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Topic: Why does Aluminium chloride give an acidic solution when dissolved in water?  (Read 23945 times)

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Offline Tangera

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Hello!

My question is why does aluminium chloride give an acidic solution when dissolved in water? I am aware that AlCl3 is a covalent molecule that ionizes in water into Al3+ and Cl-...does this happen to have anything to do with it giving an acidic solution in water?? My guess is that H3O+ ions may be formed as well, but why then, will H3O+ ions give an acidic solution?

Thank you for helping!

Offline Borek

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What form does the Al3+ cation take in water?
« Last Edit: July 06, 2008, 01:35:17 PM by Borek »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline manyuen_wong

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Hello!

My question is why does aluminium chloride give an acidic solution when dissolved in water? I am aware that AlCl3 is a covalent molecule that ionizes in water into Al3+ and Cl-...does this happen to have anything to do with it giving an acidic solution in water?? My guess is that H3O+ ions may be formed as well, but why then, will H3O+ ions give an acidic solution?

Thank you for helping!

Al3+, having a high charge/surface area ratio charge density, polarizes the water ligands and ejects out H+ ions.
As a result of polarization by Al3+, there is a drift of electron density towards Al3+ and this weakens the OH bonds

Offline cliverlong

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Hello!

My question is why does aluminium chloride give an acidic solution when dissolved in water?

I am aware that AlCl3 is a covalent molecule that ionizes in water into Al3+ and Cl-
My textbook, Facer, A2 Chemistry and the following link

http://www.chemguide.co.uk/inorganic/period3/chlorides.html#top

states that anhydrous Aluminium Chloride is hydrolysed by water, through a few intermediates, ending up producing H3O+ and hence the acidity, not the simple ionisation that you have written.

Quote
I am aware that AlCl3 is a covalent molecule

again Chemguide gives more detailed information on the structure of Aluminium (III) Chloride and shows, depending on temperature, the dative bonds, not just covalent bonds, leading to a molecular formula Al2Cl6

Quote
I am aware that AlCl3 is a covalent molecule
Facer states that adding water to hydrated Aluminium Chloride , deprotonates the AlCl3 H2O complex producing H3O+ and hence the acidity.

Clive

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