heated. The hydrocarbons are boiled and the hydrocarbon gases are passed over a hot powdered aluminium oxide (Al2O3) catalyst. The catalyst works by providing a good surface for the cracking to take place.
Example 1 Decane is an alkane containing 10 carbon atoms (C10H22). This can be cracked to produce a smaller alkane called octane (C8H18) and a second product, ethene (C2H4). This last compound belongs to a different series called the alkenes and is itself a very useful chemical. C10H22
C8H18
+
C2H4
Notice that the equation balances automatically. Octane is used in petrol and ethene is used to make polymers.
Example 2 Hexane can be cracked to give ethene and one other product. a) Write a balanced equation for this reaction. b) Name the other product. c) Identify any saturated hydrocarbons in your reaction.
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G10 Chemistry: Making Useful Materials Alkenes
H
H
H
C
C
C
C
C
H
H
H
H
H
H
H
A second series of related hydrocarbons is obtained if we include one double bond between two of the carbon atoms. The simplest possible arrangement is shown on the left (notice that the simplest arrangement must have two carbon atoms) and is called ethene. The formula for ethene is C2H4. The next simplest arrangement, with three carbon atoms, is shown on the right and is called propene. The formula for propene is then C3H6. The series of chemicals that are formed by adding more carbons is called the alkenes. Notice the similarity of names compared to the alkane family. The difference is that all alkenes have names ending in –ene. As before we can also write the formulas for these alkenes in different ways. For example, the simplest alkene is ethene and is usually written as C2H4. We could also write this as CH2-CH2 or just CH2CH2. The next alkene in the series is propene, normally written as C3H6. We could write this to give more information as CH2-CH-CH3 or just CH2CHCH3.
Exercise. What would be the structure of the next alkene, butene, containing 4 carbon atoms?
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G10 Chemistry: Making Useful Materials Alkenes
One of the most significant uses of alkenes is to make polymers. These are amazingly common in just about every aspect of our lives today. Two examples are shown above – plastic bags are made from the polymerisation of ethene (to make poly(ethene) – usually called polythene) and other items like plastic folders are made from the polymerisation of propene (to make poly(propene) – usually called polypropylene). Complete the table below for the first few alkenes and deduce the general formula for an alkene containing N carbon atoms. Name
Number of Carbons
Formula
Ethene
2
C2H4
Propene
3
C3H6
Butene
4
C4H8
N carbons
CN H
Pentene Hexene Heptene Octene ----
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G10 Chemistry: Making Useful Materials Alkenes
H
H
C
C
C
H
H
CH3
H
C
C
H
H
H
C2H5
H
C
H
You can draw alkenes in the usual way. However, one particularly useful way of drawing them is shown above, which shows ethene (left), propene (middle) and butene (right). What has happened is that everything that comes after the second carbon atom has been placed together. This has the effect of making them all look similar, which will very useful when we look at polymerisation. Alkenes are more reactive than their alkane cousins – ethene is more reactive than ethane for example. This is because, in a reaction, the double bond may “break” and so allow a wider variety of combinations with other chemicals. Examples. The reaction of ethene with hydrogen can be written as; C2H4
+
H2
C2H6
And the reaction of ethene with chlorine could be written like this; CH2-CH2
+
Cl2
CH2Cl-CH2Cl
Exercises; Balance these reactions for the combustion of ethene and propene. C2H4
+
O2
CO2
+
H2O
C3H6
+
O2
CO2
+
H2O
C4H8
+
O2
CO2
+
H2O
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G10 Chemistry: Making Useful Materials Polymerisation
H
n
H
C
H
C
C
H
H
H
C
H
H
n n x ethene monomers
1 x poly(ethene ) polymer, n units long
The unique nature of alkenes – having a double bond between two of the carbon atoms – turns out to be very significant. In particular, it allows the possibility of making polymers. A polymer is formed when thousands of monomers (of a particular alkene) add together to make one very long molecule. One of best examples of this would be the addition of thousands of ethene molecules (the monomers) to make one poly(ethene) – or polythene – molecule. Polythene is the material that plastic bags are made of – like those you find at a supermarket. The reaction of ethene by addition polymerisation to make polythene is represented above. The n in the reaction represents a very large number, typically thousands. What happens is that the double bond in ethene unfolds, as shown in the diagram at the bottom. This makes two more connections available for each molecule, which are used to join to each other in one very long chain.
