3. Acids and Bases

(••) For the following acid–base pairs,

(iii) predict the favored side of equilibrium;

(e) <IMAGE>

Ethyne (HC≡CH) has a pKa value of 25, water has a pKa 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 

b. −NH2.

c. Which would be a better base to use if you wanted to remove a proton from ethyne, HO− or -NH2?

a. For each of the acid–base reactions in [Section 2.3] <IMAGE>, compare the pKa values of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

(The pKa values you need are found in [Section 2.3] <IMAGE> or in [Problem 13] <IMAGE>)

1. <IMAGE>

2. <IMAGE>

a. For each of the acid–base reactions in [Section 2.3] <IMAGE>, compare the pKa values of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

(The pKa values you need are found in [Section 2.3] <IMAGE> or in [Problem 13] <IMAGE>)

3. <IMAGE>

4. <IMAGE>

Ethyne (HC≡CH) has a pKa value of 25, water has a pKa 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 data in Problem 47:

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?

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 <IMAGE]

j. CF3CH2O- + FCH2CH2OH

Complete the following acid–base reactions. In each case, indicate whether the equilibrium favors the reactants or the

products, and explain your reasoning.

(g) KOH + CH3CH2OH ⇌

Complete the following acid–base reactions. In each case, indicate whether the equilibrium favors the reactants or the

products, and explain your reasoning.

(f) (CH3)3C—O- + H2O ⇌

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 <IMAGE]

g. NaOCH2CH3 + Cl2CHCH2OH

h. H2Se + NaNH2

i. CH3CHFCOOH + FCH2CH2COO-

For each of the following compounds (here shown in their acidic forms), write the form that ­predominates in a solution with a pH=5.5:

c. H3O+ (pKa=−1.7)

d. HBr (pKa=−9)

Do the equilibria of the following acid–base reactions lie to the right or the left? (The pKa of H2O2 is 11.6.)

HOOH+HO−⇌HOO−+H2O

RC☰CH+HOO−⇌RC☰C−+HOOH

(•••) THINKING AHEAD Using pKₐ values for the conjugate acids of the bases on each side of the reaction arrow, identify which side of the equilibrium would be favored in the following hypothetical reactions.

(a) <IMAGE>

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 <IMAGE>] for any needed values of pKa, or estimate them. 

c. <IMAGE> + [CH3CH2SH2]+ —> <IMAGE> + CH3CH2SH 

d. NaNH2 + (CH3)3C—OH —> NH3 + (CH3)3C—ONa 

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 (pKa=4.9)

    2. CH3N+H3 (pKa=10.7)