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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]

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 2

[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

Question 3

[Maximum number: 1]

Which statement about acids and bases is always correct?

A

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

B

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

C

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

D

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

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