lab # 2: Estimation of Ascorbic acid

This lab involved two major parts: (1)Standardization and (2)the Estimation of Ascorbic Acid in canned juice.
In part one the ascorbic acid was placed in a burette and 20 ml of dichlorphenol-indophenol (DCPIP) solution was pipetted into an Erlenmeyer flask. Then the DCPIP was titrated with the ascorbic acid until a colour change of pink to colourless was observed. This took approximately 30 – 120 seconds to occur so great attention was needed to avoid overshooting during the this titration.
For part two there was two kind of juice to be titrated; orange and apple. In each bench the students were divided into groups, before the lab. Each group did part one and used only one of the juice for part two. Then the demonstrator made apple and orange stock: He/she poured 2ml of the canned juice (orange/apple) into 500ml beaker and acidified it with 0.2ml of glacial acetic acid. The volume was made up to 50ml with distilled water and mixed thoroughly. The rest was done by the students.
25ml of the stock made was transferred to a 50ml conical flask, using a measuring cylinder. 2oml of 5% metaphosphoric acid was added and the volume made up to 50ml by adding 5ml of distilled water. This solution was then transferred to a burette and approximately three 5ml volumes of DCPIP was titrated until a colour change of pink to colourless was observed. This titration took a longer time and as such large quantities of the juice preparation was used for each titration.

By Amethyst

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