3. Acids and Bases

Give the products of the following acid–base reactions and indicate whether reactants or products are favored at equilibrium.

b. CH₃CH₂OH + ^-NH₂ ⇌

Show how you would use extractions with a separatory funnel to separate a mixture of the following compounds: benzoic acid, phenol, benzyl alcohol, aniline

Complete the following proposed acid–base reactions, and predict whether the reactants or products are favored.

(a)

(b)

Phenols are less acidic than carboxylic acids, with values of pK_a around 10. Phenols are deprotonated by (and therefore soluble in) solutions of sodium hydroxide but not by solutions of sodium bicarbonate. Explain how you would use extractions to isolate the three pure compounds from a mixture of p-cresol (p-methylphenol), cyclohexanone, and benzoic acid.

Would amide or acetate most easily deprotonate an alcohol to make the alkoxide anion? Calculate K_eq for each possibility.

For each of the following acid–base reactions, (i) predict which side of the reaction you expect to be favored. If a pK_a is not one of the ten common ones we learned in Chapter 4, it will be given to you.

(a)

Which of the following reactions favor formation of the products? Recall that the equilibrium favors formation of the weaker acid.

For each of the following compounds, indicate the pH at which

b. more than 99% of the compound is in a form that possesses a charge.

    1. CH₃CH₂COOH (pK_a = 4.9)

    2. CH₃N⁺H₃ (pK_a = 10.7)

Ethyne (HC≡CH) has a pK_a value of 25, water has a pK_a value of 15.7, and ammonia (NH3) has a pKa value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne with

a. HO^-.

Given the value of K_eq for the following acid–base reactions, identify the weakest acid and the weakest base.

(a)

Predict the products of the following acid–base reactions, or indicate if no significant reaction would take place.

a. H—C≡C—H + NaNH₂

b. H—C≡C—H + CH₃Li

c. H—C≡C—H + NaOCH₃

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. 

c.

d.

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)

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