CAIE IGCSE Chemistry 7. Acids, bases & salts Question Bank

Practise acid, base and salt chemistry through indicator colours, pH evidence, neutralisation equations and common reactions.

Covered syllabus points

7.1 The characteristic properties of acids and bases 7.2 Oxides 7.3 Preparation of salts

[Maximum number: 5]

Sulfuric acid can be manufactured from the raw materials sulfur, air and water. The process can be divided into four stages.
stage 1 converting sulfur into sulfur dioxide
stage 2 converting sulfur dioxide into sulfur trioxide
stage 3 converting sulfur trioxide into oleum, $\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}$
stage 4 converting oleum into sulfuric acid
stage 1

(a)

Sulfuric acid reacts with a hydrocarbon called benzene to produce benzenesulfonic acid, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{3} \mathrm{H}$ . Benzenesulfonic acid is a strong acid which ionises to produce hydrogen ions, $\mathrm{H}^{+}$ , and benzenesulfonate ions, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{3}{ }^{-}$ .

[ 5 ]

(i)

What is meant by the term strong acid?

[ 1 ]

(ii)

Describe how to show that a $1 \mathrm{~mol} / \mathrm{dm}^{3}$ solution of benzenesulfonic acid is a strong acid.

[ 2 ]

(iii)

Write a chemical equation for the reaction between benzenesulfonic acid and sodium carbonate, $\mathrm{Na}_{2} \mathrm{CO}_{3}$ .

[ 2 ]

$\mathrm{Na}_{2} \mathrm{CO}_{3}+2 \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{3} \mathrm{H} \rightarrow 2 \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{3} \mathrm{Na}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}$

formula of $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{3} \mathrm{Na}$ all formulae correct and balancing correct

[Maximum number: 2]

Iron ore contains iron(III) oxide, $\mathrm{Fe}_{2} \mathrm{O}_{3}$ . A blast furnace is used to extract iron from $\mathrm{Fe}_{2} \mathrm{O}_{3}$ .
Equations for some of the reactions in the blast furnace are shown.

$equation $1 \mathrm{C}+\mathrm{O}_{2} \rightarrow \mathrm{CO}_{2}$$

$equation $2 \mathrm{CaCO}_{3} \rightarrow \mathrm{CaO}+\mathrm{CO}_{2}$$

$equation $3 \quad \mathrm{CaO}+\mathrm{SiO}_{2} \rightarrow \mathrm{CaSiO}_{3}$$

Explain why the reaction in equation 3 can be described as an acid-base reaction.

M1 CaO is basic

M2 $\mathrm{SiO}_{2}$ is acidic

[Maximum number: 6]

Sulfur is an important element.

(a)

Dilute sulfuric acid is used to make salts known as sulfates.

A method consisting of three steps is used to make zinc sulfate from zinc carbonate.
step 1 Add an excess of zinc carbonate to $20 \mathrm{~cm}^{3}$ of $0.4 \mathrm{~mol} / \mathrm{dm}^{3}$ dilute sulfuric acid until the reaction is complete.
step 2 Filter the mixture.
step 3 Heat the filtrate until a saturated solution forms and then allow it to crystallise.

[ 5 ]

(i)

State two observations which would show that the reaction is complete in step 1.

1

2

[ 2 ]

M1 No more fizzing;

M2 $\left(\mathrm{ZnCO}_{3}\right)$ stops dissolving or a (white) solid remains / is visible

(ii)

Why is it important to add an excess of zinc carbonate in step 1?

[ 1 ]

To use up all the acid / $\mathrm{H}^{+}$ ions

(iii)

Name another zinc compound which could be used to make zinc sulfate from dilute sulfuric acid using this method.

[ 1 ]

(iv)

Suggest why this method would not work to make barium sulfate from barium carbonate and dilute sulfuric acid.

[ 1 ]

(b)

In a titration, a student added $25.0 \mathrm{~cm}^{3}$ of $0.200 \mathrm{~mol} / \mathrm{dm}^{3}$ aqueous sodium hydroxide to a conical flask. The student then added a few drops of methyl orange to the solution in the conical flask.
Dilute sulfuric acid was then added from a burette to the conical flask. The volume of dilute sulfuric acid needed to neutralise the aqueous sodium hydroxide was $20.0 \mathrm{~cm}^{3}$ .

2 \mathrm{NaOH}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+2 \mathrm{H}_{2} \mathrm{O}

[ 1 ]

(i)

What was the colour of the methyl orange in the aqueous sodium hydroxide?

[ 1 ]

[Maximum number: 2]

Dilute hydrochloric acid reacts with sodium carbonate solution.

2 \mathrm{HCl}(\mathrm{aq})+\mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{aq}) \rightarrow 2 \mathrm{NaCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{CO}_{2}(\mathrm{~g})

$2\mathrm{HCl(aq)}+\mathrm{Na_2CO_3(aq)} ightarrow2\mathrm{NaCl(aq)}+\mathrm{H_2O(l)}+\mathrm{CO_2(g)}$

(a)

Explain why effervescence is seen during the reaction.

[ 1 ]

(b)

Dilute hydrochloric acid was titrated with sodium carbonate solution.
- $10.0 \mathrm{~cm}^{3}$ of $0.100 \mathrm{~mol} / \mathrm{dm}^{3}$ hydrochloric acid were placed in a conical flask.
- A few drops of methyl orange indicator were added to the dilute hydrochloric acid.
- The mixture was titrated with sodium carbonate solution.
- $16.2 \mathrm{~cm}^{3}$ of sodium carbonate solution were required to react completely with the acid.

[ 1 ]

(i)

What colour would the methyl orange indicator be in the hydrochloric acid?

[ 1 ]

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Covered syllabus points

7. Acids, bases and salts question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

7. Acids, bases and salts question 2

7. Acids, bases and salts question 3

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (iv)

Question (b)

Question (i)

7. Acids, bases and salts question 4

Question (a)

Question (b)

Question (i)