Estimation of Ascorbic Acid

706 Words Apr 2nd, 2013 3 Pages
Title: Estimation of Ascorbic acid
Aim: To determine the ascorbic acid content of canned apple and orange juice To determine the volume of canned juice necessary to provide 75mg of Vitamin C

Introduction:
For the estimation of ascorbic acid, the method used involved the titration of the ascorbic acid, in the presence of a redox indicator 2,6-dichlorophenol-indophenol (DCPIP) which acts as both an oxidant so as to oxidise the ascorbic acid to dehydroascorbic acid, and it acts as an indicator to determine the end point of the titration. The samples of ascorbic acid used have to be made acidic first by adding metaphosphoric acid to remove proteins and ferric ions which would precipitate.

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52.60mL of apple juice solution contains 1.775 x 10-6 moles of acetic acid
1mL of apple juice solution contains 1.755 x 10-6/52.6 = 3.3 x 10-8 moles of acetic acid
Mass of 3.3 x 10-8 moles of ascorbic acid = 3.3 x 10-8 x 176g = 5.808 x 10-6g = 5.808 x 10-3 mg/mL
Volume of apple juice necessary to provide 75mg of vitamin C = (75/5.808 x 10-3) x 1000 = 12.9L

Discussion:
In this experiment the ascorbic acid content of canned orange juice and apple juice were determined via titrimetric analysis. The indicator used was 2,6-dichlorophenol-indophenol which also acts as an oxidising agent to oxidise the ascorbic acid. Since ascorbic acid is a potent reducing agent, it would become oxidised very quickly, so to reduce the chances of missing the end point of the titration, the samples used were diluted with distilled water.
Before the samples were titrated they were acidified with glacial acetic acid since they would be heavily diluted. Also 5% metaphosphoric acid was added to prevent the precipitation of proteins and ferric ions which would interfere with the end point of the titration. The results obtained show that it takes 8.5L of canned orange juice and 12.9L of canned apple juice to provide the
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