Estimation of the Vitamin-C content in tablet.

 

Aim

To estimate the amount of Vitamin C (ascorbic acid) present in the given tablet/sample by titration with standard dye solution (2,6–Dichlorophenol Indophenol).

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Principle

Vitamin C (ascorbic acid) is a strong reducing agent. It reduces the blue dye 2,6–Dichlorophenol Indophenol (DCPIP) to a colorless form in acidic medium.

During titration, the dye is reduced by Vitamin C until all the Vitamin C is consumed. The appearance of a permanent light pink colour indicates the end point.

Reaction (simplified):

Ascorbic acid + DCPIP (blue) → Dehydroascorbic acid + DCPIP (colorless)

Thus, the amount of dye consumed is proportional to the amount of Vitamin C present in the sample.

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Apparatus

• Burette

• Pipette

• Conical flask

• Volumetric flask

• Funnel

• Beaker

• Filter paper

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Chemicals / Reagents

• Vitamin C tablet/sample solution

• Standard DCPIP dye solution

• Oxalic acid solution (4%)

• Distilled water

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Procedure

1. Preparation of Standard Vitamin C Solution

1. Weigh accurately 100 mg of pure ascorbic acid.

2. Dissolve it in 100 ml of 4% oxalic acid solution in a volumetric flask.

3. This gives a standard Vitamin C solution.

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2. Standardization of Dye Solution

1. Pipette 10 ml of standard Vitamin C solution into a conical flask.

2. Titrate it with DCPIP dye solution taken in the burette.

3. Continue titration until a light pink colour persists for about 15 seconds.

4. Note the burette reading.

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3. Preparation of Sample Solution

1. Weigh the Vitamin C tablet and crush it into powder.

2. Dissolve a known amount of the powder in 100 ml of 4% oxalic acid solution.

3. Filter the solution to remove insoluble materials.

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4. Titration of Sample

1. Pipette 10 ml of the sample solution into a conical flask.

2. Titrate with standard DCPIP dye solution until a permanent light pink colour appears.

3. Record the burette reading.

   Observations

   1. Standardization of Dye (DCPIP)

   Sr. No.	Volume of Standard Vitamin C solution (ml)	Initial Burette Reading (ml)	Final Burette Reading (ml)	Volume of Dye Used (ml)
   1	10
   2	10
   3	10

   Average volume of dye used = ______ ml

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   2. Estimation of Vitamin C in Sample

   Sr. No.	Volume of Sample Solution (ml)	Initial Burette Reading (ml)	Final Burette Reading (ml)	Volume of Dye Used (ml)
   1	10
   2	10
   3	10

   Average volume of dye used for sample = ______ ml

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   Calculations

   Let

   • $V_1$ = Volume of dye used for standard Vitamin C solution (ml)

   • $V_2$ = Volume of dye used for sample solution (ml)

   • $W$ = Weight of sample taken (mg)

   Amount of Vitamin C in sample is calculated using:

   $$\text{Vitamin C (mg)} = \frac{V_2}{V_1} \times \text{Amount of standard Vitamin C}$$

   If 10 ml standard solution contains 1 mg Vitamin C, then

   $$\text{Vitamin C in sample} = \frac{V_2}{V_1} \times 1 \text{ mg}$$

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   Percentage of Vitamin C

   $$\text{Percentage of Vitamin C} = \frac{\text{Amount of Vitamin C found}}{\text{Weight of sample}} \times 100$$

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   Example format for record:

   Amount of Vitamin C in the given sample = _____ mg

   Percentage of Vitamin C = _____ %

   Result

   The amount of Vitamin C present in the given tablet/sample is calculated from the titration values and expressed in mg or percentage.

   Example:
   Vitamin C content in the given sample = _____ mg per tablet (or per sample).