CIE iGCSE Co-Ordinated Science C11.5 Alkenes Exam Style Questions Paper 3
Question
(a) The proton numbers and nucleon numbers of carbon and hydrogen are shown in Table 11.1
i) State the number of neutrons in a carbon atom and the number of neutrons in a hydrogen atom.
(ii) State the number of electrons in a carbon atom.
(b) (i) State the difference between a saturated hydrocarbon and an unsaturated hydrocarbon.
(ii) Aqueous bromine is used to show the difference between a saturated hydrocarbon and an unsaturated hydrocarbon.
Describe the result of the test with a saturated hydrocarbon.
(c) Fig. 11.1 shows the apparatus used for the catalytic cracking of a saturated hydrocarbon.
(i) State the purpose of the catalyst in the cracking of a saturated hydrocarbon.
(ii) Cracking is an endothermic reaction.
State what is meant by an endothermic reaction.
(d) The complete combustion of hydrocarbons produces the greenhouse gas carbon dioxide.
(i) Name one other greenhouse gas.
(ii) Identify the gas in the air that reacts with hydrocarbons during combustion.
(iii) Carbon dioxide is one of the gases found in clean air.
State the name of the two gases found in clean air in the greatest proportions.
▶️Answer/Explanation
Ans : 11(a)(i) carbon = 6 ;
hydrogen = 0 ;
11(a)(ii) 6 ;
11(b)(i) unsaturated has a C=C double bond ;
11(b)(ii) aqueous bromine remains orange ;
11(c)(i) speed up the reaction ;
11(c)(ii) temperature decreases / thermal energy is absorbed (from the surroundings) ;
11(d)(i) methane ;
11(d)(ii) oxygen ;
11(d)(iii) oxygen ;
nitrogen ;
Question
(a) Fig. 8.1 shows the separation of petroleum into useful fractions.
Only two fractions are shown.
(i) Petroleum is a fossil fuel.
State the name of one other fossil fuel.
(ii) State the name of the process shown in Fig. 8.1.
(iii) State the name of one fraction not shown in Fig. 8.1.
(iv) State one use for each of the fractions shown in Fig. 8.1.
refinery gas ……………………………………………………………………………..
diesel oil …………………………………………………………………………………..
(b) Cracking is a process that produces small alkene molecules from larger alkane molecules.
Ethane is an alkane.
Ethene is an alkene.
Fig. 8.2 shows the structure of ethane, C2H6.
Draw the structure of ethene, C2H4.
(c) Ethene is used to make a polymer.
(i) State the name of the polymer that is made from ethene.
(ii) State the type of polymerisation reaction that makes this polymer from ethene.
▶️Answer/Explanation
Ans : 8(a)(i) coal / natural gas ;
8(a)(ii) fractional distillation ;
8(a)(iii) gasoline / naphtha / bitumen ;
8(a)(iv) (bottled gas for) heating and cooking ;
fuel for diesel engines ;
8(b) 
carbon carbon double bond ;
all else correct ;
8(c)(i) poly(ethene) ;
8(c)(ii) addition (polymerisation) ;
Question
(a) Petroleum is a fossil fuel.
State the name of one other fossil fuel. (Sub-topic – C11.3)
▶️Answer/Explanation
Coal / natural gas
(b) Petroleum is separated into useful fractions by fractional distillation.
State why fractional distillation is a physical change and not a chemical change. (Sub-topic – C6.1)
▶️Answer/Explanation
Change is reversible / no new products formed
(c) The fractions obtained from petroleum have different uses.
On Fig. 2.1, draw one line from each fraction to its use. One line has been drawn for you. (Sub-topic – C11.3)
| Fraction | Use |
|---|---|
| Bitumen | Road surfaces |
| Gas oil | Diesel engine fuel |
| Gasoline | Petrol engine fuel |
▶️Answer/Explanation
Bitumen – road surfaces; Gas oil – diesel engine fuel; Gasoline – petrol engine fuel
(d) Ethane and ethene are both found in petroleum. Ethane, \( C_2H_6 \), is an alkane. Ethene, \( C_2H_4 \), is an alkene. (Sub-topic – C11.5)
(i) Explain why ethene is described as being unsaturated.
▶️Answer/Explanation
Contains a carbon-carbon double bond
(ii) State the chemical test used to distinguish between an alkane and an alkene.
Describe the observation for an alkane and for an alkene.
▶️Answer/Explanation
Test: Aqueous bromine
Observation for alkane: No change / stays orange
Observation for alkene: Decolourises
(iii) State the total number of atoms in one molecule of ethene, \( C_2H_4 \).
▶️Answer/Explanation
Six
(iv) Complete Fig. 2.2 to show the structural formula of ethane, \( C_2H_6 \).
▶️Answer/Explanation
H
H-C-C-H
H
(v) Ethene molecules react together when heated to make a polymer.
State the name of the polymer made from ethene.
▶️Answer/Explanation
Polyethene / polythene
Question
Fig. 5.1 shows three hydrocarbon molecules, A, B and C.
(a) (i) Complete the dot-and-cross diagram of molecule C. Show the outer shell electrons only.
(ii) Molecule C is a greenhouse gas.
State the name of one other greenhouse gas.
…………………………………………………………………………………………………………………….
(b) The reaction between molecule A and oxygen is exothermic.
Describe what is meant by an exothermic reaction.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(c) State and explain which molecule A, B or C represents a molecule of ethane.
molecule …………………..
explanation …………………………………………………………………………………………………..
…………………………………………………………………………………………………………………….
(d) (i) State and explain which molecule A, B or C is unsaturated.
molecule …………………..
explanation …………………………………………………………………………………………………….
……………………………………………………………………………………………………………………..
(ii) An orange solution is used to test if a hydrocarbon molecule is unsaturated or saturated.
State the name of this orange solution.
…………………………………………………………………………………………………………………….
(iii) Describe what is observed when the solution in (ii) is reacted with an unsaturated hydrocarbon molecule.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 5(a)(i) 1 shared pair ;
all else correct ;
5(a)(ii) water vapour ; carbon dioxide ;
5(b) (thermal) energy released ;
5(c) B – no mark and
has formula C$_{2}$H$_{6}$ ;
5(d)(i) A – no mark and
has two carbons but only four hydrogens / has general formula C$_{n}$H$_{2n}$ ;
5(d)(ii) (aqueous) bromine ;
5(d)(iii) decolourises ;