H
C
H
H
H
H
C
C
H
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H
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G10 Chemistry: Making Useful Materials Polymerisation
C6H5
H
C
C
H
H
Example The monomer styrene is used to make the polymer poly(styrene), often referred to as Styrofoam. The monomer is represented by the drawing above. Styrene undergoes addition polymerisation to form polystyrene. a) Represent the reaction of styrene to form polystyrene. Shown below. b) Give one use of polystyrene. For packaging electronic goods. c) Give one harmful effect that polystyrene can have on the environment. Polystyrene is not biodegradable. This can cause problems if it is not re-used or recycled. It could be burned to release energy but this may result in the production of toxic chemicals.
C6H5
H
n
C
H
C6H5
H
C
C
H
C
H
H
n
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G10 Chemistry: Making Useful Materials Organic Chemistry Checklist
1) The bonding of carbon – remember each carbon forms 4 bonds, each hydrogen forms 1 bond and each oxygen forms 2 bonds. E.g. H H
C
O
2) Isomers (different arrangements of the same atoms in a molecule) e.g. show the different isomers of pentane C5H12. 3) Saturated (no double or triple bonds) and unsaturated (at least one double or triple bond) e.g. alkanes are saturated and alkenes are unsaturated. 4) Homologous series (a group of compounds with the same general formula, the same chemical properties and a steady change in some physical properties such as boiling point). The members of a homologous series have the same functional group e.g. the C=C double bond in alkenes and the –OH group in alcohols. 5) Alkanes – you need to know their general formula – CNH2N+2 You need to know their names up to C10H22 (methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane). You need to know why they are relatively unreactive – in order to react, they must break strong C-C and C-H bonds. 6) Revise the fractional distillation of crude oil, how it works and the way their different boiling points allows us to separate them, ways in which the fractions differ plus uses for some fractions. 7) Be able to write and balance equations for combustion (burning, reacting with oxygen). 8) Be able to describe cracking (using heat and/or catalysts to turn bigger less useful molecules into smaller, more valuable ones). Remember, cracking always produces unsaturated compounds. 9) Alkenes – you need to know their general formula – CNH2N You need to know their typical reaction – addition to the double bond; The test for alkenes – they decolourise bromine water from orange/brown; preparing alkenes – see cracking; making polymers (plastics) from alkenes and other unsaturated compounds. 10) Advantages and problems caused by the use of plastics and crude oil.
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G10 Chemistry: Making Useful Materials Practice Question 1
Propane and ethene are both important hydrocarbons.
propane formula
ethene
C3H8 H
H C
structure H
C H
a) Copy and complete the table by adding the formula of the ethene molecule and the structure of the propane molecule. b) Propane is a fuel used in camping stoves. When propane burns there is an exothermic reaction. What is meant by the term “exothermic reaction�? c) Balance the chemical equation for the reaction which takes place when propane burns in a plentiful supply of air. C3H8
+
O2
CO2
+
H2O
d) Ethene can be changed into a plastic. The equation shown below represents the reaction in which ethene is polymerised.
n
H
H
H
H
C
C
C
C
H
H
H
H n
i)
What is the name of the plastic formed in this reaction?
ii)
What type of polymerisation reaction is shown in the equation?
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G10 Chemistry: Making Useful Materials Practice Question 2
To make crude oil more useful it is separated into different fractions.
