3. Acids and Bases

Which is a stronger acid?

c. CH₃OCH₂CH₂CH₂OHorCH₃CH₂OCH₂CH₂OH

d.

The pK_a of ascorbic acid (vitamin C, page 55) is 4.17, showing that it is slightly more acidic than acetic acid (CH₃COOH, pK_a 4.74).

c. Compare the most stable conjugate base of ascorbic acid with the conjugate base of acetic acid, and suggest why these two compounds have similar acidities, even though ascorbic acid lacks the carboxylic acid (COOH) group.

Rank the following acids in decreasing order of their acid strength. In each case, explain why the previous compound should be a stronger acid than the one that follows it.

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.

b. Determine which nitrogen atom is the most basic.

Choose the more basic member of each pair of isomers, and show why the base you chose is more basic.

(a)

(b)

The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.

b. Explain why X is a stronger acid than W.

c. Explain why Y is a stronger acid than X.

d. Explain why Z is a stronger acid than Y.

Choose the more acidic member of each pair of isomers, and show why the acid you chose is more acidic.

(a)

(b)

(c)

The following compounds can all react as acids.

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

Consider the type of orbitals involved, and rank the following nitrogen compounds in order of decreasing basicity. 2. Rank the conjugate acids in order of increasing acidity. (Hint: These two orders should be the same!)

Consider each pair of bases, and explain which one is more basic. Draw their conjugate acids, and show which one is a stronger acid.

(a)

(b)

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pKa values, but if you need a hint, you can consult Appendix 4.

a. CH₃CH₂OH + CH₃NH⁻

b. F₃CCOONa + Br₃C—COOH

c. CH₃OH + H₂SO₄

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

b. Rank ethanol, methylamine, and acetic acid in decreasing order of basicity. In each case, show the equation for the reaction with a generic acid (HA) to give the conjugate acid.

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

a. Rank ethanol, methylamine, and acetic acid in decreasing order of acidity. In each case, show the equation for the reaction with a generic base (B:⁻) to give the conjugate base.

Which is a stronger acid?

For each of the following compounds, indicate the atom that is protonated when an acid is added to a solution of the compound.

c.

d.