Chemistry- Selective Precipitation

[lananh]

Homework Statement

My molarity is wrong which keeps me from ding the rest of this problem...any help would be greatly appreciated.

A researcher has a 450.0 mL solution that is 0.421 M in Hg2(NO3)2 and 0.0191 M in Pb(NO3)2. She plans to add solid potassium iodide to separate the mixture by selective precipitation.

Ksp PbI2 = 1.4e-8
Ksp Hg2I2 = 1.2e-28

What is the maximum concentration of iodide ions that may be in solution to achieve the best separation possible?

M [I-]= ?

How many grams of potassium iodide should she add to achieve this?

g of KI

What will the percentage of mercury(I) ions remaining in solution be?

% Hg2+2

Homework Equations

ksp= ...

The Attempt at a Solution

hg2i2 = hg2 + 2i
1.2e-28 = [.421]^2
= 1.68e^-14, which is wrong and I have no idea what I am doing wrong

 

[Gokul43201]

Homework Equations

ksp= ...

Ksp=? Can you write down the expression for a general compound A_mB_n?

The Attempt at a Solution

hg2i2 = hg2 + 2i
1.2e-28 = [.421]^2

This calculation is not correct. First write down the correct expression for Ksp, then plug in numbers.

 

[lananh]

thanks, but I already figured that out
I failed to realize it said MAXIMUM
so would be ksp for pbi
= 8.6e-2
but now I am having problems with b and c