Fuels — Paper 4 · IGCSE Science - Combined 0653

2 (a) Fig. 2.1 is a dot-and-cross diagram to show the outer-shell electrons in a molecule of hydrogen chloride, HCl. X X X X H Cl X X X Fig. 2.1 (i) State the type of chemical bond shown in Fig. 2.1. … [1] (ii) Draw a dot-and-cross diagram to show the outer-shell electrons in a molecule of methane, CH4. [2] (b) (i) Name the two products of the complete combustion of methane. 1. … 2. … [2] (ii) Explain, in terms of energy changes, why methane is used as a fuel. … … [1] (c) Methane is the main constituent of one fossil fuel. (i) State the name of this fossil fuel. … [1] (ii) State the names of two other fossil fuels. … and … [1]

8 marks

Mark scheme: 2(a)(i) 1 2(a)(ii) four shared pairs between C and four H atoms ; all symbols correctly shown ; 2 2(b)(i) carbon dioxide ; water ; 2 2(b)(ii) releases heat / thermal energy when it reacts / burns / is used ; 1 2(c)(i) natural gas ; 1 2(c)(ii) coal and petroleum ; 1

This question in 0653/41 May/June 2017

5 Fractional distillation of petroleum produces fractions containing different compounds. C3H8 process Y C5H12 C16H34 strong heat hot petroleum Fig. 5.1 (a) The formulae of three compounds contained in three fractions are shown in Fig. 5.1. Describe the trend in the boiling points of these three compounds, from C3H8 to C16H34. Explain this trend in terms of the sizes of the molecules and the forces between the molecules. trend … explanation … … … [3] (b) Process Y, shown in Fig. 5.1, changes the molecules in one fraction. The molecular structure of a hydrocarbon produced in process Y is shown in Fig. 5.2. H H C C H H Fig. 5.2 (i) Name process Y. … [1] (ii) Name the hydrocarbon shown in Fig. 5.2. … [1] (iii) Name this type of hydrocarbon. … [1] (iv) State the colour change that is seen when this hydrocarbon is added to bromine water. from … to … [1] (c) The combustion of a fossil fuel is an exothermic reaction. Explain why this is an exothermic reaction. Use ideas about temperature change and energy transformation in your answer. … … … [2]

9 marks

Mark scheme: 5(a) (trend) increase (in boiling point) ; (explanation) bigger molecules ; greater intermolecular forces ; 3 5(b)(i) cracking ; 1 5(b)(ii) ethene ; allow ethylene 1 5(b)(iii) alkene / unsaturated ; 1 5(b)(iv) (from) orange / brown (to) colourless / decolourises ; 1 5(c) chemical (energy) to thermal / heat (energy) ; and one from temperature increases ; thermal energy (heat) released ; max 2

This question in 0653/43 Oct/Nov 2017

8 Petroleum is a fossil fuel. (a) (i) Name two other fossil fuels. 1. … 2. … [1] (ii) Name the industrial process used to separate the substances in petroleum. … [1] (b) The structures of two hydrocarbon molecules are shown in Fig. 8.1. H H H H H H H H H H C C C H H C C C C C C H H H H H H H H H H A B Fig. 8.1 (i) Construct the balanced symbol equation for the complete combustion of hydrocarbon A. … [2] (ii) State the formula of hydrocarbon B. … [1] (iii) State which of these two hydrocarbons has the higher boiling point. Explain your answer. hydrocarbon … explanation … … … [2] (c) The formula of hydrocarbon C is C2H4. (i) Name the process used to manufacture hydrocarbon C from larger hydrocarbon molecules. … [1] (ii) Draw the dot-and-cross diagram to show the bonding electrons in a molecule of hydrocarbon C. C C [2]

10 marks

Mark scheme: 8(a)(i) coal and natural gas ; 1 8(a)(ii) fractional distillation ; 1 8(b)(i) C3H8 + 5O2 → 3CO2 + 4H2O all formulae correct ; correct balancing (dependant on correct formulae) ; 2 8(b)(ii) C6H14 ; 1 8(b)(iii) (B / C6H14 / hexane) (B) larger molecule / surface area ; (B) greater intermolecular (attractive) forces / more energy needed to separate molecules ; 2 8(c)(i) cracking ; 1 Question Answer Marks 8(c)(ii) (circles not essential) double bond between carbon atoms ; four H atoms drawn with single pair between each and a C atom ; 2 Question Answer Marks 9(a) fuse in main circuit ; heating elements in parallel with each other and supply ; motor in parallel with heating elements (and supply) ; switches in series with both heaters and motor ; 4 9(b) total power supply required = 1200 × 2 + 100 = 2500 W ; use of P = I × V e.g. current through one heater = 5 A / total current = 2500 ÷ 240 ; = 10.4 A (which is above fuse rating) ; 3 Question Answer Marks 9(c) value within range 10–15 kHz ; top end of normal range is 20 kHz / older residents can hear up to 15 kHz ; 2

