3. Acids and Bases

Predict the K_eq for the following acid–base reaction.

How do you know that a proton with a low pK_a value is acidic (besides 'I just remember')?

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 acid–base reactions, (ii) calculate K_eq. If a pK_a is not one of the ten common ones we learned in Chapter 4, it will be given to you.

(a)

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 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

The pK_a of a protonated alcohol is about -2.5, and the pK_a of an alcohol is about 15. Therefore, as long as the pH of the solution is greater than _______ and less than _______, more than 50% of 2-propanol (the product of the reaction on p. 244) will be in its neutral, nonprotonated form.

Given that the indicated pK_a values correspond to the acid dissociation reactions shown, calculate the ratio of acid to conjugate base for the reactions shown.

(b)

The pK_a of protonated acetone is about –7.5 and the pK_a of protonated hydroxylamine is 6.0.

a. In a reaction with hydroxylamine at pH 4.5 (Figure 16.2), what fraction of acetone is present in its acidic, protonated form?

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Calculate K_eq for these acid–base reactions.

(c)

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)

Calculate K_eq for the following acid–base reactions.

(b)

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

Estimate the K_eq for the following reactions based on the stability of the anions involved.

(b)