# Can't seem to match the answer! help!

1. Apr 26, 2005

### laker_gurl3

What is the concentration of Sr(OH)2 in a solution with a pH of 11?

The answer is SUPPOSED to be 5.0 x 10^-4...buuut i keep getting 0.001..
i didnt think this would be a complicated question.. all i did was found the pOH to be 3..and found the concentration of OH, giving me .001
what am i doing wrong?:S

2. Apr 26, 2005

### Artermis

I'm not completely sure (I should be sure though! :P)

Equation is:

Sr(OH)2 + H2O <==> 2OH- + Sr((OH)O <---??

But anyways, the important thing is that there the hydroxide anion has a subscript of 2. You have to pay attention to the stoichiometric rations; therefore the molar ratio of the concentration of Sr(OH)2 to OH is 1:2.

Your 0.001 concentration of OH- present in solution is correct, but then you have to divide it to two to get the concentration of the Sr(OH)2.

$$0.001 \div 2 = 0.0005 or 5.0 \times 10^{-4}$$

-Art

Last edited: Apr 26, 2005