1) Of the following, which is the best base to create a buffer with a pH = 4.5?

Question

1) Of the following, which is the best base to create a buffer with a pH = 4.5?

a) Pyridine, Kb = 1.7x10^-9

b) Ethylamine, Kb = 6.4x10^-4

c) Hydrazine, Kb = 1.3x10^-6

d) Aniline, Kb = 4.3x10^-10

2) Of the following, which is the best base to create a buffer with a pH = 8.0?

- Hydrazine, Kb = 1.3x10^-6

- Pyridine, Kb = 1.7x10^-9

- Ethylamine, Kb = 6.4x10^-4

- Aniline, Kb = 4.3x10^-10

3) At which point along the titration curve of a weak acid titrated with a strong base does the pH = pKa

a) At the half equivalence volume

b) At the equivalence volume

c) Before any base is added

d) Beyond the equivalence volume

4) In what pH range will the following titrations have their equivalence points?

- Weak acid with a strong base a) pH is greater than 7 at the equivalence

- Weak base with a strong acid b) pH is less than 7 at equivalence point

- Strong base with a strong acid c) pH equals 7 at the equivalence point

Explanation / Answer

for any basic buffer

pOh = pKb + log [salt] / [base]

1) option d) Aniline, Kb = 4.3x10^-10

2) option a  Hydrazine, Kb = 1.3x10^-6

at half equivalent point [salt] = [acid] so

pH = pKa

3) a) At the half equivalence volume

4)  Weak acid with a strong base = a) pH is greater than 7 at the equivalence

Weak base with a strong acid = b) pH is less than 7 at equivalence point.

- Strong base with a strong acid = c) pH equals 7 at the equivalence point .

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