A saturated copper (II) carbonate solution is created by mixing solid CuCO3 into

Q: A saturated copper (II) carbonate solution is created by mixing solid CuCO3 into

The correct answer is a). …solid mass decreases because NH3 consumes Cu2+ from solution, …favouring/producing partial or complete dissolution of CuCO3. About basicity of the solution: If NH3 is not in excess, Cu(OH)2 may precipitate. Thus the complex formation, not the basicity is the important fact.

ID: 962105 • Letter: A

Question

A saturated copper (II) carbonate solution is created by mixing solid CuCO3 into a beaker of water. No all of the CuCO3 dissolves, some reamins as a solid in the bottom of the beaker. What happens to the mass of solid in the bottom of the beaker when excess NH3 (Kb=1.8x10^-5) is added? The complex ion [Cu(NH3)4]2+ has a Kf value of 2.1x10^13.

a) solid mass decreases because NH3 consumes Cu2+ from solution

b) solid mass stays the same because [Cu(NH3)4]2+ replaces CuCO3

c) solid mass stays the same because NH3 is neutrally charged

d) solid mass increases because NH3 makes the solution more acidic

e) solid mass increases because Cu2+ can now form two different precipitates

f) solid mass decreases because NH3 makes the solution more basic

Explanation / Answer

The correct answer is a).

…solid mass decreases because NH3 consumes Cu2+ from solution, …favouring/producing partial or complete dissolution of CuCO3.

About basicity of the solution: If NH3 is not in excess, Cu(OH)2 may precipitate. Thus the complex formation, not the basicity is the important fact.

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A saturated copper (II) carbonate solution is created by mixing solid CuCO3 into

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