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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

Question 7

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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 rea... show full transcript

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

Step 1

Give an equation for this reaction.

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Answer

The reaction of anhydrous aluminium chloride with water can be represented by the equation:

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

Step 2

0 7 . 2 Give an equation to show how the complex ion Z can act as a Brønsted–Lowry acid with water.

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Answer

The complex ion Z, which is assumed to be ([\text{Al(H}_2\text{O})_6]^{3+}), can act as a Brønsted–Lowry acid by donating a proton to water:

$\text{[Al(H}_2\text{O})_6]^{3+} + \text{H}_2\text{O} \rightarrow \text{[Al(H}_2\text{O})_5(\text{OH})]^{2+} + \text{H}_3\text{O}^+$

Step 3

0 7 . 3 Describe two observations you would make when an excess of sodium carbonate solution is added to solution Y. In your equation, include the formula of each complex aluminium species.

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Answer

Observation 1: Effervescence (bubbles) will be seen due to the release of carbon dioxide gas.
Observation 2: A white precipitate will form, indicating the formation of aluminium carbonate.

Equation:

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

Step 4

0 7 . 4 Aqueous potassium hydroxide is added, until in excess, to solution Y. Describe two observations you would make. For each observation, give an equation for the reaction that occurs. In your equations, include the formula of each complex aluminium species.

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Answer

Observation 1: A white precipitate (aluminium hydroxide) forms initially. Equation 1:
$\text{[Al(H}_2\text{O})_6]^{3+} + 3\text{OH}^- \rightarrow \text{[Al(OH)}_3]_{(s)} + 6\text{H}_2\text{O}$
Observation 2: On adding excess potassium hydroxide, the precipitate dissolves, forming a colourless solution. Equation 2:
$\text{[Al(OH)}_3]_{(s)} + OH^- \rightarrow \text{[Al(OH)}_4]^{-}$

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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.

0 7 . 2 Give an equation to show how the complex ion Z can act as a Brønsted–Lowry acid with water.

0 7 . 3 Describe two observations you would make when an excess of sodium carbonate solution is added to solution Y. In your equation, include the formula of each complex aluminium species.

0 7 . 4 Aqueous potassium hydroxide is added, until in excess, to solution Y. Describe two observations you would make. For each observation, give an equation for the reaction that occurs. In your equations, include the formula of each complex aluminium species.

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