An industrial plant processes its waste water through a sedimentation tank that removes hazardous metals by precipitating them as insoluble carbonate salts. If sodium carbonate is gradually added to the tank, what would be the order of precipitation of the metals, Pb2+, Cu2+, Hg22+, and Zn2+ if each is 1.0 104 M? ( Ksp PbCO3 = 7.4 1014, Ksp CuCO3 = 1.4 1010, Ksp Hg2CO3 = 8.9 1017, and Ksp ZnCO3 = 1.4 1011)
a.
Pb2+, Hg22+, Zn2+, Cu2+
b.
Hg22+, Pb2+, Zn2+, Cu2+
c.
Cu2+, Zn2+, Pb2+, Hg22+
d.
Cu2+, Zn2+, Hg22+, Pb2+
e.
All metal ions will precipitate at the same time.
Question 2
A solution is 0.010 M in each of Pb(NO3)2, Mn(NO3)2, and Zn(NO3)2. Solid NaOH is added until the pH of the solution is 8.50. Which of the following statements is true?
Salt
Ksp
Pb(OH)2
1.4 1020
Mn(OH)2
2.0 1013
Zn(OH)2
2.1 1016
a.
No precipitate will form.
b.
Only Pb(OH)2 will precipitate.
c.
Only Mn(OH)2 will precipitate.
d.
Only Zn(OH)2 and Pb(OH)2 will precipitate.
e.
All three hydroxides will precipitate.
Water-soluble organic molecules.
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