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CAIE A-Level Chemistry 7.2 Brønsted–Lowry Acids and Bases

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

7.2 Brønsted–Lowry theory of acids and bases 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.

7.2 Brønsted–Lowry theory of acids and bases question 2

[Maximum number: 2]

Hydrogen halides are compounds formed when halogens (Group 17 elements) react with hydrogen. The bond polarity of the hydrogen halides decreases from HF to HI.

Some relevant data are shown in the table.

Table for Question 7.2 Brønsted–Lowry theory of acids and bases question 2 — CAIE A-Level Chemistry AS

The equation for the preparation of hydrogen chloride using concentrated sulfuric acid is shown.

H2SO4+NaCl→NaHSO4+HCl\mathrm{H}_{2} \mathrm{SO}_{4}+\mathrm{NaCl} \rightarrow \mathrm{NaHSO}_{4}+\mathrm{HCl}

Use the Brønsted-Lowry theory of acids and bases to identify the base and its conjugate acid in this reaction. Explain your answer.

Brønsted-Lowry base (base-I) =
conjugate acid (acid-II) =

7.2 Brønsted–Lowry theory of acids and bases question 3

[Maximum number: 1]

Sulfides are compounds that contain sulfur but not oxygen.

Hydrogen sulfide gas, H2 S( g)\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g}), is slightly soluble in water. It acts as a weak acid in aqueous solution.

State the meaning of weak acid.

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