Alkenes — Paper 4 · IGCSE Science - Combined 0653

8 (a) Methane, CH4, and butane, C4H10, are both alkanes. Methane boils at –162 °C. Butane boils at –1 °C. Explain this difference in terms of molecular size and intermolecular attractive forces. … … … … … [2] (b) Ethene, C2H4, is produced by a process that uses long-chain hydrocarbon molecules. (i) Name this process. … [1] (ii) A catalyst is used in this process. Describe the change, if any, to the catalyst at the end of this process. … [1] (c) Carbon dioxide is produced during the complete combustion of hydrocarbons. (i) State the formula of the other product of the complete combustion of hydrocarbons. … [1] (ii) Complete the dot-and-cross diagram to show the bonding electrons in carbon dioxide. O C O [1] (iii) State the type of chemical bond that forms between oxygen, a non-metal, and sodium, a metal. … [1]

7 marks

Mark scheme: 8(a) methane / CH4 is smaller (molecule) / has lower surface area ; methane / CH4 has weaker intermolecular forces / requires less energy to overcome intermolecular forces ; 2 8(b)(i) cracking ; 1 8(b)(ii) no change ; 1 8(c)(i) H2O ; 1 8(c)(ii) ; (oxygen non-bonding electrons not essential) 1 8(c)(iii) ionic / electrovalent ; 1

This question in 0653/42 Feb/March 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 separated into useful fractions by fractional distillation. Process Y produces short alkene molecules from longer alkane molecules. These processes are shown in Fig. 8.1. fractional process Y powdered distillation fraction P solid catalyst column strong heat petroleum fraction Q Fig. 8.1 (a) Fraction P and fraction Q contain different compounds. Describe two of the differences between the compounds in fraction P and those in fraction Q. 1. … … 2. … … [2] (b) Name process Y. … [1] (c) The rate of reaction in process Y is increased by using a powdered solid catalyst and a high temperature. (i) State why the catalyst is used in the form of a powder. … … [1] (ii) Explain how a high temperature increases the rate of reaction in process Y. Use ideas about particles in your answer. … … [2] (d) Bromine is added to two different samples of hydrocarbons A and B. Hydrocarbon A decolourises the bromine. Hydrocarbon B has no effect on the bromine. State these two types of hydrocarbon. A … B … [1] (e) The combustion of hydrocarbons produces a gas that turns limewater milky. (i) State the formula of this gas. … [1] (ii) Suggest one concern that people have as the proportion of this gas is increasing in the air. … … [1]

9 marks

Mark scheme: 8(a) (fraction P) lower boiling point ; smaller molecules ; weaker intermolecular (attractive) forces ; greater flammability ; lower viscosity ; max2 8(b) (catalytic or thermal) cracking ; 1 8(c)(i) increases surface area ; 1 8(c)(ii) particles move faster / have greater kinetic energy ; particles collide (with the catalyst) more often ; 2 8(d) (A) alkene / unsaturated and (B) alkane / saturated ; 1 8(e)(i) CO2 ; 1 8(e)(ii) reference to global warming / excessive (runaway / enhanced) greenhouse effect / negative effects such as climate change / polar melting / rising sea levels / ocean acidification ; 1

This question in 0653/42 Feb/March 2018

5 (a) Ethene is manufactured by cracking larger hydrocarbon molecules. (i) State what is meant by a hydrocarbon. … … [2] (ii) Complete the dot-and-cross diagram in Fig. 5.1 to show the bonding electrons in a molecule of ethene, C2H4. C C Fig. 5.1 [2] (iii) Describe a test to distinguish between ethane and ethene. State the result for each. test … ethane … ethene … [2] (b) During the complete combustion of hydrocarbons, carbon dioxide is formed. (i) The proportion of carbon dioxide in air is increasing. Explain why this gives cause for concern. … … [1] (ii) The combustion of hydrocarbons is an exothermic change. Explain what is meant by exothermic. Use ideas about energy transformations in your answer. … … … [2]

9 marks

Mark scheme: 5(a)(i) (compound / substance ) containing hydrogen and carbon (atoms) ; (carbon and hydrogen ) only ; 2 5(a)(ii) (circles not essential) four electrons shown between carbon atoms ; four H atoms drawn with single pair of electrons between each and a C atom ; 2 5(a)(iii) (test) (addition of) bromine ; (ethane) no change owtte and (ethene) decolourises ; 2 5(b)(i) global warming / any valid effect of global warming ; 1 5(b)(ii) thermal /heat energy released (by chemical reaction) / (chemical reaction causes) temperature increase ; chemical energy converted (to thermal / heat energy) ; 2

