1.1. A student carries out an experiment to determine the enthalpy of neutralisation for the reaction between hydrochloric acid and sodium hydroxide.

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

The student adds 25.0 cm³ of 2.00 mol dm^-3 hydrochloric acid to a polystyrene cup.

The student then adds 25.0 cm³ of 2.00 mol dm^-3 sodium hydroxide to the same cup.

The temperature of the mixture increases by 12.5 ^oC.

Calculate the enthalpy change, ΔH, for this reaction in kJ mol⁻¹.

Assume that the specific heat capacity of the solution, c = 4.18 J K⁻¹ g⁻¹ and that the density of the solution is 1.00 g cm⁻³.

Suggest one reason why your calculated value may be less exothermic than the true value.

1.2. The thermometer used in the experiment has an uncertainty of ±0.1 ^oC for each reading.

Calculate the percentage uncertainty in the temperature change measured.

1.3. The Data Book value for the enthalpy of neutralisation of a strong acid with a strong base is −57.1 kJ mol⁻¹.

Explain, with reference to the experimental method, why the value calculated in part (a) is less exothermic than the Data Book value.

1.4. State one other assumption made about the solution when calculating the enthalpy change in part (a), and justify this assumption.