4. Calculate the equilibrium concentration of Ag + (aq) in a solution that is in

Question

4. Calculate the equilibrium concentration of Ag+ (aq) in a solution that is initially 0.150 M AgNO3 and 0.500 M KCN. The formation constant for [Ag(CN)2]- (aq) is Kf= 1.0 x 1021

a. 8.9 x 10-21 M

b. 2.3 x 10 -21 M

c. 4.3 x 10 -22 M

d. 7.5 x 10 -22 M

e. 3.8 x 10 -21 M

5. If a solution of Pb(NO3)2 (aq) is mixed with a solution of NaBr(aq), what condition would cause precipitation of PbBr2 (s) to occur?

a. When [Na+][NO3-] < Ksp for PbBr2

b. When [Pb2+][Br -]2 < Ksp for PbBr2

c. When [Pb2+][Br -] < Ksp for PbBr2

d. When [Pb2+][Br -]2 > Ksp for PbBr2

e. When [Pb2+][Br - ] > Ksp for PbBr2

Explanation / Answer

Ag+ (aq) + 2CN- (aq) = [Ag(CN)2]- (aq)

FORMATION CONSTANT K =[ [Ag(CN)2]- (aq)] /[ Ag+ (aq) ] [CN- (aq)]2

                                    Ag+ (aq)    + 2CN- (aq)    =        [Ag(CN)2]- (aq)

INTIAL CONCENTRATION         0.150 M                 0.500 M                         0

LET AT EQUILIBRIUM               (.150-X)               (.500-2X)                         X

X M Ag+ (aq) REACTES

FORMATION CONSTANT K =[ [Ag(CN)2]- (aq)] /[ Ag+ (aq) ] [CN- (aq)]2

       K = X / (.150-X ) (.500-X )2

NOW SOLVE THE EQUATION TO GET X

5. d. When [Pb2+][Br -]2 > Ksp for PbBr2

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