Estimation of Ascorbic Acid

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  • Topic: Vitamin C, Ascorbic acid, Vinegar
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  • Published : March 18, 2013
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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.

*This diagram was located on the website: http://faculty.mckendree.edu/scholars/winter2007/gummersheimer.htm

Results:
Table 1: Standardization of 2,6-dichlorophenol-indophenol
Titration #| 1| 2| 3|
Initial Volume (mL)| 45.20| 47.50| 49.10|
Final Volume( mL)| 47.50| 49.10| 50.00|
Volume used (mL)| 5.30| 1.60| 0.90|
Mean ± standard deviation: 1.25 ± 0.7

Table 2: Titration with Canned orange juice
Titration #| 1| 2| 3|
Initial Volume (mL)| 5.20| 4.40| 5.50|
Final Volume( mL)| 40.30| 39.40| 40.60|
Volume used (mL)| 35.10| 35.00| 35.10|
Mean: 35.07mL
Table 3: Titration with Canned apple juice
Titration #| 1| 2| 3|
Initial Volume (mL)| 0.00| 0.00| 0.00|
Final Volume( mL)| 53.20| 55.00| 49.60|
Volume used (mL)| 53.20| 55.00| 49.60|
Mean: 52.60mL

Molar mass of ascorbic acid = 176mg,mass of ascorbic acid used = 1.25mg Number of moles in 0.00125g of ascorbic acid = 1/176 x 0.00125 = 7.102 x 10-6 moles Mole ratio of DCPIP: Ascorbic acid = 1:1

Number of moles of DCPIP used = 7.102 x 10-6 moles

If 20mL of DCPIP = 7.102 x 10-6 moles
Then 1 mL of DCPIP = 7.102 x 10-6/20 = 3.55 x 10-7 moles
Therefore 5 mL of DCPIP = 3.55 x 10-7 x 5 = 1.775 x 10-6 moles

Since mole ratio of DCPIP: Ascorbic acid...
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