Practical 2 FAQ

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) Measure water w measuring cylinder
(1b) About 50cm3
(1c) Into polystyrene cup
(1d) Add known mass of MgCl2(s)
(1e) Use of ‘before and after’ weighing method.

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

Question 2

To accurately measure use

Answer 2

Volumetric pipette
Measuring cylinder

Question 3

Types of calorimetry experiments

Answer 3

Combustion reactions
Adding solid to solution
Two solutions reacting

Question 4

Which volume to use with combustion reaction

Answer 4

Volume of water

Question 5

Which volume to use for 2 solutions reacting

Answer 5

Total volume when calculating mass
Use one moles- limiting moles

Question 6

Assumption made in calorimetry

Answer 6

Energy transferred to water from reacting chemicals= energy released/taken in by reaction

Question 7

Sources of error for combustion calorimetry

Answer 7

• Heat loss to surroundings
• Incomplete combustion of fuel

Question 8

Sources of error solution calorimetry

Answer 8

Heat loss to surroundings

Question 9

Improvements for combustion calorimetry

Answer 9

Add a lid
Insulate sides
Reduce distance between flame and beaker

Question 10

Improvements for solution calorimetry

Answer 10

Add a lid
Insulate calorimeter