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O-4
In this experiment we will introduce you to a new procedure called “pipetting”. Pipetting involves the
accurate transfer of a known volume of solution and is often used in quantitative titrations. Your
laboratory instructor will demonstrate the correct use of a pipet.
EXPERIMENTAL METHOD
In Part I, you will standardize a potassium permanganate solution that was prepared in advance and
allowed to stabilize. Prior to using, this solution was filtered to remove any MnO2 impurity. To
standardize the solution, you will prepare a solution of the primary standard oxalic acid dihydrate. Once
the potassium permanganate has been standardized, you will use this solution in Part II to determine the
concentration of hydrogen peroxide in an unknown sample.
ADVANCE STUDY ASSIGNMENT
1.
Calculate the mass of oxalic acid dihydrate that is required to prepare 100.0 mL of a solution that is
0.1000 M oxalic acid.
Answer: 1.261 g
2.
Give the overall balanced equation and the expected E
cell
for the redox reaction between oxalic
acid and potassium permanganate.
Answer:
2 MnO
4
-
(aq)
+ 6H
+
(aq)
+ 5 H2C2O
4(aq)
2 Mn
2+
(aq)
+ 8 H2O
(l)
+ 10 CO
2(g)
E
cell
= 1.997 V
3.
A 20.00 mL sample of 0.09873 M oxalic acid was titrated with potassium permanganate. If 32.33
mL of a KMnO
4
solution was required to reach the pink end point, what molarity of the KMnO
4
solution should be reported?
Answer: 0.02443 M
4.
A 20.17 mL sample of an unknown containing hydrogen peroxide was titrated with the standardized
KMnO
4
solution described in question 3. The pink end point was reached after the addition of
42.74 mL of KMnO
4
. What is the hydrogen peroxide concentration in the unknown sample? Answer: 0.1294 M
5.
What is the purpose of using sulfuric acid in this experiment?
Answer: Reaction solution must be acidic
6.
Why can’t we use hydrochloric acid or nitric acid to acidify the solutions?
Answer: Cl
-
will react with the permanganate ion and hydrogen peroxide while NO3
-
will react with oxalic acid and h
