Need help with both a and b please! Ks0 for gypsum (CaSO442H2O) IS 10-4.61, and
ID: 282975 • Letter: N
Question
Need help with both a and b please!
Ks0 for gypsum (CaSO442H2O) IS 10-4.61, and Ks0 for anhydrite (CaSO4) is 10-4.36.
(a) Which mineral phase controls the solubility of Ca2+ in brine containing Ca2+ and SO42-?
(b) Suppose a piece of sheetrock (drywall), which is essentially gypsum covered by paper, fell off a truck during a rainstorm, broke into pieces and landed in a parking lot in a depression filled with rainwater. What is the maximum concentration of Ca2+ and SO42- that could occur in the water if it reaches equilibrium with the gypsum in the sheet?
Explanation / Answer
(a) Which mineral phase controls the solubility of Ca2+ in brine containing Ca2+ and SO42-?
Halite mineral controls the solubility of Ca2+ in brine containing Ca2+ and SO42
(b) Suppose a piece of sheetrock (drywall), which is essentially gypsum covered by paper, fell off a truck during a rainstorm, broke into pieces and landed in a parking lot in a depression filled with rainwater. What is the maximum concentration of Ca2+ and SO42- that could occur in the water if it reaches equilibrium with the gypsum in the sheet?
Calcium sulfate, CaSO4, given that its Ksp is 2.4 x 10-5.
The dissolution of calcium sulfate forms equal amounts of calcium ions and sulfate ions according to the following equation.
CaSO4(s) Ca+2 (aq) + SO4 -2 (aq)
If we let [Ca+2] = [SO4 -2] = x , then we can solve for the Molarity of calcium sulfate that would be soluble.
Ksp = [Ca+2][SO4 -2]
2.4 x 10-5 = (x)(x)
solving for x we get [Ca+2] = [SO4 -2] = 4.90 x 10-3 M
Since the equation above shows a 1:1 mole ratio of calcium sulfate to Ca+2 ions, we can assume that 4.90 x 10-3 moles of CaSO4 will dissolve. Since CaSO4 has a mass of 136.1 g/mol, this would equate to:
(4.90 x 10-3 mol/L) x (136.1 g/mol) = 6.67 x 10-1 grams/L