This question is about sodium halides - AQA - A-Level Chemistry - Question 9 - 2020 - Paper 1

Misty or steamy white fumes are observed due to the formation of hydrogen chloride gas.

The chemical equation for the reaction is:

$\text{NaCl (s) + H}_2\text{SO}_4 \text{ (l) } \rightarrow \text{NaHSO}_4 \text{ (aq) } + \text{HCl (g)}$

The chloride ions act as a base or proton acceptor in the reaction.

The equation for the redox reaction is:

$\text{2NaBr (s) + 2H}_2\text{SO}_4 (l) \rightarrow \text{Na}_2\text{SO}_4 (s) + \text{Br}_2 (g) + \text{H}_2\text{O} (l) + \text{SO}_2 (g)$

In this reaction, bromine changes its oxidation state from -1 in NaBr to 0 in Br$_2$, indicating oxidation. Simultaneously, sulfur changes its oxidation state from +6 in H$_2$SO$_4$ to +4 in SO$_2$, indicating reduction. This simultaneous oxidation and reduction confirms that it is a redox reaction.

A yellow or orange solution is observed due to the formation of bromine, which imparts color to the solution.

The ionic equation for the reaction is:

$\text{Cl}_2 (aq) + 2\text{Br}^- (aq) \rightarrow 2\text{Cl}^- (aq) + \text{Br}_2 (aq)$