CHEM
55 Quantitative Analysis Lab
Page 1 of 3
Homework for Phosphate Analysis
Name __________________________
1. Give directions for preparing 250 mL of about 0.1M NaOH solution from
50% w/v NaOH. Assume that the specific gravity of 50% NaOH is 1.48 g
cm-3.
2. If sodium carbonate were to be a contaminant in the NaOH solution
above, how would it degrade the quality of the solution as a standard base
for titration?
CHEM
55 Quantitative Analysis Lab
Page 2 of 3
Homework for Phosphate Analysis
3. Sketch a hypothetical titration curve for the titration of 50 mL of 0.055M
acetic acid (look up the pKa) with 0.103M NaOH. Indicate the important
pH and volume points (equivalence and pK values) on the graph.
12
10
pH
8
6
4
2
0
0
5
10
15
20
25
Volume NaOH added / mL
30
35
CHEM
55 Quantitative Analysis Lab
Page 3 of 3
Homework for Phosphate Analysis
4. A 50.0 mL a mixture of H3PO4 and NaH2PO4 is titrated with 0.1100 M
NaOH. The first end point occurs at 10.23 mL, and the second end point
occurs at 35.25 mL.
a. What is the molarity of the H3PO4?
b. What is the molarity of the NaH2PO4?
c. What is the w/v % H3PO4?
d. What is the w/v % NaH2PO4?
e. Calculate the initial pH to three figures (x.xx) given the following:
K1 = 7.11x10-3, K2 = 6.34x10-8, K3 = 4.2x10-13. Activity need not
be considered.