- Chemicals :
Oxalic dehydrate acid crystal 1.58 g
KMnO4 solution 80 cm3
1 M dilute sulphuric acid 80 cm3
8. Apparatus and equipment :
- Procedure :
- 1.58 g of oxalic acid crystal was weighted accurately which was then dissolved in distilled water.
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The solution was transferred to volumetric flask and made up to 250 cm3 (the mark) by distilled water.
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25 cm3 of oxalic acid was pipetted in a conical flask. About 25 cm3 of 1 M dilute sulphuric acid was added to it so that the solution was acidified.
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The mixture was heated to about 60 oC by Bunsen burner.
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The hot mixture was titrated with KMnO4 solution until the colour changed form colourless to pink.
- Steps 3 to 5 were repeated for two more times.
- Observations :
The colour changed from colourless to pink at the end point.
- Data, Calculation and Results :
Volume of titrant = (20.20 + 20.15) / 2
= 20.175 cm3
Molar mass of oxalic dihydrate acid crystal
= 12 x 2 + 16 x 4 + 2 x 1 + 2(2 x 1 + 16)
= 126 g mol-1
No. of mole of oxalic dihydrate acid crystal = 1.58 / 126
= 0.0125397 mol
Molarity of the prepared oxalic dihydrate acid solution
= 0.0125397 / (250 x 10-3)
= 0.05 M
No. of mole of potassium permanganate solution
= No. of mole of 25 cm3 of oxalic dihydrate acid solution x 2/5
= 0.05 x 25 x 10-3 x 2/5
= 5 x 10-4 mol
Molar concentration of the given KMnO4 solution = 5 x 10-4 / 20.175 x 10-3
= 0.0248 M
12. Conclusion :
The molar concentration of the given KMnO4 solution was found to be 0.0248 M.
- Discussion :
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In this redox titration, no indicator is required as the end point can be determined by the colour change of reactant (KMnO4 solution).