Name:___________________________________
AP
Chemistry
Date:_______________________________
Mr.Grodski III
Lab 9 – Oxidation-Reduction Titration
Introduction
Oxalate compounds have importance in many chemical and biological reactions. They are used in the
photographic sciences, and are the main component of kidney stones. Excess vitamin C is converted into
oxalate and excreted in the gut and urine, therefore, kidney stone patients must limit their intake of vitamin C
to control the formation of calcium oxalate stones, as well as foods high in oxalate, such as spinach, beets,
and beans.
Potassium permanganate reacts with oxalate ions to produce carbon dioxide and water in an acidic solution.
No indicators are necessary in permanganate titrations because the end point is easily observed. The
permanganate ion is intensely purple, whereas the manganese (II) ion is nearly colorless. The first slight
excess of permanganate imparts a pink color to the solution, signaling that all of the oxalate has been
consumed.
To determine the number of equivalents of H2C2O4 present in a sample, we need to know the exact
normality of the KMnO4 used in the titration, as well as the volume of the oxidizing agent used to reach the
endpoint. That is, we will need to standardize the KMnO4 solution first. The KMnO4 (of unknown
normality) is titrated against a known weight of pure ferrous ammonium sulfate [Fe(NH4)2 (SO4)2 • 6H2O],
a source of the Fe2+ ion. Once you have determined the normality of the KMnO4 solution you can use it as
the standard in your titration of H2C2O4 your unknown.
Materials
50 mL buret and clamp, beakers, thermometer, stirring rods, balance, hot plates, 0.02 M KMnO4, standard [Fe(NH4)2
(SO4)2 • 6H2O], ,H2C2O4 unknown, goggles.
Objectives:
1. To perform an oxidation – reduction titration.
2. To standardize a solution of KMnO4 with a known solution of [Fe(NH4)2 (SO4)2 • 6H2O].
3. To determine the concentration of oxalic acid (H2C2O4)
Reactions:
Standardization:
MnO4-(aq) + Fe+2(aq) → Mn+2(aq) + Fe+3
Unknown Titration:
MnO4-(aq) + H2C2O4(aq) → H2CO3 + Mn+2
Name:___________________________________
Standardization:
AP
Chemistry
Date:_______________________________
Mr.Grodski III
+2
MnO4 (aq) + Fe (aq) → Mn+2(aq) + Fe+3
Procedures and Analysis
I. Standardization of Permanganate Solution with Fe+2
1. Obtain 80 ml of the KMnO4 solution in a 100 ml beaker. Obtain 50 ml of the .100M Fe+2 solution in
another 100 ml beaker. Label both beakers.
2. Rinse the buret with approximately 10 ml of deionized water and then with two 5ml portions of the
3.
4.
5.
6.
7.
8.
MnO4- solution. Close the stopcock and fill buret to above the zero mark with MnO4- solution. Open
the stopcock to allow any air bubbles to escape from the tip. Close the stopcock when the liquid level
is between the 0- and 10-ml marks.
Record the initial volume of the solution to the nearest 0.01 of a ml.
Add 10 ml of the .100 M Fe+2 solution to a clean 250-ml erlymeyer flask with a volumetric pipet.
Record this volume.
Measure out 10 ml of the 6M H2SO4 into a clean 10ml graduated cylinder and add this to the
Erlenmeyer flask. Swirl to mix.
Titrate the Fe+2 solution with the MnO4- solution until the first trace of pink color persists for 30
seconds. Remember to swirl the flask and to rinse the walls of the flask with distilled water before
the endpoint is reached.
Record final buret reading as the final volume of the MnO- solution.
Repeat the standardization titration 2 more times.
Molarity of the MnO4-: ____________________
Name:___________________________________
Unknown Titration:
AP
Chemistry
Date:_______________________________
Mr.Grodski III
-
MnO4 (aq) + H2C2O4(aq) → H2CO3 + Mn+2
II. Determination of Oxalate in an Unknown Solution
1. Obtain 25 ml of the oxalic acid in a clean 250 ml beaker. Record the volume.
2. Add 5 drops of the 1.0 MnSO4 solution to the flask ( Mn+2 acts a catalyst)
3. Measure out and add 10 ml H2SO4 of 6M H2SO4 and add this to the flask.
4. Warm the flask to about 85◦C on the hot plate.
5. Immediately titrate this solution with the standardized MnO4- solution from part 1. Record both the
initial and final buret readings.
6. Repeat a second trial.
7. Balance all reactions.
8. Determine the concentration of the Oxalic Acid.