Solid sodium carbonate is slowly added to 175 mL of a 0.0676 M calcium nitrate s

Question

Solid sodium carbonate is slowly added to 175 mL of a 0.0676 M calcium nitrate solution. What is the concentration of carbonate ion required to just initiate precipitation? Solid ammonium carbonate is slowly added to 125 mL of a iron(ll) acetate solution until the concentration of carbonate ion is 0.0233 M. What is the maximum amount of iron(II) ion remaining in solution? Consider the insoluble compound silver bromide, AgBr. The silver ion also forms a complex with cyanide ions. Write a balanced net ionic equation to show why the solubility of AgBr (s) increases in the presence of cyanide ions and calculate the equilibrium constant for this reaction. For Ag(CN)_2^-, K_f = 5.6 times 10^18 .

Explanation / Answer

Q20.

Na2CO3 reacts with Ca(NO3)2 as:

Na2CO3 (aq) + Ca(NO3)2 (aq) ----------> CaCO3 (s) + 2NaNO3 (aq)

CaCO3 ionises as:

CaCO3 (s) <-------> Ca2+ + CO32-(aq)

Ksp = [Ca2+ ][CO32-] = 3.39 X 10-9   (Ksp was not given so we used a value given in common literature)

Or Ksp = [0.0676 ][CO32-] ======1)

[Ca2+ ] = 0.0676M; Because Calcium nitrate ionises completely as:

Ca(NO3)2 (s) -------> Ca2+(aq) + 2 NO3-(aq)

When ionic product Kip of CaCO3 exceeds Ksp the precipitation will occur.

Rearranging equation1)

[CO32-] = 3.39 X 10-9 / 0.0676 = 5.0 X 10-8M

Hence precipitation will just begin when the carbonate ion concentration is equal to 5.0 X 10-8M

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