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AQA A2 Chemistry Transition metals question

Zak Amin
Posts: 18
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Active Member
Joined: 3 years ago
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I thought the answer for the question attached was:

[Al(H2O)6]3+ + 3H2NCH2CH2NH2 --> [Al(H2NCH2CH2NH2)3]3+ + 6H2O

Is there a reason why you're not meant to use ligand substitution here? The question even mentions that H2NCH2CH2NH2 can act both as a base and ligand. Perhaps I am missing something important in the question?

Any help is much appreciated

Thank you

1 Reply
Posts: 733
Honorable Member
Joined: 4 years ago

Aluminium hexa aqua ion is acidic - so it will react with bases such as OH/NH3.


When it forms a precipitate (Al(OH)3) - the precipitate is amphoteric. 


It can still continue reacting with bases but this time it will only react with OH (strong bases) - and redissolve


Therefore, with NH3 and Amine ligands, it will only react until it forms a precipitate and wont react further.


However, Cu2+ CAN react further with excess NH3 and amine ligands.


look at the table below. hopefully it should help you memorise the reactions.


IMG 2032


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