Chemistry AQA A Level| Updated with Real Based
Questions with Correct Answers| Graded A+ for a
perfect 100% score
(1) Outline how to carry out an acid-base titration. - Correct Answer
✅💯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.
,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). - Correct Answer ✅💯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? - Correct Answer ✅💯To see indicator
colour change better.
(1) Why does rinsing the flask with water not affect the end point? -
Correct Answer ✅💯Water does not react ---> doesn't affect number of
moles present.
(1) Why is a conical flask used? - Correct Answer ✅💯Can be swirled
without losing any solution.
,(1) Why is swirling necessary? - Correct Answer ✅💯To ensure that
solutions mix and so react completely.
(2) How can we limit heat loss for practicals measuring Enthalpies of
Neutralisation/Displacement?
What is the main source of apparatus error - how can this be reduced? -
Correct Answer ✅💯1. Lagging in polystyrene cup.
2. Add a lid to the polystyrene cup.
Main source of apparatus error = thermometer ---> can reduce this by
increasing the temperature change.
---> can increase temperature change by using a lower volume but higher
concentration of solution.
(2) How can we use a graph to calculate the temperature change (for
Neutralisation/Displacement experiments)? - Correct Answer ✅💯1. Plot a
graph of temperature (y) against time (x).
2. Before the addition of reagent to solution (0-4 mins):
- Join points for first 3 minutes with a straight line.
- Extrapolate (extend) line to 4th minute.
3. After addition of reagent to solution (4-12 mins):
- Draw a line of best fit through the points between the 5th and 12th
minutes and extrapolate (extend) this line to 4th minute.
=> Temperature change can be measured - distance between 2 lines.
Show it clearly on graph.
, (2) Outline how to carry out a practical to measure Enthalpies of
Combustion. - Correct Answer ✅💯1. Fuel is burnt and the energy
released is used to heat a set volume of water.
2. Fuel continues to burn until the temperature of water rises by a set
change (20C etc.).
3. Mass of fuel used then measured using a balance.
4. Calculation.
(2) Outline how to carry out a practical to measure Enthalpies of
Neutralisation/Displacement. - Correct Answer ✅💯1. Solution is
measured out and placed in a polystyrene cup.
2. Initial temperature of solution recorded for a few minutes before second
reagent is added (allows temperature to equilibrate).
3. Set, known quantity (mass/volume) of second reagent is added into the
solution at fourth time.
4. Temperature recorded every minute until some cooling observed.
NB=> Polystyrene cup used to reduce heat loss.
(2) What are the main errors in the experimental procedure when
measuring Enthalpies of Combustion?
How can we reduce heat loss? - Correct Answer ✅💯1. Heat loss to
surroundings (air/flask)
2. Incomplete combustion.
3. High temperature changes lead to evaporation of water.
Questions with Correct Answers| Graded A+ for a
perfect 100% score
(1) Outline how to carry out an acid-base titration. - Correct Answer
✅💯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.
,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). - Correct Answer ✅💯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? - Correct Answer ✅💯To see indicator
colour change better.
(1) Why does rinsing the flask with water not affect the end point? -
Correct Answer ✅💯Water does not react ---> doesn't affect number of
moles present.
(1) Why is a conical flask used? - Correct Answer ✅💯Can be swirled
without losing any solution.
,(1) Why is swirling necessary? - Correct Answer ✅💯To ensure that
solutions mix and so react completely.
(2) How can we limit heat loss for practicals measuring Enthalpies of
Neutralisation/Displacement?
What is the main source of apparatus error - how can this be reduced? -
Correct Answer ✅💯1. Lagging in polystyrene cup.
2. Add a lid to the polystyrene cup.
Main source of apparatus error = thermometer ---> can reduce this by
increasing the temperature change.
---> can increase temperature change by using a lower volume but higher
concentration of solution.
(2) How can we use a graph to calculate the temperature change (for
Neutralisation/Displacement experiments)? - Correct Answer ✅💯1. Plot a
graph of temperature (y) against time (x).
2. Before the addition of reagent to solution (0-4 mins):
- Join points for first 3 minutes with a straight line.
- Extrapolate (extend) line to 4th minute.
3. After addition of reagent to solution (4-12 mins):
- Draw a line of best fit through the points between the 5th and 12th
minutes and extrapolate (extend) this line to 4th minute.
=> Temperature change can be measured - distance between 2 lines.
Show it clearly on graph.
, (2) Outline how to carry out a practical to measure Enthalpies of
Combustion. - Correct Answer ✅💯1. Fuel is burnt and the energy
released is used to heat a set volume of water.
2. Fuel continues to burn until the temperature of water rises by a set
change (20C etc.).
3. Mass of fuel used then measured using a balance.
4. Calculation.
(2) Outline how to carry out a practical to measure Enthalpies of
Neutralisation/Displacement. - Correct Answer ✅💯1. Solution is
measured out and placed in a polystyrene cup.
2. Initial temperature of solution recorded for a few minutes before second
reagent is added (allows temperature to equilibrate).
3. Set, known quantity (mass/volume) of second reagent is added into the
solution at fourth time.
4. Temperature recorded every minute until some cooling observed.
NB=> Polystyrene cup used to reduce heat loss.
(2) What are the main errors in the experimental procedure when
measuring Enthalpies of Combustion?
How can we reduce heat loss? - Correct Answer ✅💯1. Heat loss to
surroundings (air/flask)
2. Incomplete combustion.
3. High temperature changes lead to evaporation of water.
