08 Acids and Bases, Set B To print: Ctrl + P, paper A4, margins Default.
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08

Acids and Bases

Set BExam practice
Name
Time 1 hour
Total 33 marks

Use a copy of the Periodic Table where you need one.

A

Multiple choice

5 marks
1

Some statements about acids are given below.
I  pH is a measure of the H+ concentration in a solution.
II  The strength of an acid depends on its concentration.
III  Universal Indicator turns orange when placed in a solution of any acid.
IV  When acids react with metals, hydrogen ions gain electrons.
Which statements about acids are correct?

AI and II only
BI and IV only
CI, II and III
DI, II and IV
Answer [1]

Source: 2024 SMSS Sec 3 End-of-Year P1 Q11

2

Which statements about strong and weak acids are always correct?
1  Strong acids ionise to a greater extent in water than weak acids.
2  Strong acids are more concentrated than weak acids.
3  Strong acids have a lower pH than weak acids.

A1 only
B1 and 3 only
C2 and 3 only
D1, 2 and 3
Answer [1]

Source: 2024 CHS Sec 3 End-of-Year Section A Q21

3

The reactions of four different oxides W, X, Y and Z with hydrochloric acid and sodium hydroxide solution are shown (✓ means there is a reaction and ✗ means there is no reaction). Which row shows the correct types of oxide?

oxidehydrochloric acidsodium hydroxide
W✓✗
X✓✓
Y✗✗
Z✗✓
WXYZ
Aacidicamphotericneutralbasic
Bamphotericacidicbasicneutral
Cbasicamphotericneutralacidic
Dneutralbasicamphotericacidic
Answer [1]

Source: SJI 2020 Year 3 End-of-Year P1 Q25

4

A farmer adds ammonium nitrate to the soil to increase its nitrogen content. He then adds calcium hydroxide to neutralise the excess acid in the soil. Why is this not a good idea?

ACalcium hydroxide will cause the soil to become excessively alkaline.
BCalcium hydroxide will react with ammonium nitrate to release ammonia gas.
CCalcium hydroxide will react with ammonium nitrate to form calcium nitrate.
DCalcium hydroxide will make ammonium nitrate insoluble in water.
Answer [1]

Source: SJI 2020 Year 3 End-of-Year P1 Q22

5

Rat poison needs to be insoluble in rainwater, but soluble in the low pH of stomach contents. Which is a suitable barium compound to use as rat poison?

Abarium carbonate
Bbarium chloride
Cbarium nitrate
Dbarium sulfate
Answer [1]

Source: 2023 HYSS Sec 3 End-of-Year P1 Q16

B

Structured questions

28 marks
6

Acids in our daily lives. The stomach secretes gastric juice, which contains hydrochloric acid. Barium compounds that react with gastric juice produce aqueous barium ions, which are highly poisonous.
pKa is a measure of the extent to which an acid ionises. The larger the pKa value, the less the molecules ionise in solution, and so the weaker the acid. Table 8.1 shows the pKa values of some acids, and the volume of carbon dioxide produced when 1 g of calcium carbonate reacts with each acid for 1 minute.

acidpKavolume of CO2 produced / cm3
ethanoic acid4.72.32
citric acid3.14.02
lactic acid3.93.62
carbonic acid6.30.95
(a)
A barium meal containing barium sulfate is often given to patients before an X-ray.
(i)
Use ideas about solubility to explain why a barium meal is not poisonous.
[1]
(ii)
Explain why barium carbonate must not be used in place of barium sulfate in a barium meal.
[2]
(b)
Describe a test and the result to confirm the identity of carbon dioxide gas.
[2]
(c)
(i)
Explain how the ionisation in a weak acid differs from the ionisation of a strong acid, such as dilute hydrochloric acid.
[2]
(ii)
Using (c)(i) and the passage, state whether the pH and the pKa of a solution of a strong acid and of a weak acid are high or low.
pHpKa
strong acidhigh / lowhigh / low
weak acidhigh / lowhigh / low
[2]
(d)
Using the passage and Table 8.1, suggest which acid is the weakest and explain your reasoning.
[3]
(e)
Suggest why carbon monoxide has no effect on litmus paper.
[1]

Source: 2023 XMS Sec 3 WA3 Q8, adapted

7

Oxalic acid, H2C2O4, and sulfuric acid, H2SO4, each have two hydrogen atoms per molecule that can form H+ ions.

(a)
A 0.45 g sample of oxalic acid is dissolved in water and made up to 25.0 cm3. Determine the amount of oxalic acid, in moles, in this solution.
[1]
(b)
Solutions of oxalic acid and sulfuric acid of the same concentration have pH values of 3.2 and 0.90. Why are the pH values different?
[2]
(c)
A student titrated 25.0 cm3 of three acids, each 0.40 mol/dm3, against aqueous sodium hydroxide. Hydrochloric acid and ethanoic acid each needed 16.70 cm3, and sulfuric acid needed 33.40 cm3. Explain the similarities and differences between these volumes.
[3]
(d)
Determine the amount of hydrogen ions, in moles, in 25.0 cm3 of the 0.40 mol/dm3 hydrochloric acid.
[1]
(e)
Predict the volume of the same sodium hydroxide needed to neutralise the oxalic acid solution in (a).
[1]

Source: 2026 NAS Prelim P2 Q10, adapted

8

One industrial use of ethanoic acid is to remove limescale (calcium carbonate) from steel pipes.

(a)
Write the equation for the reaction that occurs when ethanoic acid reacts with calcium carbonate.
[2]
(b)
Hydrochloric acid is a strong acid and ethanoic acid is a weak acid.
(i)
Describe a simple test to show which is the strong acid and which is the weak acid.
[2]
(ii)
Describe the differences between strong and weak acids.
[2]
(iii)
Explain why hydrochloric acid should not be used for removing limescale from steel pipes.
[1]

Source: 2024 BLSS Prelim P2 Q10(b) and (c)