This question in 0653/41 May/June 2018

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

5 (a) Ethane, C2H6, is an alkane. (i) State the type of bonding between atoms in a molecule of ethane. … [1] (ii) Complete the structure of a molecule of ethane. H C [2] (b) Petroleum is separated into useful products by the process shown in Fig. 5.1. refinery gas gasoline gas oil petroleum Fig. 5.1 (i) Name this process. … [1] (ii) Compare the molecules in gasoline to the molecules in gas oil. Use ideas about boiling point ranges, molecular sizes and intermolecular attractive forces in your answer. … … … … … [3] (c) Ethene, C2H4, is an alkene. Name the process used to make ethene from fractions obtained from petroleum. … [1] (d) The atomic number of carbon is 6. State the electronic structure of a carbon atom. … [1]

9 marks

Mark scheme: 5(a)(i) covalent ; 1 5(a)(ii) C – C single bond ; six correctly located C-H single bonds ; 2 5(b)(i) fractional distillation ; 1 5(b)(ii) gasoline molecules • are smaller ; • have lower boiling points ; • have weaker intermolecular attractive forces ; 3 5(c) cracking ; 1 5(d) 2,4 ; 1

This question in 0653/42 Oct/Nov 2018

8 Fig. 8.1 shows the structures of three hydrocarbon molecules, A, B, and C. H H H H H H C C H C H H C C C H H H H H H H A B C Fig. 8.1 (a) (i) Name hydrocarbons A and B. A … B … [2] (ii) Describe the changes, if any, that are observed when bromine water is added separately to samples of hydrocarbons A and B. A … B … [2] (iii) Deduce the balanced equation for the complete combustion of hydrocarbon C. … + … … + … [2] (b) Hydrocarbon A is made in process Y, as shown in Fig. 8.2. fractional process Y distillation fraction P column mixture containing hydrocarbon A strong heat petroleum fraction Q Fig. 8.2 (i) Name process Y. … [1] (ii) Describe the difference in the boiling points of fraction P and fraction Q. Explain this difference in terms of the sizes of molecules and of intermolecular attractive forces. difference … explanation … … … [2]

9 marks

Mark scheme: 8(a)(i) (A) ethene ; (B) methane ; 2 8(a)(ii) (A) decolourises ; (B) no (visible) change ; 2 8(a)(iii) C3H8 + 5O2 → 3CO2 + 4H2O species ; balanced ; 2 8(b)(i) cracking ; 1 8(b)(ii) (difference) [(b.pt of) Q is greater] NOTE: no mark for difference, but must be correct for explanation marks to be awarded (explanation) Q has larger / heavier molecules ; molecules of Q have greater intermolecular attractive forces ; 2

This question in 0653/43 Oct/Nov 2018

2 (a) Fig. 2.1 shows the processes of fractional distillation and cracking. fraction L fractional distillation cracker column products of cracking hot fraction O petroleum Fig. 2.1 (i) State two ways in which fraction O differs from fraction L. 1. … … 2. … … [2] (ii) State one condition needed for the cracking process. … … [1] (b) Cracking breaks down large saturated hydrocarbon molecules into smaller hydrocarbon molecules. The equation below shows a chemical reaction that occurs during cracking. C18H38 C9H20 + 3C2H4 + CxHy Determine the values of x and y. x = … y = … [2] (c) Ethene, an alkene, has the formula C2H4. Complete the dot-and-cross diagram to show the bonding electrons in a molecule of ethene. C C [3] (d) The hydrocarbon C18H38 is an alkane. The alkanes are a homologous series. Explain what is meant by the term homologous series. … … … [2] [Total: 10]

10 marks

Mark scheme: 2(a)(i) fraction O molecules are larger / have more carbon atoms; fraction O has higher bp / is liquid not gas; fraction O is more viscous; fraction O molecules have stronger intermolecular attractive forces; fraction O is less flammable ; fraction O has higher density ; max 2 2(a)(ii) heat / high temperature / temp of 450 °C etc. or high pressure / 200 atm or catalyst; 1 2(b) x = 3; y = 6; 2 2(c) four hydrogen atoms used two attached to each carbon; two bonding pairs between carbon atoms; single bonding pair between each carbon and hydrogen; 3 2(d) (family of compounds with) the same general formula ; similar (chemical) properties ; 2

This question in 0653/42 Feb/March 2019

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 (a) A simple example of cracking is the cracking of ethane to produce ethene and hydrogen. C2H6 → C2H4 + H2 The energy level diagram for this reaction is shown in Fig. 2.1. energy C2H4 + H2 C2H6 reaction progress Fig. 2.1 (i) On Fig. 2.1 draw a double headed arrow ( ) to show the activation energy for this reaction. [1] (ii) Use the energy level diagram to explain why the reaction is endothermic. … … [1] (iii) State one condition required for the process of cracking. … [1] (b) Ethane and ethene are not in the same homologous series. Explain what is meant by the term homologous series. … … … [2] (c) Draw a dot-and-cross diagram to show the bonding in a molecule of ethane, C2H6. [3] (d) When fuels are burned, carbon dioxide is released into the atmosphere. State one possible negative effect of an increase in the concentration of carbon dioxide in the atmosphere. … … [1] (e) Complete the balanced symbol equation for the complete combustion of ethene, C2H4 , in oxygen. … C2H4 + … → … CO2 + [2] [Total: 11]

