CHEM 220 – Buffers and Electrochemistry
1. (4 pts) Which of the following would you use to prepare a buffer with a pOH of 8?
a. trimethylamine
Ka = 1.59 x 10-10
b. pyridine
Kb = 3.3 x 10-8
c. hydrobromous acid Ka = 2.3 x 10-9
2. (6 pts) If your buffer’s pH is equal to 5.22 and it consists of 20.0mL of a 0.40N
diprotic acid, how much of an alkali metal salt of the conjugate base did you weigh out if
the molecular weight of this salt is 154 g/mol.
Ka = 4.90 x 10-5
3. (5 pts) What is the pH of your buffer if you are using 10.0mL of 0.200M butanoic acid (pKa
4.82) which contains 5.0 grams of the sodium salt of the conjugate base of this acid?
4.(10 pts)
Cr2O72-(aq) + U4+ (aq)
Cr3+ (aq) + UO22+ (aq); ACIDIC solution
a.(4 pts) Write the half reaction for the cathode?
b. (4 pts) Write the half reaction for the anode?
c. (2 pts) What species is the reducing agent in this oxidation reduction reaction?
5. (BONUS - +2 pts) Which one of these species would make the best oxidizing agent in a
redox reaction?
Eu3+ (aq) + 3e-
Eu(s)
E0 = -1.991 V
Au3+ (aq) + 2e-
Au+
E0 = +1.41 V
In3+ (aq) + 3e-
In (s)
E0 = -0.338 V
Li+ (aq) + e-
Li(s)
E0 = -3.040 V