A level paper 3 mistakes

Question 1

Define relative isotopic mass.

Answer 1

The mass of an atom of an isotope.
Relative to 1/12th of the mass of a carbon-12 atom.

Question 2

How would you draw a diagram of the apparatus used for filtration under reduced pressure.

Answer 2

Conical flask with side arm labelled ‘to pump’
Buckner funnel with perforations.
Bung around the neck of the flask.
Flat filter paper over the perforations.

Question 3

describe the recrystallisation process to obtain a pure, dry sample of paracetamol.

Answer 3

Dissolve crystals in the minimum volume of hot solvent.
Filter hot and allow to cool.
Filter and wash with a small amount of cold solvent.
Dry crystals in a warm oven.

Question 4

Describe what happens to the melting temperature of paracetamol if it is not pure.

Answer 4

melting temperature is lower.
Melts over a range of temperatures.

Question 5

In an experiment where you add sodium carbonate to HCl.
Describe changes to the method to improve accuracy using a clock and graph plotting.

Answer 5

Measure temperature every 30 secs for 2.5 mins.
Add sodium carbonate
Stir and measure the temperature every 30 secs for another 5 mins.
Plot a graph of temperature against time.
Extrapolate the lines for the 2 sets of points and determine the maximum temperature change.