11 marks

Mark scheme: 2(a)(i) arrow from reactant energy level to the top of the curve ; 1 2(a)(ii) reactants have less chemical energy than products ; 1 2(a)(iii) high temperature / high pressure / catalyst ; 1 2(b) family of compounds with a general formula ; similar chemical properties ; 2 Question Answer Marks 2(c) six hydrogen atoms, three attached to each carbon ; one bonding pair between carbon atoms ; single bonding pairs between each carbon and hydrogen ; 3 2(d) global warming / enhanced greenhouse effect / climate change / named consequence of climate change ; 1 2(e) C2H4 + 3O2  2CO2 + 2H2O all formulae correct ; balanced (dependent on correct formulae) ; 2

This question in 0653/43 May/June 2019

8 (a) A bromine atom contains seven electrons in its outer shell. Complete the dot-and-cross diagram of a molecule of bromine in Fig. 8.1. Show only the outer shell electrons. Br Br Fig. 8.1 [2] (b) The boiling point of liquid bromine is 59 °C. Explain what happens to bromine molecules when liquid bromine boils. Use ideas about molecules and energy changes in your answer. … … … … [2] (c) Orange aqueous bromine is mixed with colourless aqueous potassium chloride. Predict the colour change, if any, in this reaction. Explain your answer. colour change … explanation … … [2] (d) When large hydrocarbon molecules are cracked, alkenes are produced. (i) State two conditions needed for this process. 1. … 2. … [2] (ii) Aqueous bromine is used to test for the presence of alkenes. State the colour change that indicates a positive result for this test. from … to … [1] (e) The formula of aluminium bromide is Al 2Br6. The melting point of aluminium bromide is 97 °C and the boiling point is 255 °C. Explain how this information suggests that aluminium bromide contains covalent bonds. Use ideas about attractive forces in your answer. … … … [2] [Total: 11]

11 marks

Mark scheme: 8(a) shared pair ; seven outer electrons in each bromine atom ; 8(b) distance between bromine molecules increases ; (because) energy is used to, break / overcome intermolecular forces ; 2 8(c) no colour change ; bromine is less reactive than chlorine / bromine does not displace chlorine ; 2 8(d)(i) high temperature ; catalyst ; 2 8(d)(ii) (from) orange (to) colourless ; 1 8(e) covalently bonded substances have (relatively) low melting points and boiling points / ionic compounds would have much higher melting points and boiling points ; attractive intermolecular forces are (relatively) low ; 2

This question in 0653/42 Feb/March 2020

2 (a) Cracking breaks down large saturated hydrocarbon molecules into smaller hydrocarbon molecules. (i) State what is meant when a hydrocarbon is described as saturated. … … [1] (ii) The equation for a cracking reaction is shown. C20H42 C10H22 + 3C2H4 + CxHy Determine the values of x and y. x = … y = … [2] (b) One of the products of cracking hydrocarbons is ethene, C2H4. (i) Draw a dot-and-cross diagram to show the bonding in a molecule of ethene. Show only the outer shell electrons. [2] (ii) State the colour change seen when ethene is added to aqueous bromine. from … to … [1] (c) The complete combustion of ethene is an exothermic reaction. (i) Identify the two compounds that are produced in this reaction. 1 … 2 … [2] (ii) State whether bond breaking and bond forming are endothermic or exothermic processes. Use your answer to explain why the combustion of ethene is an exothermic reaction. bond breaking is … bond forming is … explanation … … [2] [Total: 10]

10 marks

Mark scheme: 2(a)(i) (compound containing only carbon and hydrogen and) only single (covalent) bonds (between carbon atoms) ; 1 2(a)(ii) x = 4 ; y = 8 ; 2 2(b)(i) double bond between carbon atoms; all else correct including chemical symbols ; 2 2(b)(ii) orange to colourless ; 1 2(c)(i) carbon dioxide / CO2 ; water / H2O ; 2 2(c)(ii) (bond breaking is) endothermic AND (bond forming is) exothermic ; more energy released during bond formation than energy required for bond breaking ; 2

This question in 0653/42 Oct/Nov 2020

2 Compounds J, K and L are hydrocarbons. The structures of one molecule of compounds J, K and L are shown in Fig. 2.1. J K L Key: hydrogen carbon Fig. 2.1 (a) State which compound, J, K or L, is ethene. Explain your answer. compound … explanation … … … [1] (b) Ethene is made by cracking gas oil. (i) Describe what is meant by cracking. … … [1] (ii) State one condition required for cracking. … [1] (c) Draw a dot-and-cross diagram of the molecule of compound K. Show the outer shell electrons only. [2] (d) In the presence of a catalyst, one molecule of compound L reacts with one molecule of steam to produce carbon monoxide and hydrogen. Construct the balanced symbol equation for this reaction. … [2] (e) State two compounds that are produced during the complete combustion of compound K. 1 … 2 … [2] [Total: 9]

