Buffers – CHEM 220 – March 17 and 19– In-class WS
1. Which of the following would you use to prepare a buffer with a pH of 4.6
a. aminobenzene
Kb = 3.98 x 10-10
b. ammonia
Ka = 5.69 x 10-10
c. 1-naphthol
Ka = 3.84 x 10-10
2. A buffer was prepared by dissolving 0.100 moles of a weak acid (Ka equal to 1.00 x 10-5 )
plus 0.050 mol of its conjugate base in 1.00L.
a. What is the pH of this buffer?
b. Does your answer in “part a” make sense? Explain.
3. You are supposed to make a buffer from HNO2 and a salt of its conjugate base. If the Ka for
HNO2 is 7.08 x 10-4 and you want a buffer with a pH equal to 5.00, what mole ratio of acid to
conjugate base do you need in your buffer solution?
4. You were asked by your Biochemistry professor to make a buffer with a pH equal to 3.50.
You decide that you will dissolve the conjugate base in 2.00L of 2M weak acid. How many
moles of conjugate base do you need to dissolve in the weak acid?
Acids to choose from
1. citric acid
2. hypochlorous acid
3. nitrous acid
Ka1 = 7.45 x 10-4
Ka = 3.0 x 10-8
Ka = 7.1 x 10-4