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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: RobertT on January 21, 2010, 12:33:02 AM

Title: Amount in mol.
Post by: RobertT on January 21, 2010, 12:33:02 AM

I recently stumbled upon a question that I didn't really understand how to answer.

For a 0.20 M solution of potassium sulfate, K₂SO₄, calculate the amount, in mol, of:
a) Potassium ions, K⁺
b) Sulfate ions, SO₄^2-
c)Oxygen atoms

I first thought that you would need to do n=C x V but with no Volume given i was unsure of how to answer it
I did decide to convert 0.20M/0.20mol L^-1 into g L^-1 = 0.20M x 174gMol^-1 which gave a result of 34.86 g L^-1. This is where i am stuck, I don't know what do do from here =/ Any help is good.
Thanks again, appreciate all the effort.

Title: Re: Amount in mol.
Post by: Ligander on January 21, 2010, 01:40:18 AM

Take one litre of your solution,  then calculate how many potassium ions etc. you have in your beaker.

Title: Re: Amount in mol.
Post by: Borek on January 21, 2010, 03:01:38 AM

Without given volume there is no answer to the question. Do like Ligander suggests.

Title: Re: Amount in mol.
Post by: RobertT on January 21, 2010, 03:50:51 AM

Quote from: Ligander on January 21, 2010, 01:40:18 AM

Take one litre of your solution,  then calculate how many potassium ions etc. you have in your beaker.

Quote from: Borek on January 21, 2010, 03:01:38 AM

Without given volume there is no answer to the question. Do like Ligander suggests.

Ahh, okay, Thanks for the help guys. The solution's for a, b and c are 0.10mol, 0.0500mol and 0.0500mol respectively.

If you consider the volume to be 1 litre, then
a) 0.4 mol K+ ions
b) 0.20 mol SO4 2- ions
c) 0.8 mol O atoms

I think the Book made an error, currently using Heinemann: Chemistry 2. Thanks again for the help, I'll put it down as 1L and continue with the questions. Thanks again for the help.