3. Acids and Bases

Consider the following proposed Brønsted–Lowry acid–base reactions. In each case, draw the products of a transfer of the most acidic proton on the acid to the most basic site on the base. Use Appendix 4 to find or estimate the pK_a values for the acids and the pK_b values for the bases. Then determine which side of the reaction is favored, either reactants or products.

(a)

(b)

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

c. Predict whether the following equilibrium will favor the reactants or the products.

Write equations for the following acid–base reactions. Use the information in Table 2-2 or Appendix 4 to predict whether the equilibrium will favor the reactants or the products.

a. HCOOH + ^–CN

b. CH₃COO^– + CH₃OH

c. (CH₃)₂CHOH + NaNH₂

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them.

a. CH₃Li + H—C≡C—H → CH₄ + H—C≡CLi

b. CH₃Li + (CH₃)3C—OH → CH₄ + (CH₃)₃C—OLi

For each of the following pairs of reactions, indicate which one has the more favorable equilibrium constant (that is, which one most favors products):

1.

2.

From which of the following compounds can HO⁻ remove a proton in a reaction that favors product formation?

How could you separate a mixture of the following compounds? The reagents available to you are water, ether, 1.0 M HCl, and 1.0 M NaOH.

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

HO⁻ CH₃NH₂ HC≡C⁻  CH₃OH H₂O Cl⁻