CHEM
55 Quantitative Analysis Lab
Page 1 of 2
Homework for Phosphate Analysis
Name __________________________
1. Sketch a hypothetical titration curve for the titration of 50 mL of 0.0 125 M
phosphoric acid (H3PO4) (K1 = 7.11x10-3, K2 = 6.34x10-8, K3 = 4.2x10-13)
with 0.103M NaOH. The fictitious titration should cross through all three
equivalences (i.e. it should progress through the fully basic form). Indicate
on the graph the solution pH at a. the first and b. the second equivalence
points and the two half-equivalence points (i.e. c. the points midway
between zero and the first and d. midway between the first and second
equivalence points). Finally, indicate the three (e, f, g) equivalence
volumes on the graph.
H3PO4 Titration
14.0
13.0
12.0
11.0
10.0
9.0
pH
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
5
10
15
20
NaOH added / mL
25
30
35
40
CHEM
55 Quantitative Analysis Lab
Page 2 of 2
Homework for Phosphate Analysis
2. A 50.00 mL a mixture of H3PO4 and NaH2PO4 is titrated with
0.1050 M NaOH. The first end point occurs at 5.07 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?
Atom AW
g.mol-1
______________
C
12.010
H
1.007
N
14.01
O
16.00
P
30.974
Na
22.990
Al
26.98
Mn
54.94
Br
79.90
Cl
35.54