   Chapter 17.6, Problem 1.4ACP

Chapter
Section
Textbook Problem

Silver undergoes similar reactions as those shown for gold. Both metals react with cyanide ion in the presence of oxygen to form soluble complexes, and both are reduced by zinc. The reaction of Ag+ with cyanide ion may be viewed as two sequential steps:(1) A g + ( a q ) + C N − ( a q ) ⇄ A g C N ( s ) (2) AgCN(s) +  C N − ( a q )   ⇄ [Ag(CN) 2 ] − ( a q ) A g + ( a q ) + 2   C N − ( a q )   ⇄ [Ag(CN) 2 ] − ( a q )                                                                     K f  = 1 .3  × 10 21 a. Use the solubility product equilibrium constant (Appendix J) of AgCN(s) to determine the equilibrium constant for Step 1. b. Use the equilibrium constants from Step 1 and the overall reaction to determine the equilibrium constant for Step 2. c. Excess AgCN(s) is combined with 1.0 L of 0.0071 M CN− (aq) and allowed to equilibrate. Calculate the equilibrium concentrations of CN− and [Ag(CN)2]− using the equilibrium constant for Step 2. Assume no change in volume occurs.

a)

Interpretation Introduction

Interpretation:

The value of equilibrium constant K1 for the given step (1) reaction has to be calculated.

Concept introduction:

Some metal ions when present in an aqueous solution containing anions or neutral species called Lewis base or ligands having a tendency to donate electron pairs to metal ions then complex ion formation will take place. Complex ions are stable and thus formation of these increase the solubility of the salt containing the metal ions same as in complex ions.

Example of metal ions that form complex ions include Ag+,Cd2+,Fe2+,Zn2+,Ni2+ etc.

Example of Lewis bases includes,NH3,OH etc.

For any general complex ion formation reaction,

xM+yL[MxLy]

Kf can be given as

Kf=[MxLy][M]x[L]y

Explanation

The value of equilibrium constant K1 for the given reaction is calculated below.

Given:

Refer to the Appendix J for the value of Ksp.

The value of solubility product constant Ksp for AgCN is 6.0×1017.

Ag+(aq)+CN1(aq)K1AgCN(s) (1)

AgCN(s)KspAg+(aq)+CN1(aq)                                                                (2)

Equation (1) is reciprocal of equation (2)

(b)

Interpretation Introduction

Interpretation:

The value of equilibrium constant K2 for the given step (2) reaction has to be calculated.

Concept introduction:

Some metal ions when present in an aqueous solution containing anions or neutral species called Lewis base or ligands having a tendency to donate electron pairs to metal ions then complex ion formation will take place. Complex ions are stable and thus formation of these increase the solubility of the salt containing the metal ions same as in complex ions.

Example of metal ions that form complex ions include Ag+,Cd2+,Fe2+,Zn2+,Ni2+ etc.

Example of Lewis bases includes,NH3,OH etc.

For any general complex ion formation reaction,

xM+yL[MxLy]

Kf can be given as

Kf=[MxLy][M]x[L]y

(c)

Interpretation Introduction

Interpretation:

The equilibrium concentration of CN and [Ag(CN)2] has to be calculated using equilibrium constant for step (2).

Concept introduction:

Some metal ions when present in an aqueous solution containing anions or neutral species called Lewis base or ligands having a tendency to donate electron pairs to metal ions then complex ion formation will take place. Complex ions are stable and thus formation of these increase the solubility of the salt containing the metal ions same as in complex ions.

Example of metal ions that form complex ions include Ag+,Cd2+,Fe2+,Zn2+,Ni2+ etc.

Example of Lewis bases includes,NH3,OH etc.

For any general complex ion formation reaction,

xM+yL[MxLy]

Kf can be given as

Kf=[MxLy][M]x[L]y

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