This question in 0653/43 May/June 2018

8 Useful substances are obtained from petroleum using the processes shown in Fig. 8.1. fractional process Y distillation fraction P column mixture containing alkenes strong heat petroleum fraction Q Fig. 8.1 (a) Compare the sizes of the molecules and the strengths of the intermolecular attractive forces between molecules in fraction P and in fraction Q. sizes of molecules … … intermolecular attractive forces … … [2] (b) Fraction P contains propane, C3H8. Construct the balanced equation for the complete combustion of propane. … [2] (c) Process Y produces alkene molecules from large alkane molecules. (i) State how the molecular structure of alkenes differs from the molecular structure of alkanes. … … [1] (ii) Describe a chemical test that is used to distinguish between propane and propene. State the observation for propane and for propene. test … propane observation … … propene observation … … [2]

7 marks

Mark scheme: 8(a) (size of molecules) P smaller than Q / ora ; (intermolecular forces) P smaller than Q / ora ; 2 8(b) C3H8 + 5O2 → 3CO2 + 4H2O species ; balancing ; 2 8(c)(i) alkenes have (one) (carbon-carbon) double bond / C=C ; or alkanes have only (carbon-carbon) single bonds / C-C ; 1 8(c)(ii) (test) (add) bromine (water) / Br2 ; (propane) no (visible) change and (propene) decolourises ; 2

This question in 0653/41 Oct/Nov 2018

2 Catalytic cracking breaks down large saturated hydrocarbon molecules into smaller hydrocarbon molecules. This process produces some unsaturated hydrocarbon molecules. (a) State what is meant by the term hydrocarbon. … … [1] (b) Fig. 2.1 shows apparatus used for catalytic cracking. reaction vessel catalyst saturated mixture of saturated and hydrocarbons unsaturated hydrocarbons Fig. 2.1 (i) State one other reaction condition, apart from a catalyst, used in the reaction vessel. … [1] (ii) Cracking is an endothermic reaction. Describe what is meant by an endothermic reaction. Use ideas about chemical energy and thermal energy in your answer. … … … … [2] (iii) Describe how aqueous bromine is used to show that this cracking process produces unsaturated hydrocarbons from saturated hydrocarbons. … … … … [2] (c) One of the products of cracking hydrocarbons is propene, C3H6 . (i) Complete the diagram in Fig. 2.2 to show the structure of one molecule of propene. H C Fig. 2.2 [3] (ii) Construct the balanced symbol equation for the complete combustion of propene. … [2] [Total: 11]

11 marks

Mark scheme: 2(a) molecule / compound containing carbon and hydrogen atoms only ; 1 2(b)(i) high temperature / high pressure ; 1 2(b)(ii) thermal energy is changed into chemical energy ; so thermal energy is absorbed / removed from surroundings / temperature (of surroundings) decreases ; 2 2(b)(iii) aqueous bromine remains orange / not decolourised by saturated hydrocarbons ; aqueous bromine is decolourised by unsaturated hydrocarbons ; 2 Question Answer Marks 2(c)(i) 3 carbon atoms in chain ; only one carbon-carbon double bond ; all else correct ; 3 2(c)(ii) 2C3H6 + 9O2 → 6CO2 + 6H2O all formulae correct ; balancing (dependent on correct formulae) ; 2

This question in 0653/42 May/June 2019

2 Hydrocarbons are composed of the two elements carbon and hydrogen. (a) State the type of chemical bond that forms between these two elements. Explain your answer. type of chemical bond … explanation … … … [2] (b) Cracking is a process used to make smaller alkene molecules from larger alkane molecules. (i) State two reaction conditions needed for cracking hydrocarbons. 1. … 2. … [2] (ii) During cracking, one molecule of decane, C10H22, breaks down to form one molecule of ethane, C2H6, and four molecules of another hydrocarbon. Complete the balanced symbol equation for the cracking of decane. … [1] C10H22 C2H6 + 4 (c) During the complete combustion of hydrocarbons, carbon dioxide and water are produced. (i) Draw a dot-and-cross diagram to show all of the outer shell electrons in the atoms in one molecule of carbon dioxide. [2] (ii) State one effect of an increase in the amount of carbon dioxide in the atmosphere. … … [1] [Total: 8]

