Some reactions of the [Al(H2O)6]3+(aq) ion are shown. Colourless solution containing a complex ion A Na2EDTA(aq) [Al(H2O)6]3+(aq) Na2CO3(aq) B(s) White precipitate that reacts to form a colourless solution containing complex ion C NaOH(aq) 5.1 Give the formula of the white precipitate B. State one other observation when Na2CO3(aq) is added to a solution containing [Al(H2O)6]3+(aq) ions. Give an equation for this reaction. 5.2 Give the formula of the complex ion C. State one condition needed for the formation of C from [Al(H2O)6]3+(aq) and NaOH(aq). Give an equation for this reaction. 5.3 Deduce the formula of the complex ion A. 5.4 Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has a pH < 7. Equation: Explanation:

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Some reactions of the [Al(H2O)6]3+(aq) ion are shown - AQA - A-Level Chemistry - Question 5 - 2020 - Paper 1

Question 5

Some reactions of the [Al(H2O)6]3+(aq) ion are shown. Colourless solution containing a complex ion A Na2EDTA(aq) [Al(H2O)6]3+(aq) Na2CO3(aq) B(s) White prec... show full transcript

Worked Solution & Example Answer:Some reactions of the [Al(H2O)6]3+(aq) ion are shown - AQA - A-Level Chemistry - Question 5 - 2020 - Paper 1

Step 1

Give the formula of the white precipitate B.

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Answer

The formula of the white precipitate B is [Al(H2O)3(OH)3].

Observation: When Na2CO3(aq) is added, bubbles or effervescence may be observed.

Equation:

ightarrow Al(H_2O)_3(OH)_3(s) + 6H_2O + 3CO_2$$

Step 2

Give the formula of the complex ion C.

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Answer

The formula of the complex ion C is [Al(OH)4]−.

Condition: An excess of NaOH is required for the formation of C.

Equation:

ightarrow [Al(OH)_4]^{-} + 6H_2O$$

Step 3

Deduce the formula of the complex ion A.

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Answer

The formula of the complex ion A is [Al(H2O)6]3+.

Step 4

Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has a pH < 7.

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Answer

The [Al(H2O)6]3+ complex ion has a high charge density, which leads to the hydrolysis of water. This results in the release of H+ ions, causing the solution to be acidic.

Equation:

ightleftharpoons Al(H_2O)_5(OH)^{2+} + H^+$$

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Some reactions of the [Al(H2O)6]3+(aq) ion are shown - AQA - A-Level Chemistry - Question 5 - 2020 - Paper 1

Worked Solution & Example Answer:Some reactions of the [Al(H2O)6]3+(aq) ion are shown - AQA - A-Level Chemistry - Question 5 - 2020 - Paper 1

Give the formula of the white precipitate B.

Give the formula of the complex ion C.

Deduce the formula of the complex ion A.

Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has a pH < 7.

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