3. Acids and Bases

For the bases shown, draw the conjugate acid and identify a pK_a value from Table 4.5 that would help you accurately estimate its stability.

(d)

For each indicated proton, suggest an approximate pK_a value from Table 4.5. Rationalize your choice.

(b)

Does methanol behave as an acid or a base when it reacts with methylamine?

Which of the following compounds has the lowest $pKa$ value?

Why is imidazole a stronger acid (pK_a ~ 14.4) than pyrrole (pK_a ~ 17)?

Which is a stronger base: ethoxide ion or acetate ion? Give pK_b values (without looking them up) to support your choice.

Peroxyacetic acid (pK_a = 8.2) is a much weaker acid than acetic acid (pK_a = 4.74). Explain why peroxyacetic acid is a weaker acid than acetic acid.

Butyric acid, the compound responsible for the unpleasant odor and taste of sour milk, has a pK_a value of 4.82. What is its Ka value? Is it a stronger acid or a weaker acid than vitamin C?

Which of the following molecules contains a hydrogen atom with a $pKa$ value between $20$ and $25$?

Hydrogen gas (H₂) has a relatively high pK_a value. Is it a stable or unstable acid? Do you expect it to participate in acid–base reactions?

In the context of acid-base chemistry, what does the $p$ in $p{K}_a$ represent?

The K_a of phenylacetic acid is 5.2 × 10⁻⁵, and the pK_a of propionic acid is 4.87.

a. Calculate the pK_a of phenylacetic acid and the K_a of propionic acid.

b. Which of these is the stronger acid? Calculate how much stronger an acid it is.

The following compounds can all react as bases.

c. Rank the original compounds in order, from strongest base to weakest base.

For each indicated proton, suggest an approximate pK_a value from Table 4.5. Rationalize your choice.

(d)

Given the data in Problem 47:

b. What pH would you make the water layer to cause the carboxylic acid to dissolve in the water layer and the amine to dissolve in the ether layer?