Question

Derive and thouroughly explain how the equilibrium constant Ksp for the silver chloride reaction can be determined using the concentrations of silver [Ag+] and chloride [Cl-]. Brief answers will be given no credit.

Answer 1

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

All the components are not completely soluble in water. Some of the solid reactants will be left undissolved in water.

We usually discuss the equilibrium phenomena at 25⁰ C.

At this temperature, we assume that there is an equilibrium established between the ion present in the solution and the undissolved solid reactant.

Now if we write the equilibrium constant for this equation then we get,

Kc= ([Ag⁺][Cl^-])/[AgCl]

But as we can see that the units of the concentration do not match as AgCl is in liquid form and its unit is grams /cm3.

Now we know that Kc is a constant so if we multiply it with AgCl still it will be a bigger constant.

Kc * [AgCl] = Ksp = [Ag⁺][Cl^-]

Here [Ag] and [Cl] both are in the aqueous form.  

So we get the value of Ksp using the concentrations of [Ag⁺] and  [Cl^-].