Refinery gas 40°C Petrol 110°C
180°C
260°C 350°C
Crude oil
Kerosene Gas oil Fuel oil
400°C
Over 400°C
Heat
a) Complete the gaps in the following sentences. Crude oil is separated into different fractions by a process called .............................................. ……………................................... . Each fraction has a different ............................................... b) Each fraction is a mixture of compounds. Most of these compounds are hydrocarbons, made up of the elements hydrogen and carbon. i)
Explain the difference between a mixture and a compound.
ii)
Explain the difference between a compound and an element.
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G10 Chemistry: Making Useful Materials Practice Question 3
One reason the oil industry is important is that it uses crude oil to produce many of the plastic materials we use in everyday life. a) The first stage in the formation of a plastic material is called cracking. Butane (C4H10) a hydrocarbon in crude oil, can be cracked to produce two different hydrocarbons, ethane (C2H6)) and ethene (C2H4) For cracking to happen what needs to be done to the hydrocarbon? b) Copy and complete the equation for the cracking of butane using displayed formulae.
H
H
H
H
H
C
C
C
C
H
H
H
H
+
H
Butane (C4H10)
Ethane (C 2 H 6 )
Ethene (C 2 H 4 )
c) Copy and complete the balanced chemical equation far the complete combustion of ethane in oxygen. C2H6
+
…………………..
…………………….
+
…………………….
d) The second stage is the formation of the plastic material by polymerisation. Describe how ethene (C2H4) forms poly(ethene). You do not need to give the reaction conditions or the names of catalysts.
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G10 Chemistry: Making Useful Materials Practice Question 4 & 5
Question 4 The diagram shows a reaction which takes place in an oil refinery.
H
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
Compound X
H
H
H
H
H
H
H
C
C + H
C
C
C
C
H
H
H
H
H
H
Compound Y
H
Compound Z
a) X, Y and Z are all examples of which type of compound? b) What type of chemical reaction takes place when compound X is converted into compounds Y and Z? c) Compounds Y and Z are both useful substances. Compound Y is unsaturated. Compound Z is saturated. i)
Explain what is meant by the terms “saturated” and “unsaturated”.
ii)
Suggest one use for compound Y.
i)
Suggest one use for compound Z.
Question 5 a) Crude oil consists of a large number of different compounds. Most of these compounds are alkanes. Explain how fractional distillation separates crude oil. b) What are alkanes? c) Alkanes, such as methane, CH4, are used as fuels. Write a balanced chemical equation for the complete combustion of methane in oxygen. d) Alkenes can be made by cracking large alkane molecules. Explain how the cracking process is carried out. e) Give a chemical test which would show the difference between an alkene and an alkane
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G10 Chemistry: Making Useful Materials Practice Question 6
The label has been taken from a tube of Humbrol Polystyrene Cement, a glue used in model making.
HUMBROL Polystyrene Cement Paint product contains 1.1.1 TRICHLOROETHANE • Keep container tightly closed. HARMFUL
Harmful by inhalation, in contact with skin and if swallowed. Avoid contact with eyes. Keep out of reach of children.
• For use on all polystyrene plastic except expanded or foam. Specially recommended for plastic kits. Thinly coat each surface, press together. To remove cement from fabrics use Humbrol Universal Cleaner.
HUMBROL LTD., HULL, ENGLAND.
a) The solvent used is 1,1,1-trichloroethane. The structural formula of this molecule is:
Cl
Cl
H
C
C
Cl
H
H
b) What do the lines between the atoms represent? c) State whether 1,1,1-trichloroethane is saturated or unsaturated. Give one reason for your answer. d) 1,1,1-trichloroethane is being replaced in favour of a ‘better’ solvent. Use information on the label to help you to suggest why.
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G10 Chemistry: Making Useful Materials Practice Question 7
Polystyrene is a plastic. Plastics are polymers which are made by the process of polymerisation. a) What is meant by polymerisation?
b) The table gives information about monomers and the polymers made from them. Complete the table.
