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Topic: Stoichiometry Help  (Read 15181 times)

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Offline azncocoluver

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Stoichiometry Help
« on: August 10, 2011, 01:56:08 PM »
Aluminum sulfide reacts with water to form aluminum hydroxide and hydrogen sulfide.
(a) Write the balanced chemical equation for this reaction.
(b) How many grams of aluminum hydroxide are obtained from 10.5 g of aluminum sulfide?

So far, I have part of the balanced equation.. Al2S3 + H2O
I'm not sure how many molecules of water I need though.
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Offline Schrödinger

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Re: Stoichiometry Help
« Reply #1 on: August 10, 2011, 02:05:11 PM »
Quote from: azncocoluver on August 10, 2011, 01:56:08 PM
So far, I have part of the balanced equation.. Al2S3 + H2O
Start off by writing out the entire reaction, along with the products as well.
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Offline azncocoluver

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Re: Stoichiometry Help
« Reply #2 on: August 10, 2011, 02:28:29 PM »
Okay, so far I have..

Al2S3 + H2O  :rarrow: AlOH + H2S

I'm just confused about how many molecules I need.
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Offline fledarmus

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Re: Stoichiometry Help
« Reply #3 on: August 10, 2011, 02:33:24 PM »
What is the molecular formula for aluminum hydroxide?
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Offline azncocoluver

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Re: Stoichiometry Help
« Reply #4 on: August 10, 2011, 02:40:44 PM »
Oh yeah I forgot to balance the charges for aluminum hydroxide. So O2- and H1+, so hydroxide's charge would be 1-. Aluminum's charge is 3+ so aluminum hydroxide would be Al(OH)3?

If that's correct, my equation will now be:
Al2S3 + H2O  :rarrow: Al(OH)3 + H2S
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Offline fledarmus

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Re: Stoichiometry Help
« Reply #5 on: August 10, 2011, 02:45:32 PM »
Now you're getting there! You just need to finish balancing the equation now - get the same numbers of Al and S atoms on each side - and then you can figure out how much water you will need.
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Offline azncocoluver

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Re: Stoichiometry Help
« Reply #6 on: August 10, 2011, 02:57:01 PM »
Al2S3 + 6H2O  :rarrow: 2Al(OH)3 + 3H2S

I think that is correct, I just don't know if there is even a technique because what I did was guess and check. I think I got lucky because I just put a 2 in front of the reactant Aluminum hydroxide and that worked out well and then I figured I needed 6 Oxygen in the H2O product to equal the Oxygen in the aluminum hydroxide. Is there a technique or short cut or something to balance equations?
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Offline fledarmus

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Re: Stoichiometry Help
« Reply #7 on: August 10, 2011, 04:34:34 PM »
That's it  :D

I don't really know of any other technique, besides understanding what is actually happening on a mechanistic level and that is still some ways off. There are a few tricks, like concentrating first on the atoms that only appear in one place on each side of the arrow (unlike hydrogen in your example), but you'll pick those up as you do more of this type of problem.
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Offline azncocoluver

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Re: Stoichiometry Help
« Reply #8 on: August 10, 2011, 05:35:40 PM »
Thank you so much, I wish I had you as my teacher haha
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