5070 w12 er.pdf
Cambridge General Certificate of Education Ordinary Level
5070 Chemistry November 2012
Principal Examiner Report for Teachers
The hydroxide ion does combine with hydrogen ions but not with hydrogen, thus option A is incorrect.
The strongest distractor in this question was B, Group III. Atoms in Group III lose three electrons when they
form ions and atoms in Group V gain three electrons when they form ions. Thus X in the ion X3- was a
member of Group V.
Calcium oxide is a basic oxide, silica is an acidic oxide, and the reaction is an acid-base reaction.
Carbon dioxide is responsible for global warming and not carbon monoxide. Thus option A was incorrect.
The structures of two compounds were given and were very different. Therefore alternative D, structural
formula, was incorrect. The two compounds each had the molecular formula C4H10 and therefore the same
composition by mass.