CAIE A-Level Chemistry AS 7.2 Br Nsted Lowry Theory of Acids and Bases Questions

Practise identifying proton donors and acceptors, conjugate pairs and acid–base behaviour in equations and solutions.

Exam points

identify the acid as the proton donor and the base as the proton acceptor in each reaction direction
pair species that differ by one H+ and label each conjugate acid–base pair correctly
use equations and solution evidence to distinguish strong or weak acid behaviour from concentration

Covered syllabus points

7.2.1—Names and formulas of the common acids 7.2.2—Names and formulas of the common alkalis 7.2.3—Brønsted–Lowry theory of acids and bases 7.2.4—Strong acids and strong bases as fully 7.2.5—Appreciate that, under standard conditions,7.2.6—The differences in behaviour between strong 7.2.7—Neutralisation reactions occur when H +(aq)7.2.8—Salts are formed in neutralisation reactions 7.2.9—Sketch the pH titration curves of titrations 7.2.10—Select suitable indicators for acid-alkali

[Maximum number: 1]

NO and $\mathrm{NO}_{2}$ react at $25^{\circ} \mathrm{C}$ to give $\mathrm{N}_{2} \mathrm{O}_{3}$ as shown in the equation.

\mathrm{NO}(\mathrm{~g})+\mathrm{NO}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{N}_{2} \mathrm{O}_{3}(\mathrm{~g}) \quad \Delta H=-7.2 \mathrm{~kJ} \mathrm{~mol}^{-1}

The reaction is reversible and reaches equilibrium in a closed system.

A student titrates nitric acid with a base to form a solution containing aqueous magnesium nitrate.

Identify a base that the student could use.

magnesium hydroxide / Mg(OH) ${ }_{2}$

[Maximum number: 1]

Diethylzinc, $\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{Zn}$ , is added to NaOH(aq). Two reactions occur.

reaction $1 \quad\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{Zn}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{ZnO}+2 \mathrm{C}_{2} \mathrm{H}_{6}$

reaction $2 \quad \mathrm{H}_{2} \mathrm{O}+\mathrm{ZnO}+2 \mathrm{OH}^{-} \rightarrow \mathrm{Zn}(\mathrm{OH})_{4}{ }^{2-}$

In these reactions, which compounds act as Brønsted-Lowry acids?

reaction 1

reaction 2

$\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{Zn}$

$\mathrm{H}_{2} \mathrm{O}$

ZnO

the reaction is not acid / base

ZnO

[Maximum number: 1]

Four solutions, each of concentration $0.1 \mathrm{~mol} \mathrm{dm}^{-3}$ , were tested with a pH meter. The results are shown.

Table for Question 3 — CAIE A-Level Chemistry AS

Which statements explain these results?
1 Acid 2 has a lower pH than acid 1 because it is more soluble.
2 Base 2 has a higher concentration of hydroxide ions in solution than base 1.
3 Acid 1 dissociates less than acid 2.

1, 2 and 3 are correct

1 and 2 only are correct

2 and 3 only are correct

1 only is correct

[Maximum number: 2]

Solid magnesium nitride, $\mathrm{Mg}_{3} \mathrm{~N}_{2}$ , is a crystalline solid.

Explain why the solution produced in the reaction in (c)(ii) has a pH greater than 7. Refer to the products of the reaction in your answer.

M1 due to $\mathrm{OH}^{-}(\mathrm{aq})$

M2 EITHER acid-base reaction of water by ammonia OR dissociation of (some) $\mathrm{Mg}(\mathrm{OH})_{2}$

[Maximum number: 1]

Which statement about acids and bases is always correct?

An acid with two H atoms per molecule will be stronger than an acid with one H atom per molecule.

A concentrated solution of a strong acid will have a lower pH than a dilute solution of a weak acid.

A concentrated solution of a strong base will have a lower pH than a dilute solution of a weak base.

A strong acid is more dissociated in solution than a strong base.

[Maximum number: 1]

Which mixture will react to form exactly one mole of water?

volume $2.00 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{H}_{2} \mathrm{SO}_{4} / \mathrm{cm}^{3}$

volume $1.00 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{NaOH} / \mathrm{cm}^{3}$

250

500

250

1000

500

1000

[Maximum number: 1]

Solutions X and Y both have a concentration of $0.10 \mathrm{~mol} \mathrm{dm}^{-3}$ . A fixed volume of solution X is added to a conical flask, and solution Y is added from a burette to the conical flask. A titration is performed.

The diagram shows the pH titration curve for the acid-base reaction between the solutions.

Figure for Question 7 — CAIE A-Level Chemistry AS

What are solutions X and Y ?

solution X

solution Y

ammonia

nitric acid

ammonia

ethanoic acid

potassium hydroxide

nitric acid

potassium hydroxide

ethanoic acid

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7