Groundwater near mining operations must be monitored to ensure that the cyanide
ID: 963939 • Letter: G
Question
Groundwater near mining operations must be monitored to ensure that the cyanide ion, CN^-, used to extract gold front ore does not enter the environment. Cyanide rapidly forms a stable complex with silver ion, Ag^+, to produce Ag(CN)_2^- with a beta_2 constant of 1.3 Times 10^21. The large formation constant makes Ag^+ useful as a titrant for cyanide ion. Which one of the following equilibrium reactions corresponds to the beta_2 constant for the complexation reaction described above? Ag^+ (aq) + 2CN^-(aq) Ag(CN)_2^- (aq) 2Ag^+ (aq) + 2CN^-(aq) 2Ag(CN)_2^-(aq) Ag(CN)_2^-(aq) Ag^+ (aq) + 2CN^-(aq) Ag(CN)_2^-(s) Ag^+ (aq) + 2CN^-(aq)Explanation / Answer
Answer a.
Beta is a cumulative constant, coresponding here to the first two steps of formation: beta 2 = K1xK2.
Only a and b are complex formation reactions, but b has wrong coefficients.
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