9 marks

Mark scheme: 2(a) (compound J) the molecule of J, has the formula C2H4 / is unsaturated ; 1 2(b)(i) breaking of large hydrocarbon molecules into smaller molecules ; 1 2(b)(ii) heat / use of a catalyst ; 1 2(c) 2 electrons shared in single bond between carbon atoms ; all else correct including the symbols ; 2 Question Answer Marks 2(d) CH4 + H2O → CO + 3H2 all formulae correct ; balanced ; 2 2(e) carbon dioxide ; water ; 2

This question in 0653/43 Oct/Nov 2020

8 The alkanes and the alkenes are both homologous series. Table 8.1 shows the formulae of some alkanes and alkenes. Table 8.1 number of carbon atoms formula of alkane formula of alkene 2 C2H6 C2H4 3 C3H8 C3H6 4 C4H10 10 C10H22 C10H20 15 (a) (i) Complete Table 8.1 by filling in the missing formulae. [2] (ii) All alkanes are hydrocarbons. State two other similarities between all alkanes. 1 … … 2 … … [2] (b) State the colour change seen when aqueous bromine is added to an alkene. from … to … [1] (c) Pentane, C5H12, can be cracked to form smaller molecules. Fig. 8.1 shows the structures and the formulae of pentane and some products of cracking pentane. H H H H H cracking H H H H H H C C C C C H C C C C C H + H H H H H H H H H C5H12 C5H10 + … H H H H H cracking H H H H C C C C C H H C C C H + H H H H H H H H C5H12 C3H8 + … Fig. 8.1 (i) Complete Fig. 8.1 to show the structures and the formulae of the missing products. [3] (ii) State two conditions needed for cracking. 1 … 2 … [2] [Total: 10]

10 marks

Mark scheme: 8(a)(i) C4H8 C15H32 C15H30 ;; all three correct = 2 one or two correct = 1 8(a)(ii) any two from: same general formula as each other ; similar chemical properties to each other ; all saturated / only single bonds ; 2 8(b) (from) orange (to) colourless ; 1 8(c)(i) H–H AND H2 ; ethene displayed formula ; C2H4 ; 3 Question Answer Marks 8(c)(ii) high temperature ; catalyst / high pressure ; 2

This question in 0653/42 May/June 2021

8 Fig. 8.1 shows the structures of ethane and ethene. H H H H H C C H C C H H H H ethane ethene Fig. 8.1 (a) (i) Ethane and ethene are hydrocarbons. State what is meant by the term hydrocarbon. … … [2] (ii) Use Fig. 8.1 to explain what is meant by the term unsaturated. … … [1] (b) The polymerisation of ethene forms the polymer poly(ethene). (i) Identify this type of polymerisation. … [1] (ii) Describe what happens to the ethene molecules during polymerisation. … … [1] (iii) Ethane cannot form a polymer. Explain why. … … [1] (c) Complete the balanced symbol equation for the complete combustion of ethene. C2H4 + … O2 … CO2 + … … [2] [Total: 8]

8 marks

Mark scheme: 8(a)(i) contain hydrogen and carbon ; only ; 2 8(a)(ii) unsaturated has (carbon to carbon) double bond ; 1 8(b)(i) addition ; 1 8(b)(ii) double bonds break (to form a polymer) ; 1 8(b)(iii) ethane does not have a double bond ; 1 8(c) C2H4 + 3 O2 → 2 CO2 + 2 H2O one mark for H2O ; balanced dependent on correct formulae ; 2

This question in 0653/43 May/June 2021

8 Heptane, C7H16, is a hydrocarbon. It is used to produce smaller molecules, as shown in Fig. 8.1. H H H H H H H H C C C C C C C H H H H H H H H C7H16 H H H H H H H C C + H C C C C C H H H H H H H H C2H4 C5H12 Fig. 8.1 (a) (i) State the name of this process. … [1] (ii) State two conditions needed for this process. 1 … 2 … [2] (b) Put ticks (3) in the boxes to show which statements describe each compound. Use Fig. 8.1 to help you. You may tick one or more box in each row. compound C7H16 C2H4 C5H12 It has molecules which contain 23 atoms. It is unsaturated. It is an alkane. It produces carbon dioxide and water when it burns. [3] (c) Describe the colour change when aqueous bromine reacts with C2H4. from … to … [1] (d) The compound C2H4 is a member of a homologous series. Describe two similarities that are shared by all members of a homologous series. 1 … 2 … [2] [Total: 9]

