Answer each of the following questions regarding BaSO 4 (Ksp = 1.1 X 10 -11 ) a)

Question

Answer each of the following questions regarding BaSO4 (Ksp = 1.1 X 10-11)

a) For a saturated solution of barium sulfate, what is the molar concentration of Ba2+ if activity coeffecients are ignored?

b) In which of the following solutions will barium sulfate be the most soluble and WHY: 0.25 M sodium sulfate, 0.25 M barium chloride, 0.25 M potassium nitrate

c) Sulfate ion is a weak base. Will raising the pH of the solution of saturated barium sulfate increase the molar solubility of barium sulfate or decrease the molar solubility? WHY?

Explanation / Answer

a) For a saturated solution of barium sulfate, what is the molar concentration of Ba2+ if activity coeffecients are ignored?

Solution :-

BaSO4 ------- > Ba^2+    + SO4^2-

                           x                     x

ksp = [Ba^2+][SO4^2-]

1.1*10^-11 = [x][x]

1.1*10^-11 = [x]^2

Taking square root of both sides we get

3.32*10^-6 =x

So the molar concentration of the Ba^2+ = 3.32*10^-6 M

b) In which of the following solutions will barium sulfate be the most soluble and WHY: 0.25 M sodium sulfate, 0.25 M barium chloride, 0.25 M potassium nitrate

Solution :- Barium sulfate will be more soluble in the 0.25 M potassium nitrate because it do not contain any common ion with the barium sulfate.

c) Sulfate ion is a weak base. Will raising the pH of the solution of saturated barium sulfate increase the molar solubility of barium sulfate or decrease the molar solubility? WHY?

Solution : -

Increasing pH means increasing the concentration of the OH- therefore as the pH increase then it will decrease the solubility of the BaSO4. Since BaSO4 is weakly basic means when it dissociates then it forms HSO4- and OH-

So increasing the pH causes the OH- to increase which is common ion so it will decrease the solubility of the BaSO4

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