Acid-Base Equilibria And Buffer Solutions Worksheet With Answers Page 5
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5Chem 1B
Chapter 15 Exercises
–
5
3.
In a third acid-base titration, 40.0 mL of 0.100 M ammonia (NH
, K
= 1.8 x 10
) is titrated with 0.100
3
b
M HCl solution. Determine the pH of the base solution:
(a) before HCl is added;
(b) after 20.0 mL of 0.100 M HCl is been added;
(c) after 30.0 mL of 0.100 M HCl is added;
(d) after 40.0 mL of 0.100 M HCl is added.
(e) after 45.0 mL of 0.100 M HCl is added.
(f) after 50.0 mL of 0.100 M HCl is added.
(Answers: (a) pH = 11.13; (b) pH = 9.25; (c) pH = 8.77; (d) pH = 5.28;
(e) pH = 2.23; (f) pH = 1.95)
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5
4.
What is the pH of the resulting solution if 40.0 mL of 0.100 M ammonia (NH
, K
= 1.8 x 10
) is added
3
b
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to 40.0 mL of 0.100 M acetic acid (CH
COOH, K
= 1.8 x 10
)?
3
a
(Answer: pH = 7.00)
5.
50.0 mL of 0.0500 M KHP (potassium hydrogen phthalate, KHC
H
O
) was titrated with NaOH
8
4
4
solution of unknown concentration and the pH of the solution was measured during titration. It required
23.20 mL of NaOH solution to reach equivalent point and the solution had a pH of 5.30 after 11.6 mL
of NaOH was added. (a) Calculate the molar concentration of NaOH and the K
of KHP. (b) What is the
a
2
–
K
of KHP? (c) What is the K
of the phthalate ion, C
H
O
? (d) Calculate the expected pH at
a
b
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equivalent point.
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–
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9
(Answer: (a) [NaOH] = 0.108 M; (b) K
= 5.0 x 10
; (c) K
= 2.0 x 10
; (d) pH = 8.92)
a
b
6.
Which indicator(s) is/are suitable for the titration of: (a) HCl with NaOH; (b) CH
COOH with NaOH,
3
and (c) NH
with HCl?
3
–
–
–
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5
8
Available indicators are: Methyl Orange (K
~ 10
); Methyl Red (K
~ 10
); Phenol Red (K
~ 10
),
a
a
a
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9
and Phenolphthalein (K
~ 10
)
a
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