9 marks

Mark scheme: 8(a)(i) cracking ; 1 8(a)(ii) high temperature ; catalyst / high pressure ; 2 8(b) C7H16 C2H4 C5H12 It has molecules which contain 23 atoms.  It is unsaturated.  It is an alkane.   It produces carbon dioxide and water when it burns.    All correct (3 marks) 3 rows correct (2 marks) 2 rows correct (1 mark) 3 8(c) from orange to colourless ; 1 Question Answer Marks 8(d) (same) general formula ; similar chemical properties ; 2

This question in 0653/42 Feb/March 2022

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 structures of ethane and ethene are shown in Fig. 5.1. H H H H H C C H C C H H H H ethane ethene Fig. 5.1 (a) Put a tick (✓) in one box in each row of Table 5.1 to show which description is true for ethane only, which is true for ethene only and which is true for both ethane and ethene. Table 5.1 true for true for true for both ethane only ethene only ethane and ethene is a hydrocarbon is a saturated compound changes the colour of aqueous bromine [2] (b) State the number of bonding electrons between the two carbon atoms in ethene. Explain your answer. number of electrons … explanation … … [2] (c) A student investigates the combustion of ethane, as shown in Fig. 5.2. cobalt(II) burning limewater chloride ethane paper boiling tube 1 boiling tube 2 Fig. 5.2 The gases produced by the combustion of ethane pass through boiling tube 1 and boiling tube 2. (i) State the change in colour of the cobalt(II) chloride paper in boiling tube 1. Explain why this change happens. colour changes from … to … explanation … … [2] (ii) Explain what happens to the limewater in boiling tube 2. … … … [2] (d) Describe the formation of poly(ethene) from ethene. … … … … [2] [Total: 10]

10 marks

Mark scheme: 5(a) 2 true for true for true for both ethane only ethene only ethane and ethene is a hydrocarbon ✓ is a saturated ✓ compound changes the colour of ✓ aqueous bromine one correct ; all three correct ; 5(b) 4 ; 2 double bond / two bonds each, containing two electrons ; 5(c)(i) blue (to) pink ; 2 water (vapour) is made ; 5(c)(ii) limewater turns milky ; 2 because carbon dioxide is made ; 5(d) idea that, many (ethene) molecules join ; 2 correct reference to, monomer / (addition) polymerisation ;

This question in 0653/42 Oct/Nov 2022

8 The structures of the hydrocarbons propane and ethene are shown in Fig. 8.1. propane ethene H H H H H H C C C H C C H H H H H Fig. 8.1 (a) Name the homologous series which contains propane. … [1] (b) Describe how Fig. 8.1 shows that propane is saturated and that ethene is unsaturated. propane … … ethene . … … [2] (c) Ethene, C2H4, is used to make ethanol, C2H5OH. (i) Deduce the formula of the compound that reacts with ethene to make ethanol. … [1] (ii) Explain why ethanol is not considered to be a hydrocarbon. … … [1] (d) Complete the dot-and-cross diagram in Fig. 8.2 to show the bonding in a molecule of ethene. Show only the outer shell electrons. H H C C H H Fig. 8.2 [2] (e) Suggest a chemical test that can be used to distinguish between propane and ethene. State the observations for each. test … observations with propane … observations with ethene … [2] [Total: 9]

9 marks

Mark scheme: 8(a) alkane ; 1 8(b) propane contains only single bonds / propane has single bonds between C atoms ; 2 ethene has a double bond (between C atoms) ; 8(c)(i) H2O ; 1 8(c)(ii) contains oxygen ; 1 8(d) carbon-carbon double bond correct ; 2 carbon – hydrogen bonds correct ; e.g., 8(e) (aqueous) bromine (water) ; 2 propane – remains orange AND observations with ethene – goes (from orange to) colourless ;

This question in 0653/42 Feb/March 2023

5 Table 5.1 shows some information about alkanes and alkenes. Table 5.1 alkanes alkenes number of carbon atoms per molecule name formula name formula 1 methane CH4 does not exist 2 ethane ethene C2H4 3 propane C3H8 propene C3H6 4 butane C4H10 butene C4H8 8 octane C8H18 octene (a) The general formula of alkanes is CnH(2n+2). Deduce the general formula of alkenes. … [1] (b) Complete the table by filling in the formulae for ethane and for octene. [2] (c) Fig. 5.1 shows the structures of ethene and propene. ethene propene H H H H C C C C H H H CH3 Fig. 5.1 (i) Ethene and propene are unsaturated hydrocarbons. State what is meant by unsaturated and hydrocarbons. unsaturated … … hydrocarbons … … [2] (ii) Explain why methene does not exist. … … … [2] (d) Refinery gas, obtained from petroleum, contains both propane and butane. (i) State one use of refinery gas. … [1] (ii) Explain why propane and butane are in the same fraction. … [1] [Total: 9]

