Question

The Ksp of Ag2SO4 is 1.4 X 10-5. Would you have expected to obtain a precipitate of Ag2SO4 in any of the experiments that you did while determining how you were going to test for chloride ion? Justify your answer with a calculation.

The Cl- Test A) Place several drops of sample solution in vial and add 1M HNO3 until solution is acidic (test acidity with red litmus paper) B) Add one drop of 0.02M AgNO3 C) If cloudy ppt. forms, then Cl- is present

Answer 1

Ag₂SO₄(s) ---- > 2Ag⁺(aq) + SO₄^2-(aq), Ksp = 1.4 x 10^-5

We added 1 one drop(1 mL) of 0.02M AgNO3.

Hence moles of Ag⁺(aq) added = MxV = 0.02M x 1.0 x 10^-3 L = 2.0 x 10^-5 mol

If the final volume of the solution after addition of sample solution, HNO3 and AgNO3 is 10 mL, the concentration of Ag⁺(aq), [Ag⁺(aq)] = 2.0 x 10^-5 mol / 10 x 10^-3 L = 2.0 x 10^-3 M

Also the sulphate ion concentration would be of the same order.

Hence ionic product, IP = [Ag⁺(aq)]²x[SO₄^2-(aq)] < Ksp (1.4 x 10^-5)

However for precipitation to occur IP should be greater than Ksp. Hence precipitation will not occur.