Chemistry 162 Name______
Show all work to receive maximum credit. Respect Significant Figures in Calculations.
1) (10 points) Answer questions a-h with reference to the two equations given below.
H2O (aq) + F- (aq) HF (aq) + OH- (l) Kb = 1.4 x 10-11
H2O (aq) + ClO2- (aq) HClO2 (aq) + OH- (l) Kb = 8.3 x 10-13
a) For 1 mole of each base dissolved separately in 1 liter of water, which base, F- or ClO2-, is the strongest?
b) Explain your choice in part a. Consider both qualitative (structural) and quantitative arguments.
c) For each base (not OH-) write the formula of its conjugate acid. ______
d) Write the formula of the most stable conjugate acid. ______
e) Explain your choice in part d, i.e. why is your choice most stable?
f) Are products or reactants favored in the following equilibrium? ______
HClO2 (aq) + F- (aq) HF (aq) + ClO2- (aq)
g) If fluoride, F-, is removed from the equilibrium mixture described by the equation in part f, what will happen? Explain. (The removal can be accomplished by adding Ca(NO3)2 to precipitate a CaF2.)
h) When the temperature of an aqueous solution of HF is increased Ka also increases.
i. Write the equilibrium equation for HF in aqueous solution.
ii Is the forward reaction exothermic or endothermic? Explain.
2) (2 points) Hydrogen iodide gas decomposes according to the following equilibrium reaction
HI(g) H2 (g) + I2 (g) Kp =5.93 x 10-7 at 30. °C.
Initially, if 1.0 mole each of H2, I2, and 2.0 mole of HI are placed in a 1.0 L container at 30. ºC.
Choose one outcome (a, b, c, d, or e) and explain your choice.
a) then to reach equilibrium the concentration of HI would decrease.
b) then the value of Kp would increase to 1.0.
c) then the total number of molecules would decrease.
d then the total number of molecules would increase.
e) then to reach equilibrium the concentration of H2 would decrease.
3) (10 points) Calculate the pH of a 0.050 M solution of pyridine. Pyridine (C5H5N) has a
pKb = 8.77. For full credit be sure to write the balanced equilibrium equation for reaction with water, set up an I.C.E. table and support your answer with a check.
4) (3 points)
(a) Equal moles of the following compounds are mixed together, HCO2H and NaC6H5O.
The acid’s Ka = 1.8 x 10-4 and base’s Kb = 9.9 x 10-5. The resulting salt solution is
a. basic. b. neutral. c. acidic. d. I need more information.
(b) A 0.01000 M solution of an electrolyte has a pOH = 2. The electrolyte is
a. a strong base b. a strong acid
c. a weak base d. a weak acid
e. neutral
(c) Which of the following solutions has the highest hydroxide-ion concentration?
a. 0.1 M HBr b. 0.001 M HNO3 c. pure water
d. a solution with pOH = 11 e. a solution with pH = 5
Extra Credit:
Choose the
a) strongest acid HN3 vs. HSCN
Explain your choice
b) weakest acid
Explain your choice