Wednesday Quiz 5
[3]
1.
Chem 265
2012
What concentration of oxalate is required to precipitate 99.0% of 0.01 M Ce3+ ?
Ksp for Ce2(C2O4)3 = 5.9 x 10-30
Amount remaining = 1.0 %
0.01 *0.01 M Ce3+ remains
For this concentration, [C2O4]3 =
[C2O4] = 8 x 10-8 M
1 sig fig
[1]
2.
Which is the stronger base of the following two?
Urea
Kb = 1.5 x 10-14
Hydrazine
Kb = 1.1 x 10-6
5.9 𝑥 10−30
0.00012
=5.9 x 10-22 M
[2]
3.
If a 0.100 M solution of NaOH is added to a solution containing 0.200 M Ni 2+,
0.200 M Ce3+, and 0.200 M Cu2+, which metal hydroxide will precipitate first? Ksp
for Ni(OH)2 = 6.0 X 10-16, Ksp for Ce(OH)3 = 6.0 X 10-22, and Ksp for Cu(OH)2 =
4.8 x 10-20.
(a) Ni(OH)2
(b) Ce(OH)3
(c) Cu(OH)2
You need to calculate the solubility of each to decide which will ppt first
[1]
4.
What is the pH of a 0.100 molar solution of sodium chloroacetate. Chloroacetic
acid is a moderately weak acid
(a) 1.17 x 10-8
(b) 7.93
(c) 1.93
The salt of a weak acid is basic
[3]
4.
Find the concentration of Ag+ in equilibrium with AgBr(s) and 0.20 M Br-.
Ksp for AgBr = 5.0 x 10-13
Ksp for AgBr = 5.0 x 10-13 = [Ag+] *[Br-]
Let s = solubility = [Ag+]
[Br-] = s +0.20 M ~ 0.20 M
[Ag+] =
5x10−13
0.20
= 25 x 10-13 = 2.5 x 10-12 M