When an organic acid, RCOOH, is neutralised by an alkali an exothermic reaction takes place. You will determine the enthalpy change of neutralisation, ΔH, for the following reaction. RCOOH(aq) + NaOH(aq) → RCOONa(aq) + H₂O(l) In this equation R is an alkyl group. FA 3 is a solution containing 120.1 g dm⁻³ of RCOOH. FA 4 is aqueous sodium hydroxide, NaOH.

1. (a)Method Experiment 1 • Support the cup in the 250 cm³ beaker. • Use the 25 cm³ measuring cylinder to transfer 25.0 cm³ of FA 3 into the cup. • Measure and record the temperature of this FA 3. Rinse the thermometer. • Place 25.0 cm³ of FA 4 into the 50 cm³ measuring cylinder. • Measure and record the temperature of the FA 4 in the measuring cylinder. Rinse the thermometer. • Tip the FA 4 from the measuring cylinder into the cup. Stir, then measure and record the highest temperature reached. • Calculate and record the average initial temperature of FA 3 and FA 4. • Calculate and record the difference between the average initial temperature and the highest temperature reached. • Rinse and dry the cup for use in Experiment 2. Experiment 2 • Repeat Experiment 1 using 50.0 cm³ of FA 3 and FA 4. You will need to use the 25 cm³ measuring cylinder twice to measure the FA 3. • Calculate and record the average initial temperature of FA 3 and FA 4. • Calculate and record the difference between the average initial temperature and the highest temperature reached. [4][4]
2. (b)(i)Calculations Calculate the energy released in Experiment 1. (Assume that 4.2 J of energy changes the temperature of 1.0 cm³ of solution by 1.0°C.) energy released = .............................................. J [1][1]
3. (b)(ii)Calculate the number of moles of RCOOH used in Experiment 1. Assume that the relative molecular mass, Mᵣ, of RCOOH is 122. Show your working. moles of RCOOH = .............................................. mol [2][2]
4. (b)(iii)Calculate the enthalpy change of neutralisation, ∆H, of RCOOH. Assume that the sodium hydroxide is in excess. enthalpy change of neutralisation of RCOOH = .......................... kJ mol⁻¹ sign value [1][1]
5. (c)Each measuring cylinder can be read to an accuracy of ± 0.5 cm³. Calculate the total maximum percentage error in the volumes of solution measured in each of Experiments 1 and 2. Experiment 1 total maximum percentage error = .............................................. % Experiment 2 total maximum percentage error = .............................................. % [2][2]
6. (d)A student repeated both experiments in (a) using hydrochloric acid in place of RCOOH. Suggest how the temperature rise when using HCl would compare to the temperature rise recorded in (a). Assume all volumes and concentrations of solutions, in mol dm⁻³, are the same. Explain your answer by considering the chemical bonds involved. [2][2]