We’re being asked to determine in which solvent AgCl would be least soluble in.
The common ion effect states that the solubility of a salt is lower in the presence of a common ion. This means if there is a higher concentration of a common ion present, the less soluble a compound will be. The dissociation of AgCl in water is as follows:
The chloride ion, Cl–, has a charge of –1. Silver then has a charge of +1:
AgCl(s) ⇌ Ag+(aq) + Cl–(aq)
Among the given choices, pure water and 0.020 M AgNO3 don't contain common ions so the solubility of AgCl is not lowered in those.
We’ll now determine which between the remaining solutions have higher Cl– concentration: a higher Cl– (common ion) concentration will lead to lower solubility of AgCl.
In which of the following aqueous solutions would you expect AgCl to have the lowest solubility? Choose one answer.
a. 0.020 M KCl
b. pure water
c. 0.015 M NaCl
d. 0.020 M BaCl2
e. 0.020 M AgNO3