Helping Son

Question

If AgNO3 solution is added to a solution containing Br- ions until the silver ion concentration is 8.17 x 10-5, what is the Br- ion concentration? The Ksp for AgBr is 5.2 x 10-13

Answer 1

Hi, Dana,

 

I'm sorry that this is late in coming, so I hope you have found an answer, or that this will help. 

 

To find the K_sp, generally, you'll balance the equation, then multiply the concentrations of the reactants, each raised to the power with the same value as their coefficients. 

 

For the general equation:

aA + bB --> [some product/s]

 

K_sp = [A]^a * [B]^b

I hope that looks familiar to your son.

 

So, for the specific problem given, you would set up your balanced equation like this:

Ag⁺ + Br^- <==> AgBr

 

Then, 

 

K_sp = [Ag⁺][Br^-]

 

Rearrange, algebraically, to isolate the unknown:

 

[Br^-] = K_sp/[Ag⁺]

 

For reference:

K_sp = 5.2 x 10^-13

[Ag⁺] = 8.17 x 10^-5

 

Plug the values in, and that should give you the answer.