Syllabus Edition
First teaching 2023
First exams 2025
Define a Brønsted–Lowry acid.
Which species in the following reaction acts as a Brønsted-Lowry base.
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H2SO4 (aq) + H2O (l)
Which species in the following equation is acting as a Brønsted-Lowry acid.
CO32- (aq) + H+ (aq) HCO3- (aq)
Propanoic acid, CH3CH2CO2H is classed as a weak acid.
Write an equation to show the dissociation of propanoic acid.
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A pH curve can be drawn from the data recorded from the following procedure
Step 1 Placing a fixed volume of a HCl (aq) into a beaker
Step 2 Add KOH (aq) in known small portions from a burette and stir
Step 3 Use pH meter to record pH after every addition of alkali
Sketch a curve on the graph in Fig. 6.1 for a strong acid - strong base titration that could be drawn after this procedure is carried out.
A titration was performed between ethanoic acid, CH3CO2H (aq) and sodium hydroxide, NaOH (aq). Using the information in Table 6.1, suggest which indicator would be suitable for this titration.
Table 6.1
| Indicator | pH range |
| Pentamethoxy red | 1.2 - 3.2 |
| Naphthyl red | 3.7 - 5.0 |
| 4-nitrophenol | 5.6 - 7.0 |
| Cresol purple | 7.6 - 9.2 |
Apart from using an indicator or pH probe, describe one test that could be used to show that hydrochloric acid is a stronger acid than ethanoic acid of the same concentration.
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A student carried out some acid-base titrations using different reactants.
The indicators and their pH range are given in Table 1.1.
Table 1.1
| Indicator | pH range |
| methyl red | 4.2 - 6.3 |
| bromothymol blue | 6.0 - 7.6 |
| bromocresol green | 3.8 - 5.4 |
| phenolphthalein | 8.2 - 10.0 |
In the first titration, they titrated 10.0 cm3 of 0.200 mol dm-3 HCl against 0.200 mol dm-3 aqueous ammonia.
Using Table 1.1, explain why methyl red is a suitable indicator for the first titration but phenolphthalein is not.
In a second titration, the student titrated 25.0 cm3 of 0.200 mol dm-3 sodium hydroxide against 0.100 mol dm-3 ethanoic acid solution.
Sketch the graph that would be obtained for this titration.
Using Table 1.1, explain why phenolphthalein is a suitable indicator for the second titration but methyl orange is not.
Explain whether the other two indicators in Table 1.1 are suitable for use in either titration.
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Malonic acid is a weak dibasic carboxylic acid with the formula C3H4O4. Draw the displayed structure of malonic acid.
Suggest, with a reason, whether ethanoic acid or malonic acid has a higher pH.
Apart from testing the pH, suggest how equimolar solutions of malonic acid and ethanoic acid may be distinguished.
3 marks30.0 of 0.075 mol dm-3 CH3COOH with a pH of 2.93 was slowly added to a sample of 10.0 cm3 0.150 mol dm–3 KOH with a pH of 13.1. The pH was measured throughout the addition.
On the following axes, sketch how the pH will change during the addition of a total of 30.0 of 0.075 CH3COOH.
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This question is about Brønsted-Lowry acids and bases.
Give the meaning of the term Brønsted-Lowry base.
[1]
Explain the term weak acid.
[2]
A student titrated 0.10 mol dm-3 acid into a conical flask containing 25.0 cm3 of 0.1 mol dm-3 of a base, recording the pH with each addition of acid.
The student repeated the procedure using different combinations of acids and bases.
Identify which curve shown above in Fig. 5.1, is the acid-base combination for the following:
Identify which indicator given in Table 5.2 would be most suitable for curve Z. Justify your answer.
Table 5.2
| Indicator | pH range |
| Methyl orange | 3.1 - 4.4 |
| Phenolphthalein | 8.3 - 10.0 |
| Bromothymol blue | 6.0 - 7.6 |
Water is amphoteric and will react with nitric acid and ammonia.
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A and B are two solutions of the same concentrations that have pH values of 3 and 6 respectively.
The variation of conductivity and concentration of a strong and weak monoprotic acid are shown in Fig. 2.1.
Identify the strong and weak acid from the information given and justify your choices.
Fig. 2.1
For acid 1 and acid 2 in Fig. 2.1 in part (b) compare the volume of 0.2 mol dm-3 NaOH required to neutralise 20 cm3 of 0.1 mol dm-3 solutions of the acids.
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Glycolic acid, C2H4O3, is an organic acid sometimes used to remove limescale, CaCO3, from electric kettles and coffee machines.
Predict, with a reason, a difference in the reaction between the same concentration of sulfuric acid and glycolic acid with samples of calcium carbonate.
A solution of hydrochloric acid has a pH of 1 and a solution of carbonic acid has a pH of 5. Determine the ratio of hydrogen ion concentrations of hydrochloric acid to carbonic acid.
Outline two ways, apart from using pH, which could allow you to distinguish between two solutions of carbonic acid and hydrochloric acid that have the same concentration.
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