8 marks

Mark scheme: 2(a) covalent ; bond between two non-metals ; 2 2(b)(i) heat / high temperature ; catalyst ; 2 2(b)(ii) (4) C2H4 ; 1 2(c)(i) one carbon atom and two oxygen atoms shown and correct electron distribution for carbon atom ; correct electron distribution for both oxygen atoms/lone pairs on both oxygen atoms ; 2 2(c)(ii) enhanced greenhouse effect / global warming / climate change / consequence of climate change ; 1

This question in 0653/41 Oct/Nov 2019

5 The structure of a molecule of ethene is shown in Fig. 5.1. H H C C H H Fig. 5.1 (a) State how Fig. 5.1 shows that ethene is an alkene. … [1] (b) Ethene is made from naphtha in an industrial process. Name this process. … [1] (c) Ethene undergoes a polymerisation reaction. (i) State the name of the polymer formed. … [1] (ii) State the type of polymerisation reaction that happens when ethene forms a polymer. … [1] (d) A student investigates the combustion of ethene. A cold surface is held near burning ethene. Drops of colourless liquid collect on the cold surface, as shown in Fig. 5.2. cold surface drops of colourless liquid burning ethene not to scale Fig. 5.2 (i) The student does a test which shows that the colourless liquid contains water. Describe a chemical test for water. State the colour change observed. test … colour change from … to … [2] (ii) During combustion, water forms as a gas. State the change that occurs when the gas collects as a liquid on the cold surface in Fig. 5.2. … … [1] (iii) State the name of the other product formed during the complete combustion of ethene. … [1] [Total: 8]

8 marks

Mark scheme: 5(a) (carbon-carbon) double bond ; 1 5(b) cracking ; 1 5(c)(i) poly(ethene) / polyethene ; 1 5(c)(ii) addition ; 1 Question Answer Marks 5(d)(i) (anhydrous) cobalt(II) chloride ; from blue to pink ; OR (anhydrous) copper(II) sulfate ; from white to blue ; 2 5(d)(ii) condensation / condenses ; 1 5(d)(iii) carbon dioxide ; 1

This question in 0653/43 May/June 2022

5 The energy level diagram for the combustion of hydrogen is shown in Fig. 5.1. energy B A hydrogen and oxygen C D water progress of reaction Fig. 5.1 (a) State which arrow, A, B, C or D, represents the overall energy change for the reaction. … [1] (b) Complete Table 5.1 to describe the changes represented by arrow A and arrow B. Place two ticks (3) in each row. Table 5.1 bonds bonds energy is energy is break form taken in given out arrow A arrow B [2] (c) Some cars use hydrogen as a fuel. Some cars use diesel oil as a fuel. Diesel contains mainly alkanes. (i) Give one similarity and one difference between the products of the combustion of hydrogen and of the complete combustion of alkanes. similarity … … difference … … [2] (ii) Use your answer to (c)(i) to suggest why diesel cars are considered more harmful to the environment than hydrogen cars. … … [1] (iii) Table 5.2 shows information about the melting points and boiling points of hydrogen and of diesel. Table 5.2 melting point / °C boiling point / °C hydrogen –259 –253 diesel less than 20 greater than 150 Use the information in Table 5.2 to suggest why hydrogen is more difficult to store than diesel at 20 °C. … … … … [2] [Total: 8]

8 marks

Mark scheme: 5(a) C ; 1 5(b) 2 bonds bonds energy is energy is break form taken in given out arrow A ✓ ✓ arrow B ✓ ✓ two or three correct ; all four correct ; 5(c)(i) similarity both produce, water / water vapour ; 2 difference alkanes / hydrocarbons / diesel, also produce carbon dioxide ; 5(c)(ii) (carbon dioxide emissions cause) 1 an enhanced greenhouse effect / contribute to climate change ; 5(c)(iii) hydrogen is a gas AND diesel is a liquid ; 2 hydrogen, takes up more space / needs to be stored under pressure ;

