Determination of the Molarity of a Permanganate Solution Via Titration

Purpose:

The purpose of this experiment is to determine the molarity of a permanganate solution through the use of redox titration.

Theory:

The following are the reactions that take place in the experiment:

Unbalanced: H2C2 O4 (aq) + MnO4- (aq)  CO2 (g) + Mn2+(aq)

H2C2 O4 Half-Reaction: H2C2 O4 (aq)  2CO2 (g) + 2e- + 2H+(aq)

MnO4- Half-Reaction: 8H+ + 2MnO4-(aq) + 5e-  Mn2+(aq) + 4H20 (l)

Net Reaction: 5H2C2 O4 (aq) + 6H+ + 2MnO4- (aq)  10CO2 (g) + 2 Mn2+(aq) +8H20 (l)

The solution was heated in order to reach better reaction rates, since the reaction occurs slowly at room temperature. Unlike many other titrations no indicator is necessary to tell the experimenter when the endpoint of the reaction is. In this case, the experimenter knows when all the oxalate has been consumed because the excess of permanganate will show up as a pink color. Thus, the permanganate ion acts as an indicator itself. The reaction produces its own catalyst in the form of Mn2+ that promotes oxidation. The sulfuric acid added to the titration flask acts as a proton donor for the solution readily giving up protons. Since the oxalic acid is not a strong acid and does not dissociate well, but is still needed in the reaction to form carbon dioxide, the addition of a strong acid, sulfuric acid, supplies the protons needed for the reaction.

Procedure:

Obtain and zero two burets, one containing .0500M oxalic acid and the other containing the permanganate solution. Next, add 25.00mL of the oxalic acid into a 250mL Erlenmeyer flask (using the bottom of the meniscus for measurements). Then proceed to measure and add 15mL of 3M sulfuric acid to the titration flask with a graduated cylinder. Heat the titration flask to a temperature of 80C. Titrate the contents of the flask with the permanganate solution. Swirl the contents of the flask after adding the permanganate and if the solution drops below 80C heat the flask back up to 80C. Use the top of the permanganate solution to take measurements rather than the bottom of the meniscus. Add just enough permanganate to turn the contents of the flask a light pink color. At this point record the volume of the permanganate solution used. Rinse the titration flask with distilled water and run the experiment one more time.

Data:

Quantitative:

(Trial One):

1. Volume of .0500M Oxalic Acid (H2C2 O4 (aq)) 25.00mL

2. Volume of Permanganate Solution (MnO4- (aq)) 24.55mL

3. Volume of Sulfuric Acid (H2SO4 (aq)) 15.00mL

(Trial Two):

1. Volume of .0500M Oxalic Acid (H2C2 O4 (aq)) 25.00mL

2. Volume of Permanganate Solution (MnO4- (aq)) 24.06mL

3. Volume of Sulfuric Acid (H2SO4 (aq)) 15.00mL

Qualitative:

The sulfuric acid and the oxalic acid are both clear in color, while the permanganate solution is a dark purple color. At first, when the permanganate is added to the titration flask containing both oxalic and sulfuric acid the solution within the flask turns a pink color and suddenly disappears, until the endpoint is reached. The endpoint is when one drop of the permanganate solution changes the color of the titration flask to a slight pink color for more than fifteen seconds.

Calculations:

Balanced Net Reaction:

5H2C2 O4 (aq) + 6H+ + 2MnO4- (aq)  10CO2 (g) + 2 Mn2+(aq)