What is molarity of Zn+2 ion in saturated soln of ZnCO3 that contains 0.25M Na2CO3?

Question

What is molarity of Zn+2 ion in saturated soln of ZnCO3 that contains 0.25M Na2CO3?

Answer 1

Ksp = [Zn++] [CO3--] = 1.5x10^-11 (from CRC Handbook)

Let x = molar solubility, then

1.5x10^-11 = [x] [0.25+x]

Assume 0.25>>x, so ignore it in the right bracket:

1.5x10^-11 = [x] [0.25]

Solving, x = [Zn++] = 6.0x10^-11 M.