AP Chemistry
WS 11.4
30. A liter of benzoic acid (HBen) and sodium benzoate (Ben-) buffer is prepared using 1.00 mol of benzoic acid and 0.50 mol of
sodium benzoate. The Ka for HBen is 6.3 x 10-5.
a. If 0.100 mol of H+ is added. Calculate the following:
mol HBen
mol Ben-
[H+]E
pH
b.
0.100 mol of OH- is added. Calculate
mol HBen
mol Ben-
[H+]E
pH
31. A buffer is prepared by adding 2.00 mol of HC2H3O2 and 2.00 mol of NaC2H3O2 to enough water to make 5.00 L of solution.
Acetic acid has a Ka = 1.8 x 10-5. Calculate
a. the pH of the buffer.
b.
the pH when 0.50 mol of H+ is added.
mol HC2H3O2
mol C2H3O2-
[H+]E
pH
c.
the pH when 0.50 mol of OH- is added.
mol HC2H3O2
mol C2H3O2-
[H+]E
pH
32. Calculate the pH of 0.500 L of a buffer solution composed of 0.50 M formic acid and 0.70 M sodium formate before and after
adding 10.0 mL of 1.00 M HCl.
33. Choose an acid from the Ka tables in the appendix of your book and an appropriate salt and design a buffer that has a pH of
5.00. Calculate the concentrations of the acid and it’s complimentary salt.
34. What could you mix with 100.0 mL of 2.00 M HNO2 (nitrous acid) to make a buffer? What is the pH of the most effective buffer
made from nitrous acid, HNO2? Ka of HNO2 = 4.0 x 10 .
35. The weak acid, HCN, could be used to make a buffer. The Ka for HCN is 6.2 x 10 .
a) What is the pH of an effective buffer made from HCN?
b) What ratio of [HCN] to [CN ] is needed to have a buffer with pH = 9.00?
35. Which of the following mixtures would result in a buffer
solution?
I. 10 mL 0.20 M HCl and 10 mL 0.40 M NH3
II. 10 mL 0.20 M HF and 10 mL 0.20 M NaF
III. 10 mL 0.40 M HC2H3O2 and 10 mL 0.20 M NaOH
A)
B)
C)
D)
E)
II only
II and III only
I and III only
I, II and III
None of these will result in a buffer
solution.