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

1. Observation 1: Effervescence or bubbling occurs as carbon dioxide gas is released.

2. Observation 2: The formation of a white precipitate indicates the presence of aluminum carbonate.

Equation:

$$2[\text{Al}( ext{H}_2\text{O})_6]^{3+} + 3\text{Na}_2 ext{CO}_3 \rightarrow 2[\text{Al}_2(\text{CO}_3)_3] + 6\text{Na}^+ + 6\text{H}_2\text{O}$$

1. Observation 1: A white gel-like precipitate forms indicating the presence of aluminum hydroxide.

2. Observation 2: The solution may become colourless as excess hydroxide ions complex the aluminum species.

Equation 1:

$$[ ext{Al}( ext{H}_2 ext{O})_6]^{3+} + 3 ext{OH}^- \rightarrow [ ext{Al(OH)}_3] + 6 ext{H}_2 ext{O}$$

Equation 2:

$$[ ext{Al(OH)}_3] + ext{OH}^- \rightarrow [ ext{Al(OH)}_4]^-$$