Question

Given:

Ksp AgCl = 1.8 x 10-10
Ksp AgBr = 3.3 x 10-13
Ksp Agl = 1.5 x 10-16
Solid AgNO3 is slowly added to a solution that is 0.0010M each in NaCl,
NaBr, and NaI. Calculate the [Ag+] required to initiate the precipitation of
each silver halide. (NaCl, NaBr, NaI, AgNO3 and NaNO3 are soluble
compounds that are completely dissociated in dilute aqueous solution).

Answer 1

     NaCl --------------> Na^+ (aq) + Cl^-(aq)

0.001M                                          0.001M

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

                                           s              s+ 0.001

   [Cl^-]   = 0.001                  [s<<<<0.001]

Ksp = [Ag^+][Cl^-]

1.8*10^-10         =s*0.001

     s                   = 1.8*10^-10/0.001   = 1.8*10^-7 M

[Ag^+]   = s     = 1.8*10^-7 M

2

    NaBr--------------> Na^+ (aq) + Br^-(aq)

0.001M                                          0.001M

   AgBr -----------------> Ag^+ (aq) + Br^- (aq)

                                           s              s+ 0.001

   [Br^-]   = 0.001                  [s<<<<0.001]

Ksp = [Ag^+][Br^-]

3.3*10^-13         =s*0.001

     s                   = 3.3*10^-13/0.001   = 3.3*10^-10 M

[Ag^+]   = s     = 3.3*10^-10 M

3. NaI--------------> Na^+ (aq) + I^-(aq)

0.001M                                          0.001M

   AgI -----------------> Ag^+ (aq) + I^- (aq)

                                           s              s+ 0.001

   [I^-]   = 0.001                  [s<<<<0.001]

Ksp = [Ag^+][I^-]

1.5*10^-16         =s*0.001

     s                   = 1.5*10^-16/0.001   = 1.5*10^-13 M

[Ag^+]   = s     = 1.5*10^-13 M