19. lonic compounds containing cyanide ion show the same solubility behavior in

Question

19. lonic compounds containing cyanide ion show the same solubility behavior in water as do ionic compounds containing halide ion. Consider the exothermic reaction: Cu(H2O)42.(aq) + 4CN (aq)% Cu(CN)42 (aq) + 4H20(1) a. If the system described by the equation above is initially at equilibrium, with [Cu(H2O)-o10 M and [CN] = 0.20 M, determine the direction of the shift in position of equilibrium (left, right, no shift, or cannot be determined) and justify your answer (be complete) for each of the following. Temperature remains constant, except where noted. i. Some solid copper (II) sulfate pentahydraté is added ii. Some solid potassium cyanide is added. ii. Some solid sodium carbonate decahydrate is added iv. Some solid potassium nitrate is added. V. Some liquid water is added vi. Some 0.20 M NaCN is added. vii. Some 0.10M Cu(NO3)2 is added. vii. Some 3.0M HNO, is added (do not try this at home!). b. Excluding vii above, for each of the changes shown in Part a, what effect (decrease, increase, no effect or cannot be determined) would there be on the value for the equilibrium constant for the reaction?

Explanation / Answer

a) i. The equilibrium shifts to the right side.

Explanation: When solid Cu(II) sulfate pentahydrate is added, the concentration of Cu(H2O)42+ increases, hence according to Le-Chaterlier's principle, the equilibrium shifts in a direction to decrease its concentration, i.e. to the right side.

ii. The equilibrium shifts to the right side.

Explanation: When solid KCN is added, the concentration of CN- increases, hence according to Le-Chaterlier's principle, the equilibrium shifts in a direction to decrease its concentration, i.e. to the right side.

iii. The equilibrium shifts to the left side.

Explanation: When solid Na2CO3.10H2O is added, the concentration of Cu(H2O)42+ decreases due to its reaction with carbonate ion, hence according to Le-Chaterlier's principle, the equilibrium shifts in a direction to increase its concentration, i.e. to the left side.

iv. The equilibrium shifts to the left side.

Explanation: When solid KNO3 is added, the concentration of CN- decreases due to its reaction with KNO3, hence according to Le-Chaterlier's principle, the equilibrium shifts in a direction to increase its concentration, i.e. to the left side.

v. There will be no shift in the equilibrium.

Explanation: Addition of water will just decrease the concentration of all the species at equilibrium, but no shift in the equilibrium.

vi. The equilibrium shifts to the right side.

Explanation: When 0.2 M NaCN is added, the concentration of CN- increases (twice), hence according to Le-Chaterlier's principle, the equilibrium shifts in a direction to decrease its concentration, i.e. to the right side.

vii. The equilibrium shifts to the right side.

Explanation: When 0.1 M Cu(NO3)2 is added, the concentration of Cu(H2O)42+ increases (twice), hence according to Le-Chaterlier's principle, the equilibrium shifts in a direction to decrease its concentration, i.e. to the right side.

viii. There will be no shift in the equilibrium.

Explanation: HNO3 reacts neither Cu(H2O)42+ nor with CN-, hence, the equilibrium will not get affected.

b. Case (i): If the equilibrium shifts to the right side, then the equilibrium constant increases.

Case (ii): If the equilibrium shifts to the left side, then the equilibrium constant decreases.

Case (iii): If there is no shift in the equilibrium, the equilibrium constant will not affect.

Accordingly, you can answer i-viii in part a.

All the very best !

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