C3 2017

Question 1

Suggest one reason why the enthalpy change for this reaction cannot be determined directly by calorimetry

Answer 1

It is soluble
DeltaT for solid is hard to measure

Question 2

Describe how you would carry out an experiment to determine the enthalpy of solution of anhydrous magnesium chloride
You should use about 0.8g of anhydrous magnesium chloride
Explain how your results could be used to calculate the enthalpy of solution

Answer 2

Measure 50cm3 water using measuring cyclinder
Measure empty container
Into insultaed container
Add known mass of MgCl2
Measure container after
Record initial temp
Record T at regular timed intervals for 5 mins
Plot T vs Time
Extrapolate lines to when solid added
Tfinal-Tinital =deltaT
q=mcat
amount = mass/mr
deltaH = q/n

Question 3

Suggest why an electric heater is used rather than a bunsen burner in this hydrolysis

Answer 3

Ethanol is flammable

Question 4

State why reflux is used in this hydrolysis

Answer 4

Dont want reactant vapour to escape

Question 5

Suggest why sodium benzoate is soluble in cold water but benzoic acid is insoluble in cold water

Answer 5

Benzene ring is non-polar

Question 6

After the solid benzoic acid has been filtered off, it can be purified
Describe the method that the student should use to purify the benzoic acid

Answer 6

Dissolve in minimum hot solvent
Filter
Cool to recrystalise
Filter under reduced pressure
Wash and dry

Question 7

Suggest why the yield is not 100%

Answer 7

Product not dried

Question 8

Conditions and products of catalytic cracking

Answer 8

SLight pressure
High temp
Mainly branched alkanes and aromatics