POLYMER
MONOMER name ethene
formula H
name H
C
C
H
H
styrene
polystyrene
formula H H C
C
H
H
H
H
C
C
H chloroethene
H
H C
H
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C 6H 5 n
poly(chloroethene)
C Cl
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G10 Chemistry: Making Useful Materials Practice Question 8
a) Ethene is the starting material for two plastics, poly(ethene) and PVC. Give one use for each of these plastics. i)
Poly(ethene)
ii)
PVC
b) Crude oil is a mixture of many compounds. Most of the compounds consist of molecules made only of carbon and hydrogen. Choose one word from the list below to complete the sentence. carbohydrates
carbonates
hydrocarbons
hydrogen-carbonates
c) What name is given to compounds made only of carbon and hydrogen? d) The fractions contain molecules with similar numbers of carbon atoms. The main fractions are shown in the table below.
petroleum gases
NUMBER OF CARBON ATOMS IN MOLECULES 1 to 4
gasoline
4 to 12
naphtha
7 to 14
kerosene
11 to 15
diesel oil
14 to 19
lubricating oil
18 to 30
residue
more than 30
NAME OF FRACTION
Naphtha burns more easily than diesel oil. Explain why.
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G10 Chemistry: Making Useful Materials Practice Question 9
Propane is a small, hydrocarbon molecule and it is used as a fuel.
H
H
H
H
C
C
C
H
H
H
H
Propane molecule
Propane gas
a) Complete the sentences by choosing the correct words from the box. carbohydrate
high
hydrogen
hydroxide
low
volatile
Propane is a hydrocarbon with a ................................................................ boiling point. Propane is a hydrocarbon because it is made of ........................................................ and carbon only. b) Describe, in as much detail as you can, what happens when propane burns.
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G10 Chemistry: Making Useful Materials Practice Question 10
Crude oil is a complex mixture of hydrocarbons, mainly alkanes. The number of carbon atoms in the molecules ranges from 1 to over 100. a) How does the boiling point change as the number of carbon atoms in the molecules increases? b) Name the method used to separate petroleum into fractions. c) The simplest hydrocarbon is methane, CH4. Its structure can be represented: H H
C
H
H
Draw the structure of ethane, C2H6. d) Large hydrocarbon molecules are less useful as fuels. They can be broken down to give smaller molecules. Some of these smaller molecules are unsaturated. The simplest of these is ethene, C2H4. i)
Name the process used to break down large hydrocarbon molecules.
ii)
Draw the structure of ethene, C2H4.
iii)
Why is ethene said to be unsaturated?
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G10 Chemistry: Making Useful Materials Practice Question 11
Cracking is an important process in the oil industry. The equation below shows the cracking of a hydrocarbon compound into two different compounds, A and B.
H
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
C
C + H
C
C
C
C
H
H
H
H
H
H
Compound A
H
Compound B
a) State two differences between the structures of compounds A and B.
b) Name compounds A and B
c) Why is compound A useful in industry?
d) Alkanes and alkenes are obtained from crude oil. What method is used to separate crude oil into its components?
e) The box contains the names of five components that can be separated from crude oil diesel
fuel oil
paraffin
petrol
propane gas
Write the list in order of increasing boiling point, starting with the lowest boiling point.
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G10 Chemistry: Making Useful Materials Practice Question 12
Read the following information.
Landfill, Incineration, Recycling and Re-use of Poly(ethene)
People could be encouraged to re-use their poly(ethene) bags and containers.
Recycling poly(ethene) saves raw materials and energy needed to make new plastic. When polymers are recycled the plastics must be collected, transported, sorted into different types by hand and washed. This requires the use of fossil fuels and is expensive.
Poly(ethene) can be burnt in an incinerator with other household waste. The heat released could be used to make steam to drive an electric generator. Surplus heat could be used to heat greenhouses used for growing vegetables. Incineration at too low a temperature can produce harmful substances. The residue (ash) has to go to landfill.
