Question

I make threesaturated solutions of AgCl (Ksp= 1.8•10-10). The first is in pure water, the second is in 0.01 M KNO3, and the third is in 0.01 M NaCl. I measure the concentration of Ag+in each solution. Which has the highest Ag+concentration? Which has the lowestAg+ concentration? Please explain why there are differences in concentrations between the solution with the highest and lowest concentrations. I’m not asking for the actual concentration, so you don’t need to do any math.highest: _________________________________lowest: _________________________________why:

Answer 1

AgCl is sparingly soluble in water and thus its Ksp value is 1.8*10^-10

AgCl when kept in water make an equilibrium -

AgCl(s) <-> Ag+(aq) + Cl-(aq)

Due to low value of Ksp the ions formed have very low concentrations

If we can reduce any of the ions it will disturb the equilibrium and thus more ions will be produced and thus solubility of AgCl will increase.

By adding KNO3 we are adding NO3- ions into the water.

KNO3 -> K+ + NO3-

Ag+ and NO3- react to form AgNO3 and thus Ag+ concentration will decrease

Ag+ + NO3- -> AgNO3

Decreasing Ag+ will shift the equilibrium

AgCl(s) <-> Ag+(aq) + Cl-(aq)

to the right side and thus more AgCl will dissolve.

But if we add NaCl into AgCl solution due to presence of NaCl as Na+ and Cl- ions in the water

NaCl -> Na+ + Cl-

The Cl - concentration will increase and thus the equiilibrium

AgCl(s) <-> Ag+(aq) + Cl-(aq)

will shift to the left side to decrease the extra Cl- ions and thus solubility of AgCl will decrease as more AgCl will present as solid.

So, highest Ag+ concentration will be in KNO3 solution and lowest in NaCl solution.