EDEXCEL A LEVEL CHEMISTRY PAPER 2
2026 COMPREHENSIVE STUDY GUIDE WITH
CORRECT ANSWERS
◉Core Practical 7 and 15. Answer: Look at PMT -- testing for
unknown substances.
https://pmt.physicsandmathstutor.com/download/Chemistry/A-
level/Notes/Edexcel/Practical-
Skills/CP%2007%20&%20CP%2015%20-
%20Analysis%20of%20unknown%20compounds.pdf
◉Core Practical 13a: Follow the rate of the iodine-propanone
reaction using a titrimetric method Answer: METHOD:
Mix 25 cm3 of 1 mol dm−3 aqueous propanone with 25 cm3 of 1
mol dm−3 sulfuric acid in a beaker.
Start the stop clock the moment you add 50 cm3 of 0.02 mol dm−3
iodine solution. Shake the beaker to mix well.
Using a pipette, withdraw a 10 cm3 sample of the mixture and
transfer it to a conical flask.
Stop the reaction by adding a spatula measure of sodium
hydrogencarbonate. Note the exact time at which the sodium
hydrogencarbonate is added.
, Titrate the remaining iodine present in the sample with 0.01 mol
dm−3 sodium thiosulfate(VI) solution, using starch indicator. Copy
the table from the analysis section to record your results.
Continue to withdraw 10 cm3 samples at suitable time intervals
(approximately every 3 minutes) and treat them similarly. Always
note the exact time at which the sodium hydrogencarbonate is
added. Plot a graph of concentration against time... volume sodium
thiosulfate added is proportional to volume of iodine.
ERRORS:
Inaccurate timing of the colour change. Blue/black to colourless.
Adding starch slightly increases the volume which affects
concentration. Propanone is an irritant and highly flammable, keep
away from naked flames. Sodium thiosulphate releases SO2 when it
reacts, so keep the room well ventilated.
◉Core Practical 13b: Use a clock reaction to determine a rate
equation Answer: METHOD:
Measure 10.0 cm3 of potassium iodide solution into a small beaker
standing on a white tile.
Add 5.0 cm3 of sodium thiosulfate solution to the potassium iodide
solution.
Add 10 drops of starch solution to the mixture in the small beaker.
Starch acts as the indicator and must be used in each experiment.
Measure out 10.0 cm3 of the sodium peroxodisulfate solution. Pour
this into the mixture prepared in steps 1 and 2. Start the stop clock.
2026 COMPREHENSIVE STUDY GUIDE WITH
CORRECT ANSWERS
◉Core Practical 7 and 15. Answer: Look at PMT -- testing for
unknown substances.
https://pmt.physicsandmathstutor.com/download/Chemistry/A-
level/Notes/Edexcel/Practical-
Skills/CP%2007%20&%20CP%2015%20-
%20Analysis%20of%20unknown%20compounds.pdf
◉Core Practical 13a: Follow the rate of the iodine-propanone
reaction using a titrimetric method Answer: METHOD:
Mix 25 cm3 of 1 mol dm−3 aqueous propanone with 25 cm3 of 1
mol dm−3 sulfuric acid in a beaker.
Start the stop clock the moment you add 50 cm3 of 0.02 mol dm−3
iodine solution. Shake the beaker to mix well.
Using a pipette, withdraw a 10 cm3 sample of the mixture and
transfer it to a conical flask.
Stop the reaction by adding a spatula measure of sodium
hydrogencarbonate. Note the exact time at which the sodium
hydrogencarbonate is added.
, Titrate the remaining iodine present in the sample with 0.01 mol
dm−3 sodium thiosulfate(VI) solution, using starch indicator. Copy
the table from the analysis section to record your results.
Continue to withdraw 10 cm3 samples at suitable time intervals
(approximately every 3 minutes) and treat them similarly. Always
note the exact time at which the sodium hydrogencarbonate is
added. Plot a graph of concentration against time... volume sodium
thiosulfate added is proportional to volume of iodine.
ERRORS:
Inaccurate timing of the colour change. Blue/black to colourless.
Adding starch slightly increases the volume which affects
concentration. Propanone is an irritant and highly flammable, keep
away from naked flames. Sodium thiosulphate releases SO2 when it
reacts, so keep the room well ventilated.
◉Core Practical 13b: Use a clock reaction to determine a rate
equation Answer: METHOD:
Measure 10.0 cm3 of potassium iodide solution into a small beaker
standing on a white tile.
Add 5.0 cm3 of sodium thiosulfate solution to the potassium iodide
solution.
Add 10 drops of starch solution to the mixture in the small beaker.
Starch acts as the indicator and must be used in each experiment.
Measure out 10.0 cm3 of the sodium peroxodisulfate solution. Pour
this into the mixture prepared in steps 1 and 2. Start the stop clock.
