I think I know what I'm doing but I'm confused.

 

Basically I've been given this;

 

K= [NH4+(aq)] X [OH-(aq)] / [NH3(aq)] X [H2O(l)]

 

I've been given the values;

 

K= 3.19x10^-7

 

NH3(aq)= 1.00x10^-2 mol dm^-3

 

H2O(l)= 55.4 mol dm^-3

 

So I need to find the concentration of OH-. I know I have to rearrange the equation BUT since I have already been given a value for K what do I do with the H2O value? I thought I had to move that over to the left. Do I add it to K or multiply it to K?! Or am I way off?!

 

Any handy pointers are greatly appreciated!

 

Cheers

 

Pete.

You seem to be including something you aren't supposed to. Remember only aqueous species are included in equilibrium quotients.

Rearrange it so the OH is on the left - then apply what you know about rearranging equations....