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Author Topic: Al + NaOH --> Al(OH)4 not Al(OH)3?  (Read 48513 times)

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zeoblade

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Al + NaOH --> Al(OH)4 not Al(OH)3?
« on: February 26, 2010, 07:37:28 PM »

When reacting Al metal and NaOH(aq), I thought initially I would get the following reaction:
Al(s) + 3NaOH(aq) --> Al(OH)3(aq) + 3Na(s)

But I feel this is not correct and wondered if it should be:
2Al(s) + 2NaOH(aq) + 3H2O(l) --> 2Al(OH)4-(aq) + 2Na+(aq) + 3H2(g)

In explaining this reaction, how does hydrogen gas combine together to be evolved in this reaction?

Is there a possibility it could also be like this and why?
2Al(s) + 2NaOH(aq) + 2H2O(l)  2NaAlO2(s) + 3H2(g)
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Schrödinger

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Re: Al + NaOH --> Al(OH)4 not Al(OH)3?
« Reply #1 on: February 26, 2010, 10:12:43 PM »

But I feel this is not correct and wondered if it should be:
2Al(s) + 2NaOH(aq) + 3H2O(l) --> 2Al(OH)4-(aq) + 2Na+(aq) + 3H2(g)
Is the equation balanced?

Is there a possibility it could also be like this and why?
2Al(s) + 2NaOH(aq) + 2H2O(l)  2NaAlO2(s) + 3H2(g)
This one is correct. It is actually one of the commercial methods to produce H2 gas(pure), if I'm not wrong.
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Borek

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Re: Al + NaOH --> Al(OH)4 not Al(OH)3?
« Reply #2 on: February 26, 2010, 10:21:28 PM »

But I feel this is not correct and wondered if it should be:
2Al(s) + 2NaOH(aq) + 3H2O(l) --> 2Al(OH)4-(aq) + 2Na+(aq) + 3H2(g)
Is the equation balanced?

Is there a possibility it could also be like this and why?
2Al(s) + 2NaOH(aq) + 2H2O(l)  2NaAlO2(s) + 3H2(g)
This one is correct. It is actually one of the commercial methods to produce H2 gas(pure), if I'm not wrong.

Note: once balanced they both describe the same process, I would not call one "correct" and the other "incorrect".
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Schrödinger

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Re: Al + NaOH --> Al(OH)4 not Al(OH)3?
« Reply #3 on: February 26, 2010, 10:37:55 PM »

Note: once balanced they both describe the same process, I would not call one "correct" and the other "incorrect".
But what about the aluminium hydroxide idea? Is that correct?
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zeoblade

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Re: Al + NaOH --> Al(OH)4 not Al(OH)3?
« Reply #4 on: February 26, 2010, 10:38:48 PM »

Al(s) + 2NaOH(aq) + 2H2O(l) --> Al(OH)4-(aq) + 2Na+(aq) + H2(g)

Sorry it should be this

2Al(s) + 2NaOH(aq) + 2H2O(l) --> 2NaAlO2(s) + 3H2(g)

So both describing the same process, how are Al(OH)4-(aq) and 2NaAlO2(s) related?
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Borek

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Re: Al + NaOH --> Al(OH)4 not Al(OH)3?
« Reply #5 on: March 24, 2014, 04:24:02 AM »

So both describing the same process, how are Al(OH)4-(aq) and 2NaAlO2(s) related?

This is basically the same substance:

Na+ + Al(OH)4- :rarrow: NaAlO2 + 2H2O
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