When anhydrous aluminium chloride reacts with water, solution Y is formed that contains a complex aluminium ion, Z, and chloride ions - AQA - A-Level Chemistry - Question 7 - 2018 - Paper 1

The complex ion Z, represented as $[Al(H_2O)_6]^{3+}$, can donate a proton to water, forming:

$[Al(H_2O)_6]^{3+} + H_2O \rightleftharpoons [Al(H_2O)_5(OH)]^{2+} + H_3O^+$

Observation 1: Effervescence due to the release of carbon dioxide gas as sodium carbonate reacts with the aluminium ion.

Observation 2: The formation of a white precipitate as aluminum carbonate forms when aluminium ions react with carbonate ions.

The net ionic equation for the reaction can be represented as:

$[Al(H_2O)_6]^{3+} + 3CO_3^{2-} \rightarrow Al_2(CO_3)_3(s) + 6H_2O$

Observation 1: A thickening of the solution, indicative of a gel formation as aluminium hydroxide precipitates.

Observation 2: The solution may become less clear due to the formation of a colloidal suspension.

The equation for the reaction of aluminium species with potassium hydroxide can be represented as:

$[Al(H_2O)_6]^{3+} + 3OH^- \rightarrow [Al(OH)_3](s) + 6H_2O$