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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.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

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 acids7.2.2—Names and formulas of the common alkalis7.2.3—Brønsted–Lowry theory of acids and bases7.2.4—Strong acids and strong bases as fully7.2.5—Appreciate that, under standard conditions,7.2.6—The differences in behaviour between strong7.2.7—Neutralisation reactions occur when H +(aq)7.2.8—Salts are formed in neutralisation reactions7.2.9—Sketch the pH titration curves of titrations7.2.10—Select suitable indicators for acid-alkali

Question 1

[Maximum number: 1]

NO and NO2\mathrm{NO}_{2} react at 25∘C25^{\circ} \mathrm{C} to give N2O3\mathrm{N}_{2} \mathrm{O}_{3} as shown in the equation.

NO( g)+NO2( g)⇌N2O3( g)ΔH=−7.2 kJ mol−1\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.

Question 2

[Maximum number: 1]

Diethylzinc, (C2H5)2Zn\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{Zn}, is added to NaOH(aq). Two reactions occur.

reaction 1(C2H5)2Zn+H2O→ZnO+2C2H61 \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 2H2O+ZnO+2OH−→Zn(OH)42−2 \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

(C2H5)2Zn\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{Zn}

H2O\mathrm{H}_{2} \mathrm{O}

H2O\mathrm{H}_{2} \mathrm{O}

H2O\mathrm{H}_{2} \mathrm{O}

H2O\mathrm{H}_{2} \mathrm{O}

ZnO

the reaction is not acid / base

ZnO

Question 3

[Maximum number: 1]

Four solutions, each of concentration 0.1 moldm−30.1 \mathrm{~mol} \mathrm{dm}^{-3}, were tested with a pH meter. The results are shown.

solution

formula of acid or base

pH

acid 1

CH3CO2H\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}

4

acid 2

HNO3\mathrm{HNO}_{3}

1

base 1

CH3NH2\mathrm{CH}_{3} \mathrm{NH}_{2}

11

base 2

NaOH

14

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.

A

1, 2 and 3 are correct

B

1 and 2 only are correct

C

2 and 3 only are correct

D

1 only is correct

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