CAIE A-Level Chemistry 7.2.3 Brønsted–Lowry Theory

Practise describing acids as proton donors and bases as proton acceptors in forward and reverse reactions.

Exam points

identify the acid by the H+ it donates and the base by the H+ it accepts in the stated direction
use lone pairs and proton transfer to justify why a species such as ZnO or NH3 acts as a base
reclassify each species when the reaction direction reverses rather than treating its role as fixed

[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 7.2.3—Brønsted–Lowry theory of acids and bases question 1 — CAIE A-Level Chemistry AS

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

\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) =

M1

base is $\mathrm{Cl}^{-}$ AND conjugate acid is HCl

OR

base is $\mathrm{HSO}_{4}{ }^{-}$ AND conjugate acid is $\mathrm{H}_{2} \mathrm{SO}_{4}$

M2

$\mathrm{Cl}^{-} / \mathrm{HSO}_{4}^{-} /$ base is a proton acceptor

OR

$\mathrm{HCl} / \mathrm{H}_{2} \mathrm{SO}_{4} /$ (conjugate) acid has one more $\mathrm{H}^{+}$

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7.2.3—Brønsted–Lowry theory of acids and bases question 1