1 A student is provided with hydrated copper(II) nitrate, Cu(NO3)2•3H2O.
The student needs to prepare a standard solution of Cu(NO3)2•3H2O with a concentration of 0.200 mol dm–3. The
student has access to usual laboratory apparatus and equipment.
Describe how the student would prepare 100.0 cm3 of this solution, giving quantities, apparatus and method.
[5]
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, 2 Oil of wintergreen is a liquid used in medicine to relieve muscle pain.
Compound H is a component in oil of wintergreen and can be synthesised from compound G, as shown below.
The boiling point and density of compound H are stated.
A student prepares a sample of compound H by the method below.
Step 1 Reflux 8.97 g of compound G for 30 minutes with an excess of methanol in the presence of a small
amount of sulfuric acid as a catalyst.
Step 2 Add an excess of aqueous sodium carbonate, Na2CO3(aq). Two layers are obtained.
Step 3 Purify the impure compound H that forms from the resulting mixture.
The student follows this method and obtains 5.32 g of pure compound H.
i. In Step 2, Na2CO3(aq) removes the sulfuric acid catalyst and any unreacted compound G from the mixture.
Write equations for this removal.
Removal of sulfuric acid
Removal of unreacted compound G
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, [3]
ii. Another student suggests that adding aqueous sodium hydroxide would be more effective in removing the
sulfuric acid catalyst than Na2CO3(aq).
Comment on whether the student's suggestion is an improvement for the preparation of compound H.
[1]
3(a) This question is about the reactions of acids.
What is the difference between a strong acid and a weak acid?
[1]
(b) Ethanoic acid, CH3COOH, is found in some descalers to soften hard water.
A student carries out a titration with a standard solution of sodium carbonate, Na2CO3, to determine the
percentage composition by mass of CH3COOH in a descaler.
The equation is shown below.
2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
i. The method is outlined below:
• Dissolve 6.50 g of the descaler in distilled water.
• Transfer the solution into a 250.0 cm3 volumetric flask.
• Make up to the mark with distilled water and invert several times.
• Pipette 25.0 cm3 of this solution into a conical flask and add a few drops of indicator.
• Titrate this solution with 0.200 mol dm–3 Na2CO3(aq), in the burette.
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, The student carries out a trial titration, followed by further titrations.
The results are shown in the table below.
The trial titration has been omitted.
Titration 1 2 3
3
Final reading/ cm 48.95 24.15 48.35
3
Initial reading/ cm 24.55 0.00 24.10
3
Titre / cm
Complete the table by adding the titres.
[1]
ii. Calculate the mean titre, to the nearest 0.05 cm3, that the student should use for analysing these results.
mean titre = ......................................... cm3 [1]
iii. Calculate the percentage composition by mass of CH3COOH in the descaler.
Assume that CH3COOH is the only acid in the descaler.
Give your answer to 3 significant figures.
percentage composition by mass = ......................................... % [5]
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The student needs to prepare a standard solution of Cu(NO3)2•3H2O with a concentration of 0.200 mol dm–3. The
student has access to usual laboratory apparatus and equipment.
Describe how the student would prepare 100.0 cm3 of this solution, giving quantities, apparatus and method.
[5]
© OCR 2025. You may photocopy this page. 1 of 80 Created in ExamBuilder
, 2 Oil of wintergreen is a liquid used in medicine to relieve muscle pain.
Compound H is a component in oil of wintergreen and can be synthesised from compound G, as shown below.
The boiling point and density of compound H are stated.
A student prepares a sample of compound H by the method below.
Step 1 Reflux 8.97 g of compound G for 30 minutes with an excess of methanol in the presence of a small
amount of sulfuric acid as a catalyst.
Step 2 Add an excess of aqueous sodium carbonate, Na2CO3(aq). Two layers are obtained.
Step 3 Purify the impure compound H that forms from the resulting mixture.
The student follows this method and obtains 5.32 g of pure compound H.
i. In Step 2, Na2CO3(aq) removes the sulfuric acid catalyst and any unreacted compound G from the mixture.
Write equations for this removal.
Removal of sulfuric acid
Removal of unreacted compound G
© OCR 2025. You may photocopy this page. 2 of 80 Created in ExamBuilder
, [3]
ii. Another student suggests that adding aqueous sodium hydroxide would be more effective in removing the
sulfuric acid catalyst than Na2CO3(aq).
Comment on whether the student's suggestion is an improvement for the preparation of compound H.
[1]
3(a) This question is about the reactions of acids.
What is the difference between a strong acid and a weak acid?
[1]
(b) Ethanoic acid, CH3COOH, is found in some descalers to soften hard water.
A student carries out a titration with a standard solution of sodium carbonate, Na2CO3, to determine the
percentage composition by mass of CH3COOH in a descaler.
The equation is shown below.
2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
i. The method is outlined below:
• Dissolve 6.50 g of the descaler in distilled water.
• Transfer the solution into a 250.0 cm3 volumetric flask.
• Make up to the mark with distilled water and invert several times.
• Pipette 25.0 cm3 of this solution into a conical flask and add a few drops of indicator.
• Titrate this solution with 0.200 mol dm–3 Na2CO3(aq), in the burette.
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, The student carries out a trial titration, followed by further titrations.
The results are shown in the table below.
The trial titration has been omitted.
Titration 1 2 3
3
Final reading/ cm 48.95 24.15 48.35
3
Initial reading/ cm 24.55 0.00 24.10
3
Titre / cm
Complete the table by adding the titres.
[1]
ii. Calculate the mean titre, to the nearest 0.05 cm3, that the student should use for analysing these results.
mean titre = ......................................... cm3 [1]
iii. Calculate the percentage composition by mass of CH3COOH in the descaler.
Assume that CH3COOH is the only acid in the descaler.
Give your answer to 3 significant figures.
percentage composition by mass = ......................................... % [5]
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