Titrant (in burette): Potassium Dichromate
Titrate (in conical flask): 25.0cm3 of Fe2+ Solution
Indicator used: N-phenylanthranilic acid indicator
Colour of indicator changed from: Orange to Purple
Average volume: 24.20 cm3
Calculation:
Number of mole of Kr2Cr2O7 = 1.2430 / [(7)(15.9994)+(2)(51.9961)+(2)(39.0983)]
= 0.004225
∵ Cr2O72- : Fe2+ = 1 : 6
∴ Number of mole of Fe2+ = [(0.004225)(6)](25/250)
= 0.002535
Molarity of Fe2+ = 0.0002535 / (24.2/1000)
= 0.1047
~ 0.10M
Titration I: Standardization of iron(II) solution (continued)
Titrant (in burette): Potassium Dichromate Solution
Titrate (in Conical flask): 25.0cm3 of Fe2+ Solution
Indicator used: Barium diphenylamine sulphonate indicator
Colour of indicator changed from: Colourless to Violet
Average volume: 24.23 cm3
Calculation:
∵ due to last titration I’s calculation
∴Number of mole of Fe2+ = 0.002535
Molarity of Fe2+ solution = 0.002535 / (24.23/1000)
= 0.1046
~ 0.10M
Titration II: Determination of the potassium permanganate solution
Titrant (in burette): Potassium Permanganate Solution
Titrate (in Conical flask): 25.0cm3 of Fe2+ Solution
Indicator used: Potassium Permanganate Solution
Colour of indicator changed from: Green to Pink
Average volume: 24.63 cm3
Calculation:
Number of mole of Fe2+ = (0.1046)(25.0/1000)
= 0.002615
∵ KMnO4 : Fe2+ = 1 : 5
∴ Number of mole of KMnO4 = 0.002615 / 5
= 0.000523
Molarity of KMnO4 = 0.013075 / (24.63/1000)
= 0.02123
~ 0.02M
Titration III: Estimation of the concentration of hydrogen peroxide solution
Titrant (in burette): Potassium Permanganate Solution
Titrate (in Conical flask): 25.0cm3 of Hydrogen Peroxide Solution
Indicator used: Potassium Permanganate Solution
Colour of indicator changed from: Colourless to Pink
Average volume: 21.23 cm3
Calculation:
Number of mole of KMnO4 = (0.02123)(21.23/1000)
= 0.000450712
∵ KMnO4 : H2O2 = 2 : 5
∴ Number of mole of H2O2(dil) = (0.000450712)(5 / 2)
= 0.0011268
Molarity of H2O2(dil) = 0.0011268 / (25/1000)
= 0.045072
~ 0.045M
Molarity of H2O2 = (0.045072)(250/5)
= 2.2536
~ 2.25M
Number of mole of H2O2 = (2.2536)(5/1000)
= 0.011268
Mass of H2O2 = [(2)(1.00794)+(2)(15.9994)](0.011268)
= (34.01468)(0.011268)
= 0.38328
Percentage of H2O2 = (0.38328 / 5) (100%)
= 7.6656
~ 7.67%
Volume concentration of H2O2 = (7.67/6.8)(22.4)
= 25.26588 volume
~ 25.27 volume
Discussion:
- Deep colour of potassium permanganate solution will show out two meniscuses but according to burette using, we are try to measure the volume by different. Therefore if we technically use the same meniscuses in the all reading, it will be fine for the experiment.
- Store the dilute hydrogen peroxide in a cool, dry and well-ventilated area. Also put it in a steel or glass and opaque container. On the other hand, keep away from heat, flame and light.
Conclusion:
In titration I, we standardize the iron(II) solution is 0.10M with N-phenylanthranilic acid indicator and Barium diphenylamine sulphonate indicator.
In titration II, we determined the potassium permanganate solution is 0.02M.
In titration III, we estimated the dilute hydrogen peroxide is 0.038g and we found out the molarity of it is 0.045M. And for the original hydrogen peroxide’s percentage is 7.67%(w/v) and volume concentration is 25.27 volume.