CHEMISTRY 2 HELP?

[匿名]

2020-04-05 11:21 pm

1. Which of the following mixtures would not be a good buffer
a. HNO3/ NaNO3
b. HF/LiF
c. CH3COOH/ CH3COONa
d. H2SO3/ NaHSO3
e. all of these are good buffers

2. Calculate the ph of a soln that is 0.322 M in nitrous acid (HNO2) and 0.178 M in potassium nitrite (KNO2). the acid dissociation constant of nitrous is 4.50x10^-4
a. 10.91
b. 3.093
c. 14.26
d. 3.607
e. 4.554

3. Calculate the ph of a buffer that is 0.105 M HC2H3O2 and 0.146 M KC2H3O2. The Ka for HC2H3O2 is 1.8x10^-5
a. 4.89
b. 9.11
c. 5.25
d. 4.74
e. 4.60

4. What is the ph of a buffer soln that is 0.192 M in lactic acid and 0.155 M in sodium lactate? The Ka of lactic acid is 1.4x10^-4
a. 5.48
b. 3.76
c. 10.24
d. 3.94
e. 14.09

回答 (1)

pingshek

2020-04-06 12:11 am

✔ 最佳答案

1.
All of the options b, c and d are the mixtures of a weak acid and its conjugate base. Hence, options b, c and d would be good buffers.
HNO₃ in option a is a strong acid, which cannot be used in making a buffer.

The answer: a. HNO₃ / NaNO₃

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2.
Henderson-Hasselbalch equation:
pH = pKa + log([NO₂⁻]/[HNO₂])
pH = -log(4.5 × 10⁻⁴) + log(0.178/0.322) = 3.089

The answer: b. 3.093 (The closest answer)

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3.
Henderson-Hasselbalch equation:
pH = pKa + log([C₂H₃O₂⁻]/[HC₂H₃O₂])
pH = -log(1.8 × 10⁻⁵) + log(0.146/0.105) = 4.89

The answer: a. 4.89

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4.
Henderson-Hasselbalch equation:
pH = pKa + log([lactate ion]/[lactic acid])
pH = -log(1.4 × 10⁻⁴) + log(0.155/0.192) = 3.76

The answer: b. 3.76

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