Question

Consider the following equilibrium:
CaCO3(s)<->Ca 2+(aq) + CO3 2-(aq)

Which of the following reagents, when added to the equilibrium system, would cause more CaCO3 to dissolve?

a)KNO3(s), can't be this, NO3 is soluble with all negative ions
b)CaCO3(s), adding more CaCO3 won't cause it to dissolve more
c)H2C2O4(s)
d)Na2CO3(s)

The answer is not d because it will make more CaCO3(s)? So the answer is c.

Answer 1

c is the correct answer. H2C2O4 is oxalic acid and although it is a weak acid (both k1 and k2 are small) it does increase the H^+ concn in the solution and that will dissolve more CaCO3 just as any acid will. Technically, KNO3 will make it more soluble also because it will increase the ionic strength of the solution; however, I doubt that you have talked about that yet and I wouldn't pick that over c anyway. But if you will take more chemistry, file that somewhere in the back of your brain and remember it down the road.

Answer 2

Thanks! I'll keep that in mind.