CIE iGCSE Co-Ordinated Science C11.4 Alkanes Exam Style Questions Paper 3
Question
(a) (i) Complete the dot-and-cross diagram in Fig. 8.1 to show the bonding in a molecule of methane, CH4.
Show only the outer-shell electrons.
(ii) State the name of the type of chemical bonding present in a molecule of methane.
Explain your answer.
type of chemical bonding ……………………………………………..
explanation …………………………………………………………………….
(b) Complete the word equation for the complete combustion of methane.
methane + ……………………………………→ …………………………………… + …………………………………..
(c) (i) State the name of the pollutant gas produced during the incomplete combustion of methane.
(ii) State one adverse effect of the gas you have named in (c)(i) on the health of humans.
▶️Answer/Explanation
Ans : 8(a)(i) 1 shared pair of electrons ;
all else correct ;
8(a)(ii) covalent ;
bonding between 2 non-metals / shared electron pairs ;
8(b) oxygen ;
carbon dioxide and water ;
8(c)(i) carbon monoxide ;
8(c)(ii) poisonous ;
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 ;