3. Acids and Bases

At what pH is the concentration of a compound, with a pK_a = 8.4, 100 times greater in its acidic form than in its basic form? At what pH is 50% of a compound, with a pK_a = 7.3, in its basic form?

If an acid with a pK_a of 5.3 is in an aqueous solution of pH 5.7, what percentage of the acid is present in its acidic form?

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH = 5.5:

i. HON⁺H₃ (pK_a = 6.0)

Calculate K_eq for the following acid–base reaction.

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH = 5.5:

g. HNO₂ (pK_a = 3.4)

h. HNO₃ (pK_a = −1.3)

As long as the pH is not less than ___________, at least 50% of a protonated amine with a pK_a value of 10.4 will be in its neutral, nonprotonated form.

Indicate whether a protonated amine (RN⁺H₃) with a pKa value of 9 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.

1. pH = 1

2. pH = 3

3. pH = 5

4. pH = 7

5. pH = 10

6. pH = 13

For each of the following compounds, indicate the pH at which

a. 50% of the compound is in a form that possesses a charge.

1. CH₃CH₂COOH (pK_a = 4.9)

2. CH₃N⁺H₃ (pK_a = 10.7)

For each of the following compounds, draw the form that predominates at pH = 3, pH = 6, pH = 10, and pH = 14:

a. CH₃COOH (pK_a = 4.8)

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH = 5.5:

e. ⁺NH4 (pK_a = 9.4)

f. HC≡N (pK_a = 9.1)

Indicate whether an alcohol (ROH) with a pK_a value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.

1. pH = 1

2. pH = 3

3. pH = 5

Indicate whether an alcohol (ROH) with a pK_a value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.

3. pH = 7

4. pH = 10

5. pH = 13

A naturally occurring amino acid such as alanine has a group that is a carboxylic acid and a group that is a protonated amine. The pK_a values of the two groups are shown.

d. Draw the structure of alanine in a solution at pH = 12.

For the following acid–base reaction, (c) calculate the ratio of butan-2-ol to 2-butoxide.

What percent of imidazole is protonated at physiological pH (7.4)?