This question in 0653/41 Oct/Nov 2022

8 Cracking decane, C10H22, forms three compounds, as shown in Fig. 8.1. H H H H H H H H H H H C C C C C C C C C C H H H H H H H H H H H decane H H H H H H H H H H H C C C C C H + H C C C + C C H H H H H H H H H pentane propene ethene Fig. 8.1 (a) State which two compounds in Fig. 8.1 are alkanes. Give a reason for your answer. compounds … and … reason … … [2] (b) State two conditions needed for cracking. 1 … 2 … [2] (c) Describe what happens to the carbon-carbon bonds during cracking. … … … [2] (d) Refinery gas and naphtha are two fractions obtained from petroleum. Refinery gas contains some pentane. Naphtha contains some decane. Explain why pentane and decane are in different fractions. … … [1] (e) Refinery gas and naphtha have different uses. (i) State one use of refinery gas. … [1] (ii) Naphtha is used as a chemical feedstock. State the meaning of feedstock. … … [1] [Total: 9]

9 marks

Mark scheme: 8(a) decane and pentane ; reason: they are saturated (hydrocarbons) / do not contain double (C=C) bonds / contain only single bonds ; 2 8(b) any two from: high temperature ; high pressure ; catalyst ; 2 8(c) (some carbon – carbon single) bonds break ; (some) carbon atoms form double bonds (with each other) ; 2 8(d) they have different boiling points ; 1 8(e)(i) bottled gas / heating and cooking ; 1 8(e)(ii) (source / reactant for) making (other) chemicals ; 1

This question in 0653/42 May/June 2023

8 Cracking decane, C10H22, forms three compounds, as shown in Fig. 8.1. H H H H H H H H H H H C C C C C C C C C C H H H H H H H H H H H decane H H H H H H H H H H C C + H C C C C H + C C C C H H H H H H H H H H ethene butane butene Fig. 8.1 (a) State the two compounds shown in Fig. 8.1 that turn aqueous bromine colourless. Give a reason for your answer. compounds … and … reason … … [2] (b) State the name and formula of the two products formed in the complete combustion of decane. name … formula … name … formula … [2] (c) Name the homologous series that contains butane and decane. … [1] (d) State two reasons why cracking is described as a chemical change and not a physical change. 1 … 2 … [2] (e) The boiling points of butane and decane are shown in Table 8.1. Table 8.1 boiling point compound / °C butane –1 decane 174 (i) Explain why the boiling point of butane is lower than the boiling point of decane. Use ideas about forces in your answer. … … [1] (ii) Suggest one reason why propane and butane are in the same fraction obtained by fractional distillation of petroleum. … [1] [Total: 9]

9 marks

Mark scheme: 8(a) ethene and butene ; they both contain a double bond / are unsaturated / are alkenes ; 2 8(b) either order: carbon dioxide CO2 ; water H2O ; 2 8(c) alkanes ; 1 8(d) cannot be reversed by physical means ; new products formed ; 2 8(e)(i) butane has weaker forces between its molecules ; 1 8(e)(ii) similar boiling points ; 1

This question in 0653/43 May/June 2023

6 (a) Poly(ethene) is a polymer made from alkene monomers. (i) State the type of polymerisation reaction that forms poly(ethene) from its monomers. … [1] (ii) State the formula of the monomer used to make poly(ethene). … [1] (b) Name the process that produces alkenes from larger alkanes. … [1] (c) Table 6.1 shows statements about alkanes and alkenes. Put a tick (✓) in one box in each row to show whether each statement is true for alkanes only, true for alkenes only, or true for both. Table 6.1 true for true for true for alkanes alkenes both only only Four electrons are shared in a bond between two carbon atoms. The group of compounds have the same general formula. Complete combustion gives carbon dioxide and water. Adding aqueous bromine gives a colourless solution. [3] (d) Alkenes react with steam. Alkenes also react with hydrogen. Both reactions use a catalyst. (i) State the type of catalyst used in the reaction of alkenes with steam. … [1] (ii) Name the catalyst used in the reaction of alkenes with hydrogen. … [1] [Total: 8]

8 marks

Mark scheme: 6(a)(i) addition ; 1 6(a)(ii) C2H4 ; 1 6(b) cracking ; 1 6(c) 3 true for true for true for alkanes alkenes both only only A bond between two carbon ✓ atoms has four shared electrons. The group of compounds have ✓ the same general formula. Complete combustion gives ✓ carbon dioxide and water. Adding aqueous bromine ✓ ;;; gives a colourless solution. all four correct = 3 marks three correct = 2 marks two correct = 1 mark 6(d)(i) acid ; 1 6(d)(ii) nickel ; 1

This question in 0653/42 Feb/March 2025