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.
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