(a) To prepare 100ml of M/40 solution of oxalic acid.
(b)Using this calculate the molarity and strength of the given KMnO4 solution.
APPARATUS AND CHEMICALS REQUIRED–
Oxalic acid, weighing bottle, weight box, volumetric flask, funnel, distilled water, chemical balance, beakers, conical flask, funnel, burette, pipette, clamp stand, tile, dilute H2SO4, KMnO4 solution.
Oxalic acid is a dicarboxylic acid having molar mass 126gmol-1. It is a primary standard and has the molecular formula COOH-COOH.2H2O. Its equivalent mass is 126/2 = 63 as its n factor is 2 as per the following reaction:
COOH-COOH → 2CO2 + 2H+ + 2e–.
- Weigh a clean dry bottle using a chemical balance.
- Add 3.15g more weights to the pan containing the weights for the weighing bottle.
- Add oxalic acid in small amounts to the weighing bottle, so that the pans are balanced.
- Remove the weighing bottle from the pan.
- Using a funnel, transfer the oxalic acid to the volumetric flask.
- Add a few drops of distilled water to dissolve the oxalic acid.
- Make up the volume to the required level using distilled water.
- The standard solution is prepared.
- The reaction between KMnO4 and oxalic acid is a redox reaction and the titration is therefore called a redox titration.
- Oxalic acid is the reducing agent and KMnO4 is the oxidizing agent.
- KMnO4 acts as an oxidizing agent in all the mediums; i.e. acidic, basic and neutral medium.
- KMnO4 acts as the strongest oxidizing agent in the acidic medium and therefore dil. H2SO4 is added to the conical flask before starting the titration.
- The titration between oxalic acid and KMnO4 is a slow reaction, therefore heat the oxalic acid solution to about 600C to increase the rate of the reaction.
IONIC EQUATIONS INVOLVED:
Reduction Half: MnO4– + 8H+ + 5e– → Mn2+ + 4H2O] X 2
Oxidation Half: C2O42- → 2CO2 + 2e– ] X 5
Overall Equation: 2MnO4– + 16H+ + 5C2O42- → 2Mn2+ + 10CO2 + H2O
INDICATOR– KMnO4 acts as a self indicator.
END POINT– Colourless to light pink (KMnO4 in the burette)
1. Fill the burette with KMnO4 solution.
2. Pipette out 10ml. of oxalic acid solution into the conical flask.
3. Add half a test tube of dil. H2SO4 and heat the solution to about 600C to increase the rate of the reaction.
4. Keep a glazed tile under the burette and place the conical flask on it.
5. Note down the initial reading of the burette.
6. Run down the KMnO4 solution into the conical flask dropwise with shaking.
7. Stop the titration when a permanent pink colour is obtained in the solution.
8. This is the endpoint. Note down the final burette reading.
9. Repeat the experiment until three concordant values are obtained.
OBSERVATION TABLE: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL)
Volume of Oxalic Acid solution taken = 10mL
||Volume of KMnO4
Concordant Value = 10.5mL
CALCULATIONS: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL)
Calculation of amount of oxalic acid to be weighed to prepare 100ml M/20 solution:
Molecular Mass of Oxalic Acid = 126g/mole
1000 cm3 of 1M oxalic acid require 126g oxalic acid.
1000 cm3 of M/40 oxalic acid require =126/40g = 3.15g
N1M1V1 = N2M2V2
Where N1=5 (for KMnO4), V1= 10.5 , M1 = ?
N2=2 (for oxalic acid), V2 = 10ml, M2 = 1/40
M1 = [2*(1/40)*10]/[5*10.5] = 1/105M = 0.0095M
Strength = M X Molar Mass = 158 *( 1/105) = 1.504g/L
RESULT- (ON RULED SIDE)–
The Molarity of KMnO4 = 0.0095M
And the strength of KMnO4 = 1.504g/L
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