Landfill is probably the easiest way to dispose of polymers and it is cheap. Polymers are often mixed in with other household rubbish. Household waste does not get sorted into different materials because it is disposed of in the same hole in the ground. When the hole is eventually full, the waste is covered by a layer of soil to stop it smelling. The waste gets compressed under its own weight. Most polymers, such as poly(ethene), are not biodegradable so will remain in the ground forever.
a) You are asked to decide which option for the disposal of poly(ethene) will be put forward in your area. You decide that recycling is the best option. Suggest one economic argument and one environmental argument that will be made against recycling.
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G10 Chemistry: Making Useful Materials Practice Question 13
Global warming is thought to be happening because of the increased burning of fossil fuels. The concentration of carbon dioxide in the air from 1905 to 2005 has been calculated. 380 370 360 350 Concentration 340 of carbon dioxide in ppm 330 320 310 300 290 280 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 Year
e) Draw a line of best fit for these points. f)
What was the concentration of carbon dioxide in 1955?
g) In what year did the concentration of carbon dioxide reach 350 ppm? h) Use the graph to describe, in as much detail as you can, what happened to the concentration of carbon dioxide from 1905 to 2005.
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G10 Chemistry: Making Useful Materials Organic Revision 1
Cracking is used in the oil industry to break large hydrocarbon molecules into smaller molecules.
Small molecules out
Reactor vessel containing catalyst
Large molecules in a) Cracking involves a thermal decomposition reaction. State what must be done to make a thermal decomposition take place. b) Suggest why air must be excluded from the reactor vessel. c) The equation shows a reaction that can take place in the reactor vessel. A nonane molecule is split into two smaller molecules. Complete the equation by adding the formula of the other product. C9H20
………………………………….. +
C2H4
d) The product with the formula C2H4 is called ethene. Some ethene is reacted with steam. The equation represents this reaction. C2H4
+
H2O
C2H5OH
Name the useful product with the formula C2H5OH.
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G10 Chemistry: Making Useful Materials Organic Revision 2
Modern window frames are often made from uPVC plastic which contains the polymer called poly(chloroethene).
+
WONDERFUL WINDOWS Replace your old wooden windows with our superb high quality uPVC windows! NO PAINTING - MAINTENANCE FREE
a) State why plastic window frames need no painting or maintenance. b) Name the monomer that is used to make poly(chloroethene). c) Explain what is meant by the term polymer. d) Give one disadvantage of using a polymer for window frames. e) The monomer used for making the polymer uPVC is often called vinyl chloride. It has a structure that is similar to ethene except that one of the hydrogen atoms in ethene is substituted by a chlorine atom. Draw structures to represent ethene and vinyl chloride.
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G10 Chemistry: Making Useful Materials Organic Revision 3
The diagram shows an apparatus that can be used to carry out cracking reactions in a laboratory. Paraffin soaked onto mineral wool Aluminium oxide or broken porcelain Delivery tube
B Strong heat
Warm
A
Cold water
a) Why is aluminium oxide or broken porcelain used? b) Paraffin contains decane. The cracking of decane can be represented by the equation below. A decane molecule is split into two smaller molecules. Complete the equation by adding the formula of the other product. C10H22
……………………………………..
+
C2H4.
c) Would you expect C2H4 molecules to collect at position A or B shown on the diagram? Explain your answer. d) Explain, as fully as you can, why cracking is used in the oil industry. e) The cracking reaction produces a mixture of products. The mixture contains hydrocarbons with different boiling points. Suggest a method of separating this mixture.
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G10 Chemistry: Making Useful Materials Organic Revision 4
a) Propene and propane can be produced from crude oil. A propene molecule (C3H6) can be represented by the structure shown below.
H C
H
H
C
C
H
H
H
Draw a similar diagram to show the structure of a propane molecule (C3H8) b) Which molecule, propene or propane, is unsaturated? Give a reason for your answer c) The equation below represents the polymerisation of propene.
H
H
H
H
n C
C
C
C
H CH 3
H CH 3 n
Name the polymer produced by this reaction. d) Explain the meaning of the term polymerisation. e) Describe the problems caused by the everyday use of this polymer.
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