1.0 g of sodium hydroxide, NaOH, was added to 99.0 g of water. The temperature of the solution increased from 18.0 °C to 20.5 °C. The specific heat capacity of the solution is \({\text{4.18 J}}\,{{\text{g}}^{ - 1}}{{\text{K}}^{ - 1}}\). Which expression gives the heat evolved in \({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\)?

A.     \(\frac{{2{\text{.}}5 \times 100.0 \times 4.18 \times 1000}}{{40{\text{.}}0}}\)

B.     \(\frac{{2{\text{.}}5 \times 100.0 \times 4.18}}{{1000 \times 40{\text{.}}0}}\)

C.     \(\frac{{2{\text{.}}5 \times 100.0 \times 4.18 \times 40{\text{.}}0}}{{1000}}\)

D.     \(\frac{{2{\text{.}}5 \times 1{\text{.}}0 \times 4{\text{.}}18 \times 40{\text{.}}0}}{{1000}}\)

C

One respondent felt that this question was unnecessarily complicated. This was discussed at Grade Award and although there is some validity to this statement, it was considered that the question was fair but was considered one of the harder questions on the paper. With an associated difficulty index of 34.69%, the question was in fact the fifth hardest question overall.