(19) Ammonium formate, NH4(HCOO), dissolves in water to giveammonium ions and formate ions. These ions then undergo anunfavorable and endothermic Brønsted acid- base reaction accordingto this equation:
NH4+ (aq) + HCOO– (aq) NH3 (aq) +HCOOH (aq)
Keq < 1 (at 298 K)
∆Horxn > 0
(a) (8 pts.) Calculate Keq and∆Gorxn (at 298 K) for equation (19).
(b) (6 pts.) Qualitatively, would one expect∆Sorxn for equation (19) to be positive ornegative? Briefly justify your answer.
(c) (10 pts.) If 1.00 mol NH4(HCOO) is dissolved in 1.00 L waterat 298 K, what is the pH of the solution?
(d) (7 pts.) The solution from part (c) (1.00 mol NH4(HCOO) in1.00 L water) can be made into an effective buffer at pH =3.00 by the addition of either NaOH or HCl. Specifywhether NaOH or HCl would be required, and whether more than 0.500or less than 0.500 mol of the reagent would be needed.
(e) (8 pts.) Consider the solution from part (c) (1.00 molNH4(HCOO) in 1.00 L water at 298 K). For each of the changes below,circle the effect on the concentration of NH3 (aq) atequilibrium after the change is made, and briefly give thereasoning for your choice.
NH4+ (aq) + HCOO– (aq) NH3 (aq) +HCOOH (aq)
Keq < 1 (at 298 K)
∆Horxn > 0
(i) The temperature of the solution is increased to 340 K.
[NH3] increases[NH3] decreases[NH3] does notchange
Explanation:
(ii) The volume of the solution is increased to 2.00 L by adding1.00 L water.
[NH3] increases[NH3] decreases[NH3] does notchange
Explanation:
