Question

Please answer only number 7. number 6 is only there to assist in answering number 7

Problem 6.One-half gram of solid calcium sulfate, CaSO4 (s) is added to 1.0 L of pure water. Immediately the solid begins to dissolve according to the following reaction: CaSO4 (s) <=> Ca+2 + SO4-2 and the Ksp = 2 × 10-5. What is the concentration of dissolved sulfate [SO4-2] in the water once equilibrium is achieved? (hint: your SO4-2 is the lesser of what Ksp allows, or what you added). Do you have solid left?

Problem 7. Repeat problem 6, but this time, you added 0.5 g of CaSO4and 0.5 g of Na2SO4(which completely ionizes into Na+ and SO4-2). How much dissolved SO4-2, dissolved Ca+2, and CaSO4 (solid) exists at equilibrium? (Hint: Set up an equation in which X is the amount of CaSO4 that dissolves out of the solid. Yourequilibrium sulfate is thus what is added from Na2SO4 (converted to M) + X. Your equilibrium Ca+2 is simply X, since it all comes from dissolution. Assuming solid is left, your Ksp can then be used to calculate X. X is then the amount of Ca+2, the amount of solid left is 0.5 g of CaSO4(converted to M) minus X (the amount that dissolved), and the amount of SO4-2 is 0.5 g Na2SO4(converted to M) plus X. the amount from the dissolution. No need for charge balances or Kw in this problem.

Answer 1