AQA A-Level Chemistry – Practice Exam with Questions and Answers – 100%
Solved
(1) Outline how to carry out an acid-base titration. - ✔✔✔-1. All apparatus rinsed with distilled
water and then with the relevant solution.
2. Using a pipette and pipette filler, pipette 25cm3 of NaOH into a conical flask. Touch surface of
solution with tip of pipette to ensure correct quantity is transferred.
3. Using a funnel, fill burette with acid and then remove funnel
- otherwise, some drops may fall through the titration after the initial reading has been taken =>
lower volume recorded than used.
4. Allow a small quantity of the acid to flow through the burette to ensure jet space is filled.
Note initial reading on burette.
- If jet space not filled, titre value higher than volume actually added.
5. Add 2-3 drops of phenolphthalein (or another suitable indicator) to the conical flask and
place it on a white tile - can see colour change better.
6. Add acid from burette into conical flask, swirling mixture during addition, until indicator
changes colour (pink ---> colourless).
7. During titration, rinse sides of conical flask with water ---> ensures all acid is in solution.
8. Note the burette reading.
9. Repeat experiment but add acid dropwise (drop by drop) towards the end point.
,AQA A-Level Chemistry – Practice Exam with Questions and Answers – 100%
Solved
10. Continue repeating until at least two concordant results obtained (within 0.10cm3).
(1) Outline how to prepare a Standard Solution in a Volumetric Flask (for an acid-base titration).
- ✔✔✔-1. All apparatus rinsed with distilled water.
2. Solute weighed out accurately, on a weighing boat, using a balance accurate to 2 dp.
3. Solid placed in beaker and dissolved in about 100cm3 of water.
4. Weighing boat rinsed with a small quantity of water and washings added to beaker - or,
weighing boat should be reweighed and the difference calculated.
5. Solution transferred to a 250cm3 volumetric flask.
6. Beaker rinsed with distilled water and washings added to volumetric flask.
7. Distilled water added to volumetric flask until made up to graduation mark - bottom of
meniscus should rest on the mark.
- If mark overshot, solution is more dilute than expected => start again.
8. Volumetric flask then inverted 20 times to ensure thorough mixing.
(1) Why do we use a white tile? - ✔✔✔-To see indicator colour change better.
, AQA A-Level Chemistry – Practice Exam with Questions and Answers – 100%
Solved
(1) Why does rinsing the flask with water not affect the end point? - ✔✔✔-Water does not
react ---> doesn't affect number of moles present.
(1) Why is a conical flask used? - ✔✔✔-Can be swirled without losing any solution.
(1) Why is swirling necessary? - ✔✔✔-To ensure that solutions mix and so react completely.
(10) During purification by recrystallisation, how do we know if a solvent is suitable? - ✔✔✔--
Impurities either need to be very soluble in solvent, as they then won't recrystallise with the
product.
or
- Insoluble in solvent as then they can be filtered and removed before cooling.
(10) Outline how to collect a liquid product. - ✔✔✔-Usually collected by distillation of the
reaction mixture:
1. Reaction mixture heated and the chemicals that boil at a range close to that of product are
collected.
2. Products boil off at different temperatures as they often have different intermolecular forces
than the reactants.
NB => Consider carefully whether products or reactants boil off first.
(10) Outline how to collect a SOLID product. - ✔✔✔-1. Solid collected by filtration from the
reaction mixture.
2. Solid then separated by filtration under reduced pressure using Buchner apparatus.
Solved
(1) Outline how to carry out an acid-base titration. - ✔✔✔-1. All apparatus rinsed with distilled
water and then with the relevant solution.
2. Using a pipette and pipette filler, pipette 25cm3 of NaOH into a conical flask. Touch surface of
solution with tip of pipette to ensure correct quantity is transferred.
3. Using a funnel, fill burette with acid and then remove funnel
- otherwise, some drops may fall through the titration after the initial reading has been taken =>
lower volume recorded than used.
4. Allow a small quantity of the acid to flow through the burette to ensure jet space is filled.
Note initial reading on burette.
- If jet space not filled, titre value higher than volume actually added.
5. Add 2-3 drops of phenolphthalein (or another suitable indicator) to the conical flask and
place it on a white tile - can see colour change better.
6. Add acid from burette into conical flask, swirling mixture during addition, until indicator
changes colour (pink ---> colourless).
7. During titration, rinse sides of conical flask with water ---> ensures all acid is in solution.
8. Note the burette reading.
9. Repeat experiment but add acid dropwise (drop by drop) towards the end point.
,AQA A-Level Chemistry – Practice Exam with Questions and Answers – 100%
Solved
10. Continue repeating until at least two concordant results obtained (within 0.10cm3).
(1) Outline how to prepare a Standard Solution in a Volumetric Flask (for an acid-base titration).
- ✔✔✔-1. All apparatus rinsed with distilled water.
2. Solute weighed out accurately, on a weighing boat, using a balance accurate to 2 dp.
3. Solid placed in beaker and dissolved in about 100cm3 of water.
4. Weighing boat rinsed with a small quantity of water and washings added to beaker - or,
weighing boat should be reweighed and the difference calculated.
5. Solution transferred to a 250cm3 volumetric flask.
6. Beaker rinsed with distilled water and washings added to volumetric flask.
7. Distilled water added to volumetric flask until made up to graduation mark - bottom of
meniscus should rest on the mark.
- If mark overshot, solution is more dilute than expected => start again.
8. Volumetric flask then inverted 20 times to ensure thorough mixing.
(1) Why do we use a white tile? - ✔✔✔-To see indicator colour change better.
, AQA A-Level Chemistry – Practice Exam with Questions and Answers – 100%
Solved
(1) Why does rinsing the flask with water not affect the end point? - ✔✔✔-Water does not
react ---> doesn't affect number of moles present.
(1) Why is a conical flask used? - ✔✔✔-Can be swirled without losing any solution.
(1) Why is swirling necessary? - ✔✔✔-To ensure that solutions mix and so react completely.
(10) During purification by recrystallisation, how do we know if a solvent is suitable? - ✔✔✔--
Impurities either need to be very soluble in solvent, as they then won't recrystallise with the
product.
or
- Insoluble in solvent as then they can be filtered and removed before cooling.
(10) Outline how to collect a liquid product. - ✔✔✔-Usually collected by distillation of the
reaction mixture:
1. Reaction mixture heated and the chemicals that boil at a range close to that of product are
collected.
2. Products boil off at different temperatures as they often have different intermolecular forces
than the reactants.
NB => Consider carefully whether products or reactants boil off first.
(10) Outline how to collect a SOLID product. - ✔✔✔-1. Solid collected by filtration from the
reaction mixture.
2. Solid then separated by filtration under reduced pressure using Buchner apparatus.