9 marks

Mark scheme: 5(a) CnH2n ; 1 5(b) C2H6 ; C8H16 ; 2 5(c)(i) (unsaturated because) they contain a (carbon-carbon) double bond ; (hydrocarbons) contain hydrogen and carbon only ; 2 5(c)(ii) (the idea that methene would contain) only one carbon atom / an alkene needs (at least) two carbon atoms ; the idea that a (C = C) double bond cannot form ; 2 5(d)(i) bottled gas / heating / cooking ; 1 5(d)(ii) similar boiling point ; 1

This question in 0653/41 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

8 Ethene, C2H4, is an alkene. Fig. 8.1 shows the structure of an ethene molecule. H H C C H H Fig. 8.1 (a) Naphtha is a fraction obtained from the distillation of petroleum. Naptha undergoes a process to produce ethene. (i) State the name of the process that produces ethene from naphtha. … [1] (ii) State two conditions needed for this process. 1 … 2 … [2] (b) Ethane, C2H6, is an alkane. (i) Give one similarity and two differences between a molecule of ethene and a molecule of ethane. similarity … … difference 1 … … difference 2 … … [3] (ii) The complete combustion of ethane, C2H6, forms two products. Write a balanced symbol equation for this reaction. … [2] (c) Ethene molecules react together to form poly(ethene). Part of the structure of poly(ethene) is shown in Fig. 8.2. 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 Fig. 8.2 State the number of ethene molecules used to form the part of the poly(ethene) structure shown in Fig. 8.2. … [1] [Total: 9]

9 marks

Mark scheme: 8(a)(i) cracking ; 1 8(a)(ii) any two from: high temperature ; high pressure ; catalyst ; 2 8(b)(i) similarity: both, have two carbon atoms / are hydrocarbons / contain carbon and hydrogen only / both are covalent / both are simple molecules ; differences (any two from): ethane has (two) more hydrogen atoms / 6 hydrogen not 4 ; ethene / alkene, has a (carbon to carbon) double bond and ethane / alkane, has only (carbon to carbon) single bonds ; ethene / alkene, is unsaturated and ethane / alkane, is saturated ; 3 Question Answer Marks 8(b)(ii) 2C2H6 + 7O2 → 4CO2 + 6H2O ; ; CO2 and H2O as products = (1) 2 8(c) five / 5 ; 1

This question in 0653/41 May/June 2024

8 The structures of ethene and ethane are shown in Fig. 8.1. H H H H C C H C C H H H H H ethene ethane Fig. 8.1 (a) Ethene is a member of the alkene homologous series. All alkenes are hydrocarbons with the same general formula. (i) State one other similarity between all members of the alkene homologous series. … … [1] (ii) State the general formula for alkenes and for alkanes. alkenes … alkanes … [2] (b) Many ethene monomer units react together in addition polymerisation to form poly(ethene). Draw the structure of a poly(ethene) molecule to show the part formed from three ethene monomer units. [2] (c) Cracking produces ethene from larger molecules. The cracking of molecule A forms a molecule of ethene and a molecule of compound B, as shown in Fig. 8.2. H H H H H H H C C C C C C H H H H H H H molecule A cracking H H C C + H H ethene compound B Fig. 8.2 (i) Complete Fig. 8.2 by drawing the structure of compound B. [2] (ii) State the conditions required for cracking. … and … [2] [Total: 9]

9 marks

Mark scheme: 8(a)(i) they all have similar chemical properties / all contain a (carbon-carbon) double bond ; 1 8(a)(ii) alkenes: CnH2n ; alkanes: CnH2n+2 ; 2 8(b) six carbon atoms bonded in a row (bonded with hydrogen atoms) ; 6 C and no double bonds and 12 H correctly bonded and continuation lines shown ; 2 Question Answer Marks 8(c)(i) 4 C atoms and 10 H atoms bonded in a row ; correct butane structure drawn to show single bonds ; 2 8(c)(ii) any two from: high temperature ; high pressure ; catalyst ; 2

This question in 0653/43 May/June 2024

8 (a) The formula for methanol is CH3OH. Complete the dot-and-cross diagram in Fig. 8.1 to show the bonding in methanol. Show outer-shell electrons only. H H C O H H Fig. 8.1 [3] (b) Ethene, C2H4, is an alkene. Ethane, C2H6, is an alkane. (i) State one difference in the bonding of ethene and of ethane. … … [1] (ii) The complete combustion reactions of both ethene and ethane produce carbon dioxide and water. Identify whether the statements are true or false. Tick (3) one box for each statement. true false One molecule of ethene produces the same number of molecules of carbon dioxide as one molecule of ethane. One molecule of ethene produces the same number of molecules of water as one molecule of ethane. The combustion reactions of ethene and ethane are both endothermic. [2] (c) The general formulae for alkenes and alkanes are shown in Table 8.1. Table 8.1 alkenes alkanes CnH2n CnH2n+2 Write the formula for: an alkene with 10 hydrogen atoms … an alkane with 10 hydrogen atoms. … [2] (d) Aqueous bromine is added to a sample of an alkene and to a separate sample of an alkane. State the colour of each sample after the aqueous bromine is added. alkene … alkane … [2] [Total: 10]

