CHMY 143 Sโ10 Exam 3
1. An acid-base equilibrium system is created by dissolving 0.10 mol HF in water to a volume of 1.0 L.
What is the effect of adding 0.050 mol Fโ (aq) to this solution?
a.
The pH of the solution will decrease.
b.
Some Fโ reacts with H3O+, increasing the concentration of HF and reestablishing solution equilibrium.
c.
The addition of Fโ will have no effect on the pH or the concentration of HF.
d.
The ionization of HF increases, increasing the concentration of Fโand decreasing the pH.
e.
The ionization of HF decreases, decreasing the concentration of H3O+ and decreasing the pH.
2. What is the pH of an aqueous solution composed of 0.30 M HF and 0.10 M Fโ? (Ka of HF = 7.2 x 10โ4)
a.
0.477
b.
1.83
c.
2.67
d.
3.62
e.
6.99
3. Which of the following combinations would be best to buffer an aqueous solution at a pH of 9.0?
a.
H3PO4 and H2PO4
โ, Ka1 = 7.5 x 10โ3
b.
HNO2 and NO2
โ, Ka = 4.5 x 10โ4
c.
CH3CO2H and CH3COOโ, Ka = 1.8 x 10โ5
d.
H2PO4
โ and HPO4
2โ, Ka2 = 6.2 x 10โ8
e.
NH4
+ and NH3, Ka = 5.7 x 10โ10
4. Each of the following mixtures can produce an effective buffer solution EXCEPT
a.
HF and NaF.
b.
Na2HPO4 and Na3PO4.
c.
NaHCO3 and Na2CO3.
d.
NaH2PO4 and Na2HPO4.
e.
HCl and KCl.
5. What is the pH of a buffer that results when 0.50 mole of H3PO4 is mixed with 0.25 mole of NaH2PO4 and
diluted with water to 1.00 L? (Acid dissociation constant of H3PO4 : Ka1 = 7.5 x 10โ3)
a.
1.82
b.
2.12
c.
6.91
d.
7.21
e.
12.44
