3. Acids and Bases

Citrus fruits are rich in citric acid, a compound with three COOH groups. Explain the following:

b. The third pK_a is greater than the pKa of acetic acid.

Given the structure of ascorbic acid (vitamin C):

(a) Is ascorbic acid a carboxylic acid?

(b) Compare the acid strength of ascorbic acid (pK_a = 4.71) with acetic acid.

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

Given the structure of ascorbic acid (vitamin C):

(c) Predict which proton in ascorbic acid is the most acidic.

(d) Draw the form of ascorbic acid that is present in the body (aqueous solution, pH = 7.4)

Arrange the following compounds in order of decreasing acidity.

CH₃COOH, CH₃OH, CH₃CH₃, CH₃SO₃H, CH₃NH₂, CH₃SH, CH₃C≡CH

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

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.

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

(a)

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

Which of the following bases can remove a proton from a terminal alkyne in a reaction that favors products?

You are planning to carry out a reaction that produces protons. The reaction will be buffered at pH = 10.5. Would it be better to use a protonated methylamine/methylamine buffer or a protonated ethylamine/ethylamine buffer? (pK_a of protonated methylamine = 10.7; pK_a of protonated ethylamine = 11.0)

Any base whose conjugate acid has a pK_a greater than ______ can remove a proton from a terminal alkyne to form an acetylide ion (in a reaction that favors products).