10 marks

Mark scheme: 8(a) 3 four pairs bonding electrons around carbon correct ; one bonding pair between oxygen and hydrogen (O-H bond) correct ; four non-bonding electrons on oxygen shell AND no extra electrons (on hydrogen) ; 8(b)(i) ethene, has a double bond / shares 4 electrons OR 1 ethane, has only single bonds / has single bond between carbons / shares 2 electrons ; 8(b)(ii) 2 two correct ; three correct ; 8(c) alkene C5H10 ; 2 alkane C4H10 ; 8(d) alkene no colour / colourless ; 2 alkane orange ;

This question in 0653/43 Oct/Nov 2024

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

5 (a) Table 5.1 shows properties of some halogens at room temperature (25 °C) and pressure. Table 5.1 melting point halogen state colour / °C fluorine –220 gas pale yellow pale chlorine –101 gas yellow‑green bromine liquid iodine +114 solid grey‑black astatine +302 black (i) State the colour of bromine at room temperature and pressure. … [1] (ii) Predict the: • melting point of bromine … • physical state of astatine at room temperature and pressure. … [2] (b) (i) State the type of chemical reaction when chlorine reacts with aqueous potassium bromide. … [1] (ii) Write the word equation for the reaction of chlorine with aqueous potassium bromide. … [1] (iii) Explain why chlorine does not react with aqueous potassium fluoride. … … [1] (c) Iodine reacts with iron to form iron(III) iodide, FeI3 . Complete the balanced symbol equation for this reaction. ……. FeI3 [1] (d) Aqueous bromine is used to distinguish between saturated and unsaturated hydrocarbons. (i) Circle the type of reaction when aqueous bromine reacts with an unsaturated hydrocarbon. addition combustion polymerisation sedimentation [1] (ii) State the colour change when aqueous bromine is added to an unsaturated hydrocarbon. ……………………………………………… to ……………………………………………… [1] [Total: 9]

9 marks

Mark scheme: 5(a)(i) red-brown ; 1 5(a)(ii) melting point: from −100 to +24 (°C) inclusive ; 2 physical state: solid ; 5(b)(i) displacement ; 1 5(b)(ii) chlorine + potassium bromide → potassium chloride + bromine ; 1 5(b)(iii) (chlorine is) less reactive than fluorine ; 1 5(c) 3I2 + 2Fe → 2FeI3 ; 1 5(d)(i) addition ; 1 5(d)(ii) orange / orange brown to colourless ; 1

This question in 0653/41 May/June 2025

6 Alkanes and alkenes are two different homologous series. (a) State two general characteristics of a homologous series. 1 … 2 … [2] (b) Alkenes are unsaturated compounds. State what is meant by unsaturated compound. … … [1] (c) Name the process used to manufacture alkenes from alkanes. … [1] (d) Ethene is an alkene. Poly(ethene) is a polymer made from ethene molecules. State the general name for the small molecules that join together to form a polymer. … [1] (e) Ethene reacts with steam to form ethanol. (i) State the type of catalyst used in this reaction. … [1] (ii) The structure of ethanol is shown in Fig. 6.1. H H H C C O H H H Fig. 6.1 Explain why ethanol is not a hydrocarbon. … [1] [Total: 7]

7 marks

Mark scheme: 6(a) any two from: 2 same general formula ; similar chemical properties ; trend in physical properties ; 6(b) a compound that contains a double carbon to carbon bond ; 1 6(c) cracking ; 1 6(d) monomer ; 1 6(e)(i) acid(ic) ; 1 6(e)(ii) contains oxygen / contains atoms other than carbon and hydrogen ; 1

This question in 0653/42 May/June 2025

6 (a) Ethene is an alkene. The structure of ethene, C2H4 , is shown in Fig. 6.1. H H C C H H Fig. 6.1 Table 6.1 shows the formula of each product and the reaction conditions when ethene undergoes addition reactions with different molecules. (i) Complete Table 6.1. Table 6.1 molecule formula of product reaction conditions Br2(aq) room temperature H2O(g) C2H5OH C2H6 [4] (ii) The symbol (g) is used in Table 6.1. State the meaning of this symbol. … [1] (b) Table 6.2 shows the formulas and boiling points of some alkenes. Table 6.2 boiling point formula / °C C3H6 –47 C4H8 –7 C5H10 30 (i) Deduce the formula of the alkene that contains 7 carbon atoms. … [1] (ii) The alkenes in Table 6.2 are members of the same homologous series. State two ways the information in Table 6.2 supports this statement. 1 … … 2 … … [2] (iii) State how the information in Table 6.2 shows that alkenes are hydrocarbons. … … [1] [Total: 9]

