I am not sure how to answer the question below

Question

What is the minimum mass of Na2CO3 (molar mass = 105.990 g/mol) that must be added to 43.4 mL of a 1.0 × 10–4 M AgNO3 solution in order for precipitation to occur? The Ksp of Ag2CO3 is 8.6 × 10–12. Assume no volume change occurs upon addition of Na2CO3.

Answer 1

Ag₂CO₃(s) <==> 2Ag⁺(aq) + CO₃^2-(aq)

Ksp = [Ag⁺]²[CO₃^2-]

[Ag⁺] = 1.0x10^-4 M

8.6x10^-12 = (1.0x10^-4)²(CO₃^2-)

[CO₃^2-] = 8.6x10^-4 M

Since the volume used is 43.4 ml, which is equivalent to 0.0434 L, we find moles of CO₃^2- needed...

8.6x10^-4 mol/L x 0.0434L = 0.0198 moles CO₃^2- required

Mass of Na₂CO₃ = 0.0198 mol CO₃^2- x 1 mol Na₂CO₃/mol CO₃^2- x 106 g/mol = 2.10 g Na₂CO₃ needed