pratcial 2 energetics

Question 1

Describe how you would carry out an experiment to determine the enthalpy of solution of anhydrous magnesium chloride.

Answer 1

Stage 1 Method

(1a) Measures water with named appropriate apparatus

(1b) Suitable volume/mass / volume/mass in range 10 – 200 cm3/g

(1c) Into insulated container / polystyrene cup (NOT just ‘lid’)

(1d) Add known mass of MgCl2(s)

(1e) Use of ‘before and after’ weighing method. NOT ‘added with washings’

Stage 2 Measurements (could mark from diagram)

(2a) Record initial temperature (min 2 measurements)

(2b) Record T at regular timed intervals for 5+ mins / until trend seen

(2c) Plot T vs time

Stage 3 Use of Results (3a and 3b could come from diagram)

(3a) Extrapolate lines to when solid added (to find initial and final T)

(3b) Tfinal – Tinitial = ΔT / idea of finding ΔT from graph at point of addition

(3c) q = mcΔT

(3d) amount = mass/Mr (0.80/95.3 = 8.39 × 10−3 mol)

(3e) ΔHsoln = –q/8.39 × 10−3 or in words