I can not figure out the problems below. Could someone show e step by step how t

Question

I can not figure out the problems below. Could someone show e step by step how to do them? THANKS!

Potassium hydroxide is used to precipitate each of the cations from their respective solution. Determine the minimum concentration of KOH required for precipitation to begin in each case.

1. 1.9X10-2M CaCl2

2. 3.0X10-3M Fe(NO3)2

3. 1.5X10-3M MgBr2

AND........................

Consider a solution that is 1.5X10-2M in Ba2+ and 1.8X10-2M in Ca2+. What minimum concentration of Na2SO4 is required to cause the precipitation of the cation that precipitates first?

Explanation / Answer

a) CaCl2 + 2KOH --> Ca(OH)2 + 2KCl
Ca(OH)2 <=> Ca^2+ + 2OH^-
ksp = 1.9*10^-2 + x^2
4.68*10^-6 = 1.9*10^-2 + x^2
x= [KOH] = 0.01566

b) Fe(NO3)2 +2 KOH--> Fe(OH)2 + 2KNO3
Fe(OH)2 <=> Fe^2+ + 2OH^-
ksp = 3*10^-3 + x^2
4.87*10^-17 = 3*10^-3 + x^2
x= 1.27*10^-10

c) MgBr2 + KOH --> Mg(OH)2 + 2KBr
Mg(OH)2 <=> Mg^2+ + 2OH^-
ksp = 1.5*10^-3 + x^2
2.06*10^-13 = 1.5*10^-3 + x^2
x= 1.17*10^-8

Ba2+ will precipitate first

5.1 x 10-9 = 0.015 [SO42-]

[[SO42-] =3.4 x 10^-7 M

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