Question

Select all that apply. The molar solubility of AgCl in 6.5 × 10−3 M AgNO3 is 2.5 × 10−8 M. In deriving Ksp from these data, which of the following assumptions is (are) reasonable? Ksp is the same as solubility. The molar solubility of AgCl is the same in 6.5 × 10−8 M AgNO3 as in pure water. Solubility of AgCl is independent of the concentration of AgNO3. [Ag+] does not change significantly upon addition of AgCl to 6.5 × 10−3 M AgNO3. [Ag+] after the addition of AgCl to 6.5 × 10−3 M AgNO3 is the same as it would be in pure water.

Answer 1

Ksp is only a temperature dependent parameter. It will not depend upon the ionic strength.

AgCl dissociates into Ag+ & Cl- . But when the solution previously contains Ag+(from AgNO₃) then due to common ion effect the dissociation of AgCl gets decreased.According to the expression of Ksp:

Ksp= [Ag⁺] [Cl^{​​​​​-}]

Here, major amount of Ag+ comes from strong electrolyte AgNO_​​​3 and very little comes from sparingly soluble salt AgCl. But Cl- comes from AgCl only.

Now, as previously mentioned that, Ksp is constant at a particular temperature, so the multiplied value of concentration of Ag+ & Cl- be constant. So, as Ag+ concentration becomes high, consequently Cl- concentration will be low and that's why the solubility of AgCl decreases and it depends upon the concentration of AgNO₃.

So, it can be assumed that, Ag+ concentration rarely changes upon addition of AgCl where solution contain AgNO_​​​3 previously at very high concentration than the solubility of AgCl.