9 marks

Mark scheme: 6(a)(i) 4 molecule formula of product reaction conditions Br2(aq) C2H4Br2 / CH2BrCH2Br ; room temperature H2O(g) C2H5OH high temperature OR acid catalyst ; H2 ; C2H6 nickel catalyst ; 6(a)(ii) gas / gaseous ; 1 6(b)(i) C7H14 ; 1 6(b)(ii) same general formula / always has twice as many hydrogen atoms as carbon atoms / successive members differ by CH2 ; 2 boiling points increase (down the series) ORA ; 6(b)(iii) (they all) contain hydrogen / H and carbon / C only ; 1

This question in 0653/43 May/June 2025

6 Fig. 6.1 shows the structure of ethene. H H C C H H Fig. 6.1 (a) Tick (✓) all the statements that are true for ethene. It is part of the alkane homologous series. It is formed by cracking large alkanes. It reacts with hydrogen to form ethane. It is a polymer. It decolourises aqueous bromine. [3] (b) Complete the dot-and-cross diagram in Fig. 6.2 to show the bonding in an ethene molecule. Show only the outer-shell electrons. H H C C H H Fig. 6.2 [2] (c) Complete the sentences about a reaction of ethene. Ethene reacts with … to form ethanol. This is an … reaction. The reaction happens in the presence of an … catalyst. [3] [Total: 8]

8 marks

Mark scheme: 6(a) ticks for: 3 is formed by cracking large alkanes (box 2); reacts with hydrogen to form ethane (box 3); decolourises aqueous bromine (box 5) ; 6(b) bonding pair between each hydrogen and carbon and no extra electrons anywhere ; 2 two bonding pairs between the carbons ; 6(c) steam ; 3 addition ; acid ;

This question in 0653/41 Oct/Nov 2025

6 (a) Fig. 6.1 shows the structures of ethene and ethane. H H H H C C H C C H H H H H ethene ethane Fig. 6.1 (i) Organic compounds in the same homologous series as ethene have the general formula CnH2n. Deduce the general formula for the homologous series to which ethane belongs. … [1] (ii) Name the homologous series to which ethene belongs and to which ethane belongs. ethene … ethane … [1] (b) Complete the sentences about a reaction of ethene. Ethene reacts with … to form ethane. This reaction is an … reaction. The reaction happens in the presence of a … catalyst. [3] (c) Fig. 6.2 shows the structure of butane. H H H H H C C C C H H H H H Fig. 6.2 Butane and ethane are in the same homologous series. The boiling point of ethane is –88 °C. Predict the boiling point of butane. Give a reason for your answer. boiling point … °C reason … … [2] [Total: 7]

7 marks

Mark scheme: 6(a)(i) CnH2n+2 ; 1 6(a)(ii) (ethene) alkene and (ethane) alkane ; 1 6(b) hydrogen ; 3 addition ; nickel / Ni ; 6(c) boiling point any temperature higher than –88 °C ; 2 reason idea of, longer chain length / larger molecule ;

This question in 0653/42 Oct/Nov 2025

6 Pentene is an alkene that contains one double carbon–carbon bond. (a) Fig. 6.1 shows the structure of one form of pentene. H H H H C C C C C H H H H H H Fig. 6.1 (i) Use Fig. 6.1 to deduce the molecular formula of pentene. … [1] (ii) The double carbon–carbon bond in pentene can be in different positions. Complete Fig. 6.2 to show the structure of one other form of pentene. C C C C C Fig. 6.2 [1] (iii) Pentene is a member of a homologous series. State what is meant by a homologous series. … … … … [2] (iv) Draw lines to show which descriptions are true for pentene. One has been drawn for you. description is the main constituent of natural gas reacts with hydrogen in the presence of a nickel catalyst reacts with steam in the presence of pentene an acid catalyst is a saturated hydrocarbon decolourises aqueous bromine [2] (b) Pentene combusts in a limited supply of oxygen to form two air pollutants: carbon monoxide and carbon particulates. (i) Complete the balanced symbol equation by adding the missing state symbols. C5H10(g) + 4O2(g) 3CO( … ) + 2C( … ) + 5H2O(l) [1] (ii) Name this type of combustion reaction. … [1] (iii) State one adverse effect of carbon particulates on human health. … [1] [Total: 9]

9 marks

Mark scheme: 6(a)(i) C5H10 ; 1 6(a)(ii) 1 ; 6(a)(iii) any two from 2 (family of similar compounds with) similar chemical properties ; trend in physical properties ; same general formula ; 6(a)(iv) lines to: 2 reacts with hydrogen in the presence of a nickel catalyst ; reacts with steam in the presence of an acid catalyst ; 6(b)(i) (g) and (s) ; 1 6(b)(ii) incomplete ; 1 6(b)(iii) respiratory problems / named respiratory disorder / cancer ; 1

This question in 0653/43 Oct/Nov 2025