Edexcel IAL Chemistry 17.23 amphoteric hydroxides and ionic equations

Separate the reaction types: hydroxide formation is deprotonation, excess alkali shows amphoteric behaviour, and excess ammonia often gives ligand exchange.

Exam points

Recognise amphoteric hydroxides dissolving in both strong acid and strong alkali.
Write zinc or chromium hydroxide equations that form soluble hydroxo complexes.
Distinguish deprotonation from ligand exchange in NaOH and NH3 reactions.

[Maximum number: 2]

This question is about transition metals and their compounds.

Three reactions were carried out on a solution containing $\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ ions.

Figure for Question 17.23—Write ionic equations to show the meaning of amphoteric behaviour, deprotonation and ligand exchange in the reactions question 1 — Edexcel A-Level Chemistry A2

Complete the equation for Reaction 1. State symbols are not required.

\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}+\ldots \ldots \ldots \ldots \ldots \mathrm{NH}_{3} \rightarrow

correct formula of iron(III) hydroxide

(1)

- rest of equation correct, conditional on correct precipitate

(1)

Examples of equation:
$\begin{aligned} & {\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}+3 \mathrm{NH}_{3} \rightarrow \mathrm{Fe}(\mathrm{OH})_{3}+3 \mathrm{H}_{2} \mathrm{O}+3 \mathrm{NH}_{4}^{+}} & \begin{array}{l} \mathrm{Ir} {\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}+3 \mathrm{NH}_{3} \rightarrow \mathrm{Fe}(\mathrm{OH})_{3}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3}+3 \mathrm{NH}_{4}^{+}} \end{array} \end{aligned}$

Allow $\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3}(\mathrm{OH})_{3}$

Ignore state symbols, even if incorrect Ignore square brackets around iron(III) hydroxide formulae

(2)

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17.23—Write ionic equations to show the meaning of amphoteric behaviour, deprotonation and ligand exchange in the reactions question 1