1. Unit 13: Buffers And 2 Mini-labs
Lecture Presentation
Unit 13: Buffers
And 2 Mini-labs
© 2015 Pearson Education, Inc.

2. WARM UP TAKE OUT: Lab Notebook
BE READY: To hear about your tasks for each mini-lab
TIME: 1 minute

3. Agenda Distillation Demo Mini-Lab: Properties of Buffers
Mini-Lab: Paper Chromatography

4. Mini-Labs
COMPLETE: Both Mini-Labs TIME: Until 9:35 WHEN DONE: With both labs, attempt post-lab questions and additional buffer practice problems

5. Adding bromide ion to a saturated aqueous solution of _______ decreases its solubility in water.
BaSO4
Li2CO3
PbS
d. AgBr
Answer: d

6. HCl and KCl HNO3 and KNO3 HCl and NH4Cl d. NH3 and NH4Cl
Which of the following mixtures could be used to prepare an effective buffer solution?
HCl and KCl
HNO3 and KNO3
HCl and NH4Cl
d. NH3 and NH4Cl
Answer: d

7. Which solution has the greatest buffer capacity?
1 L of solution containing 0.1 M NH3 and 0.1 M NH4Cl
1 L of solution containing 0.05 M NH3 and 0.05 M NH4Cl
1 L of solution containing 0.1 M NH3 and 0.01 M NH4Cl
d. 1 L of solution containing 0.5 M NH3 and 0.5 M NH4Cl
Answer: d

8. Select the best acid or base to pair with its conjugate salt to prepare a buffer with pH ≈ 8.5.
acetic acid, Ka = 1.8 x 10−5
ammonia, Kb = 1.8 x 10−5
hydroxylamine, Kb = 1.1 x 10−8
citric acid, Ka = 7.4 x 10−4
Answer: c

9. For HCN, Ka = 4.9  10−10. What is the pH of a buffer solution in which [HCN] = 0.100 M = [KCN]?
4.7
7.0
9.3
d. 14.0
Answer: c

10. For HCN, Ka = 4. 9  10−10. [HCN] = 0. 100 M, [KCN] = 0
For HCN, Ka = 4.9  10−10. [HCN] = M, [KCN] = M, pH of buffer solution = _____.
7.0
9.0
9.3
d. 9.6
Answer: d

11. For HCN, Ka = 4. 9  10−10. [HCN] = 1. 00 M, [KCN] = 0
For HCN, Ka = 4.9  10−10. [HCN] = 1.00 M, [KCN] = M, pH of buffer solution = _____.
7.0
8.3
9.0
d. 9.3
Answer: b

12. Ka = [H+][A−] Kw = [H+][OH−] = 10−14 pH = pKa + d. pKa = pH +
Select the correct representation of the Henderson-Hasselbach equation?
Ka = [H+][A−]
Kw = [H+][OH−] = 10−14
pH = pKa +
d. pKa = pH +
Answer: c

13. When titrating a weak base with a strong acid, a good indicator to use would be
methyl red (color change at pH = 5).
b. bromothymol blue (change at pH = 7).
c. phenolphthalein (change at pH = 9).
d. None of the above
Answer: a

14. When titrating a weak acid with a strong base, a good indicator to use would be
a. methyl red (color change at pH = 5).
bromothymol blue (change at pH = 7).
phenolphthalein (change at pH = 9).
d. None of the above
Answer: c

15. For BaCO3, Ksp = 5.0  10−9. What is [Ba2+] in a saturated aqueous solution of BaCO3?
7.1  10−5 M
1.0  10−8 M
2.5  10−9 M
d. 5.0  10−9 M
Answer: a

16. For BaF2, Ksp = 1.7  10−6. What is [Ba2+] in a saturated aqueous solution of BaF2?
1.7  10−6 M
3.4  10−6 M
7.6  10−3 M
d. 1.5  10−2 M
Answer: c

17. [Ag+][SO42−] [Ag+]2[SO42−] [Ag+] [SO42−]2 d. (2[Ag+])2[SO42−]
Select the correct Ksp expression for the dissolution of silver sulfate, Ag2SO4.
[Ag+][SO42−]
[Ag+]2[SO42−]
[Ag+] [SO42−]2
d. (2[Ag+])2[SO42−]
Answer: b

18. For BaF2, Ksp = 1.7  10−6. What is [F1−] in a saturated aqueous solution of BaF2?
1.7  10−6 M
5.7  10−5 M
7.6  10−3 M
d. 1.5  10−2 M
Answer: d

19. For BaF2, Ksp = 1.7  10−6. If KF is added to a saturated solution so that [F1−] = 0.10 M, what is [Ba2+]?
1.7  10−6 M
1.7  10−5 M
1.7  10−4 M
d. 1.7  10−3 M
Answer: c

20. Ag(NH3)21+ Ag(NH3)2+ NH3Br1− d. NH4Br
Silver bromide is insoluble in water, but dissolves in aqueous ammonia, due to the formation of _______.
Ag(NH3)21+
Ag(NH3)2+
NH3Br1−
d. NH4Br
Answer: a

21. Which ion will precipitate first when sulfide ion is added to a solution containing all of the ions below?
Hg2+
Pb2+
Zn2+
d. Cd2+
Answer: a

22. Which ion will precipitate when HCl is added to a solution containing all of the ions below?
Zn2+
Pb2+
Al3+
d. Ba2+
Answer: b

23. Which ion will precipitate when phosphate ion is added to a solution containing all of the ions below?
K1+
Ba2+
Na1+
d. NH41+
Answer: b

24. Which ion will form a precipitate upon addition of chloride ion, hydrogen sulfide, ammonium sulfide, or ammonium hydrogen phosphate?
Ba1+
Na2+
K1+
d. NH41+
Answer: a