What is the maximum mass, in g, of magnesium oxide that can be obtained from the reaction of oxygen with 2.4 g of magnesium?

A.     2.4

B.     3.0

C.     4.0

D.     5.6

C

Questions 4 and 5 both required candidates to carry out a calculation of the yield of a reaction, one in terms of mass the other in terms of volume. A significant number of candidates left these questions blank, perhaps indicating they were uncertain of the answer and then failed to return to them before the end of the examination. Only about half of the candidates answered these questions correctly and for both the discrimination index was high. This would indicate that many candidates taking the examination were unfamiliar with routine calculations.