Question

Sodium sulfate is slowly added to a solution containing 0.0500 M Ca2 (aq) and 0.0220 M Ag (aq). What will be the concentration of Ca2 (aq) when Ag2SO4(s) begins to precipitate? Solubility-product constants. (can be found here: https://sites.google.com/site/chempendix/Ksp )

[Ca^2+] = __________ M

Answer 1

Sodium sulfate = Na2sO4

[CA+2] = 0.05 M

[Ag+] = 0.022 M

find Ca+2 when Ag2SO4 precipitates

so

first, identify [SO4-2] required for precipitation

for

Ag2SO4 <-> 2Ag+ + SO4-2

Ksp = [Ag+]^2[SO4-2]

1.20×10^–5 = (0.022)^2*(SO4-2)

[SO4-2] = (1.2*10^-5)/(0.022^2)

[SO4-2] = 0.024793 M

when [SO4-2] = 0.024793 is added, it starts to precipitate

so

for Ca+2:

Ksp = [Ca2+][SO4-2]

[SO4-2] = 0.024793

4.93×10^–5 = [Ca+2] (0.024793)

[Ca+2] = (4.93*10^-5)/(0.024793) = 0.001988 M