CHEM 10061 Exam #3 Name_____________________
Date______________________
Equations: pH =
 log [H+], pH = pKa + log Ошибка!
K w
= [H + ][OH

] = 1.0 x 10

14 ,
K a
x K b
= K w
Multiple Choice (3 pts. ea.)
____ 1. Which one of the following is the weakest acid? a. HF (K a
= 6.8 x 10
–4
) c. HNO
2
(K a
= 4.5 x 10
–4
) b. HCN (K a
= 4.9 x 10
–10 d. HClO (K a
= 3.0 x 10
–8
)
)
____ 2.
What is the pH of an aqueous solution at 25°C in which [OH 
] is 0.0025 M? a. 11.4 b. 2.60 c. 2.25 d. 3.40
____ 3. The solubility of PbCl2 is 1.6 x 10–2 mol/L. What is the K sp
of PbCl2?
a. 1.6 x 10–5 b. 3.1 x 10–7 c. 4.1 x 10–6 d. 5.0 x 10–4
____ 4.
What is the concentration of hydronium ions in a solution with pH = 4.282? a. 4.282 M b. 9.718 M c. 1.92 x 10

10 M d. 5.22 x 10

5 M
____ 5.
A substance that is capable of acting as both acid and as base is called: a. autosomal b. conjugated c. amphoteric
____ 6.
K b
for C
5
H
5
N is 1.4 x 10

9 . K a
for C
5
H
5
NH + is: d. autocratic a. 1.0 x 10

7 b. 1.4 x 10

23 c. 7.1 x 10

6 d. 1.4 x 10

5
____ 7. Calculate the molar concentration of bromide ions in a saturated solution of mercury
(II) bromide (HgBr
2
), K sp
= 8.0 x 10–20.
a. 2.7 x 10–7 M b. 5.4 x 10–7 M c. 2.0 x 10–20 M d. 1.4 x 10–10 M
____ 8.
The strength of an acid ______ as the polarity of the R-H bond ______. a. increases, increases c. increases, decreases b. decreases, increases d. none of these
____ 9. Which one of the following is the most acidic? a. H
2
Te b. H
2
Se c. H
2
O
____ 10.
Which of the following acids will be the weakest?
a. H
2
SO
4 b. HSO
4
 c. H
2
SO
3 d. H d. H
2
2
SeO
S
4

____ 11.
Which of the following is the conjugate base of H
2
PO
4

 a. H
3
PO
4 b. HPO
4
 c. PO
4
 d. H
4
PO
4
+
____ 12. Determine the pH of a solution prepared by mixing 50 ml of 0.125 M KOH with
50 ml of 0.125 M HCl.
a. 5.8 b. 6.3
____ 13.
Which of the following is a Lewis acid? c. 7.0 d. 8.1 a. BF
3 b. NH
3 c. OH
 d. Br

____ 14. Which of the following substances, when added to a solution of nitrous acid
(HNO2), could be used to prepare a buffer solution?
d. NaCl a. HCl b. NaNO2 c. HOAc
____ 15. What is the pH of a 0.025 M nitric acid (HNO
3
) solution? a. 13.8 b. 0.025 c. 12.4
____ 16.
Which definition of acids and bases is the most general? a. Arrhenius b. Lewis c. Brønsted-Lowry
____ 17. Of the following, which solution has the greatest buffering capacity?
d. 1.6 d. Fenk a. 0.121 M HF and 0.667 M NaF c. 0.821 M HF and 0.909 M NaF b. 0.821 M HF and 0.217 M NaF d. 0.100 M HF and 0.217 M NaF
____ 18. According to Arrhenius, an acid is a substance that; a. is capable of donating one or more protons b. causes an increase in the concentration of hydronium ion in aqueous solutions c. can accept a pair of electrons to form a coordinate covalent bond d. reacts with the solvent to form the cation formed by autoionization of that solvent
____ 19. Consider a solution prepared by adding NaOAc to an aqueous solution of HOAc.
(Ka = 1.8 x 10–5) If a small amount of HCl is added to this buffer solution, the pH of the solution will drop slightly. The pH does not drastically decrease because the
HCl reacts with the ________ present in the buffer solution.
a. H2O b. H+ c. HOAc d. OAc–
____ 20.
The point in a titration where stoichiometric quantities of acid and base have reacted is called the: a. endpoint c. indicator point b. equivalence point d. point of no return

Solve the following problems showing all work. Use complete sentences for essay questions. Remember to use proper units, significant figures and rounding.
1. Calculate the pH of a solution containing 0.818 M acetic acid (HOAc) (Ka = 1.76 x 10–5) and 0.172 M sodium acetate (NaOAc). (10 pts.)
2. Consider the titration of 50.0 mL of 0.215 M HBrO (Ka = 2.0 x 10–9) with 0.250 M NaOH.
Calculate the pH of the solution after addition of 43.0 mL of NaOH solution. (10 pts.)

3. Describe how buffer solutions are prepared (the components) and how they work to keep pH constant when small quantities of acid or base are added to the solution. (10 pts.)
4. Calculate the pH for a saturated solution of zinc hydroxide, Zn(OH)
2
. K sp
= 1.2 x 10–17
(10 pts.).