Question

A) Calculate the concentration of zinc (II) ions in a solution containing 0.20 M hexaammine zinc(II) ion and 0.0116 M ammonia at equilibrium. The Kf of [Zn(NH3)4]^2+ is 2.8*10^9.

B) Calculate the solubility of lead (II) sulfate in a 0.0034 M solution of sodium sulfate. The Ksp for lead(II) sulfate is 1.83*10^-8.

Answer 1

             Zn^2+ (aq) + 4NH3(aq) -----------> [Zn(NH3)4]^2+ (aq)

E            x                   0.0116                        0.2

           Kf   = [Zn(NH3)4]^2+/[Zn^2+][NH3]^4

          2.8*10^9   = 0.2/x*(0.0116)^4

            x              = 0.2/2.8*10^9*(0.0116)^4   = 4.6*10^-7 M

    [Zn^2+]    =    x   = 4.6*10^-7M

B.   Na2SO4 ----------------> 2Na^+ (aq) + So4^2-

       0.0034M                                            0.0034M

PbSO4(s) -------------> Pb^2+ (aq) + SO4^2- (aq)

                                        s                     s+0.0034

[SO4^2-]   = s+0.0034   = 0.0034M

Ksp   = [Pb^2+]SO4^2-]

1.83*10^-8   = s*(0.0034)

    s= = 1.83*10^-8/0.0034    = 5.4*10^-6 M

The solubility of PbSO4 is 5.4*10^-6 M