Question

What is the molar solubility of MgC O (K = 8.5 x 10-5) in a 0.020 M C O 2- solution

Can you explain how to do this problem step by step? And if you use an equation, which one did you use?

The answer is: 4.3 x 10^-5

Answer 1

Given ksp = 8.5 E-5

Lets show the dissociation

MgC2O4                --- >             Mg²⁺ (aq) + C2O4^2- (aq)

I                                                            0                     0.020  

C          -x (molar solubility)                 +x                    +x

E                                                          x                      0.020+x

Ksp = [Mg²⁺][C2O4^2-]   = x (0.020+x)

8.5E-5 = x (0.020+x)

8.5E-5 = 0.020x + x²

x² + 0.020 x - 8.5E-5 = 0

We solve this quadratic equation.

After solving quadratic equation, x = 0.0036 M

This is moalar solubility

Molar solubility = x = 0.0036 M

Molar solubility = 3.6 E-3 M