Redox Titration: Permanganate against Oxalate (Ethanedioate)
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Redox Titration: Permanganate against Oxalate (Ethanedioate) Aims: Find out the concentration of oxalic acid and oxalate by titration with sodium hydroxide. Chemical: Mixture of oxalic acid and oxalate, standard NaOH(about 0.05M), standard KMnO4(about 0.02M), 2M H2SO4, phenolphthalein indicator Apparatus: Titration apparatus, Bunsen burner Procedure: (A) Dilution The mixture of oxalic acid and oxalate should be diluted ten times. Using pipette filler pipette 25cm3 of given solution and dilute it to 250cm3 in a volumetric flask. The resulting solution can be used for subsequent titration. (B) Acid-base titration Titrate a 25cm3 portion of the diluted mixture against the given standard Sodium Hydroxide (0.05M).
Further heating is necessary during the titration as the mixture is cooled down. Repeat the titration at least twice. Data: (A) Morality of standard sodium hydroxide solution: 0.05M Titration volume (cm3) Trial 1 2 3 Final burette reading 4.00 7.50 10.95 14.50 Initial burette reading 035 4.00 7.50 10.95 Volume of NaOH used 3.65 3.50 3.45 3.55 (B) Morality of standard potassium permanganate solution: 0.02M Titration volume (cm3) Trial 1 2 3 Final burette reading 8.70 11.95 15.10 18.25 Initial burette reading 5.10 8.70 11.95 15.10 Volume of NaOH used 3.60 3.25 3.15 3.15 Calculation: (1)
original mixture is 0.0636M Discussion: We can also use the methyl orange, as the indicator because it also has a clear colour change during the titration .It will change to the yellow when it is in the acid condition. When it turns to alkali, it will turn to colourless. During the titration, if the temperature is below 70 C the reaction will very slow. It is because the optimum temperature of reaction is 70 C, when it reachs70 C the reaction become very effective. We cannot determine the concentration by weighting and dissolving in water because there are some impurities occurs. During the process, the solid is not 100% dissolve in the water and may polluted.
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