A-Level AQA Chemistry Chemical Equilibria, Le Chateliers Principle & Kc: When anhydrous aluminium chlorid

Question

When anhydrous aluminium chloride reacts with water, solution Y is formed that contains a complex aluminium ion, Z, and chloride ions.

Give an equation for this reaction.

When aluminium chloride (	ext{AlCl}_3) reacts with water, the resulting complex aluminium ion Z can be represented as:

$$	ext{AlCl}_3 + 6	ext{H}_2	ext{O} ightarrow [	ext{Al}({	ext{H}}_2	ext{O})_6]^{3+} + 3	ext{Cl}^-$$

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Give an equation to show how the complex ion Z can act as a Brønsted–Lowry acid with water.

The equation showing the Brønsted–Lowry acid behavior of the complex ion Z in water can be written as:

$$[	ext{Al}({	ext{H}}_2	ext{O})_6]^{3+} + 	ext{H}_2	ext{O} ightarrow [	ext{Al}({	ext{H}}_2	ext{O})_5(	ext{OH})]^{2+} + 	ext{H}_3	ext{O}^+$$

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Describe two observations you would make when an excess of sodium carbonate solution is added to solution Y.

Observation 1: There would be effervescence (bubbles). This is due to the formation of carbon dioxide gas as the carbonate reacts with the acidic complex ion.

Observation 2: A white precipitate is formed. This indicates the formation of a solid complex species with sodium carbonate.

Give an equation for the reaction. In your equation, include the formula of each complex aluminium species.

The equation for the reaction with sodium carbonate can be represented as:

$$[	ext{Al}({	ext{H}}_2	ext{O})_6]^{3+} + 3	ext{Na}_2	ext{CO}_3 ightarrow [	ext{Al}_2(	ext{CO}_3)_3]^{3-} + 6	ext{H}_2	ext{O} + 6	ext{Na}^+$$

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Aqueous potassium hydroxide is added, until in excess, to solution Y.

Describe two observations you would make.

Observation 1: The solution turns to a colorless solution as the precipitate dissolves in excess OH- ions.

Observation 2: A white precipitate forms initially, which later dissolves with excess KOH.

For each observation give an equation for the reaction that occurs. In your equations, include the formula of each complex aluminium species.

Equation 1:
$$[	ext{Al}({	ext{H}}_2	ext{O})_6]^{3+} + 3	ext{OH}^- ightarrow [	ext{Al}({	ext{OH}})_3] + 3	ext{H}_2	ext{O}$$

Equation 2:
$$[	ext{Al}({	ext{OH}})_3] + 	ext{OH}^- ightarrow [	ext{Al(OH)}_4]^-$$

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

Worked Solution & Example Answer: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

Give an equation for this reaction.

Give an equation to show how the complex ion Z can act as a Brønsted–Lowry acid with water.

Describe two observations you would make when an excess of sodium carbonate solution is added to solution Y.

Give an equation for the reaction. In your equation, include the formula of each complex aluminium species.

Describe two observations you would make.

For each observation give an equation for the reaction that occurs.

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