1. With the aid of the pK_a table, determine the K_eq for each of the following reactions. Place an equilibrium arrow between the second and third structures that reflects the value of K_eq, i.e., Explain your results.

2. Determine the Gibbs free energy at 25 ^oC of the reaction NH₂^- + H⁺ -------> NH₃. Recall -ΔG^o = RT ln K_a (-ΔG^o = 2.3RT log K_a), where R = 1.98 cal/mole-^oK. The pK_a table will be of help.

The pK_a of ammonia is 35. But the reaction is run in reverse, thus the value is -35. pK_a equals -log K_eq. Under the conditions of the experiment 2.3RT = 1.38 kcal mol^{-1 o}K^-1. Therefore, ΔG^o = 1.38 pK_a. ΔG^o = 1.38 (-35) = -45 kcal/mol.

3. For each of the following mechanisms, illustrate the structures of the products. If a resonance structure applies, illustrate the resonance.

4. Phenol is converted to its anion by washing soda (Na₂CO₃) but not by baking soda (NaHCO₃). pKa's: H₂CO₃, 6.4; HCO₃^-, 10.3. Explain and illustrate. What is the value of K_eq for the reaction of phenol with the stronger of these two Brønsted base?

The pK_a of phenol is 10. It is slightly more acidic than bicarbonate. Carbonate is a slightly stronger base than phenoxide. The difference in pK_a's, 0.3, means that the equilibrium (antilog 0.3 = 2; K_eq = 2) favors bicarbonate and phenoxide. Carbonic acid is the strongest of the acids. Its conjugate base bicarbonate does not deprotonate phenol.

5. Using the curved arrow formalism, illustrate how the reactants in the following reactions are converted to products. You may have to redraw somes structures to show bonds and/or electron pairs. In each of the solutions notice that the atoms and charges on each side of the equation balance.