Q. If H₂S gas is bubbled into 0.2 M NaCN solution which is 0.02 M in each [Cd(CN)₄]^2- and [Ag(CN)₂]^-.then which option will be correct if H₂S produces 1 x 10^-9 M sulphide ion in the solution
( Given K_sp Ag₂S = 1 x 10^-50 M³; K_sp CdS = 7.1 x 10^-28 M²
K_inst [Ag(CN)₂]^- = 1 x 10^-20M² K_inst [Cd(CN)₄]^2- = 7.8 x 10^-18 M⁴)

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Ag₂S precipitates first from the solution

CdS precipitates first from the solution

None of them precipitate under the given conditions

Ag₂S precipitates at a sulphide concentration of 1 x 10^-15 M

Solution:

From question

Similarly,

[S^2-] needed to precipitate [Ag⁺]

[S²^-] needed to precipitate [Cd²⁺]

Since [S²^-] needed to precipitate Cd²⁺ ion is smaller than that of Ag⁺ ion.

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