Radioactive Decay And Acid Dissociation Constant Chap. 9 And 10 Worksheet With Answers - Middle Tennessee State University Page 12
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209.117 Which of the following weak acids and its conjugate base would you use to
make a buffer with a pH of 5.00? Explain your reasons. Acetic acid, nitrous acid,
or formic acid.
Solution
The best buffer capacity is when the pH equals the pK
. The closer the pH Is
a
to pK
, the higher the buffer capacity. Since pK
for acetic acid is the closest
a
a
to 5.00, a mixture of acetic acid and acetic ion would be best.
9.119 Calculate the pH of the buffers with the acid and conjugate base concentrations
listed below.
2 -
3 -
a) [HPO
]= 0.33 M, [PO
] = 0.52 M
4
4
-
b) [HNO
]= 0.029M, [NO
]= 0.065 M
2
2
-
2 -
[HCO
] = 0.50 M, [CO
]= 0.15 M
c)
3
3
Solution
2 -
b) pK
forHNO
= 3.33
a) pK
forHPO
= 12.66
a
a
2
4
0.52 = 12.86
0.065 = 3.68
pH = 12.66 + log
pH = 3.33 + log 0.029
0.33
-
c) pK
for HCO
= 10.25
a
3
0.15 = 9.73
pH = 10.25 + log
0.50
9.121 A citric acid-citrate buffer has pH = 3.20. You want to increase the pH to a value
of 3.35. Would you add citric acid or sodium citrate to the solution? Explain.
Solution
Add sodium citrate. There are at least two viable explanations: (1) to
increase pH, add the Br
nsted base, citrate; or (2) in Equation 9.54, if the
Ø
-
[B
] increases, the value of the log term increases, which increases pH.
ADDITIONAL EXERCISES
9.123 Consider the following dissociation reaction of a weak acid, HA:
It was determined that 2.63% of the acid in a 0.150 M solution of HA in water
was dissociated. Calculate the pH of the 0.150 M solution.
Solution
9.125 When sodium metal, Na, reacts with water, hydrogen gas, H
, and sodium
2
hydroxide, in solution are produced. Write a balanced equation for the reaction,
and explain how a basic solution is produced.
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