Ascorbic Acid Lab

Introduction:

Ascorbic acid is commonly known as vitamin C. Ascorbic acid is an antioxidant, meaning that it reacts readily with oxygen and losses its potency through exposure to light and heat. It is also water soluble so it leaches out of fruits and vegetables during cooking. Vitamin C is found in popular fruit drinks such as orange juice.

Titration is a procedure used for measuring the concentrations of substances in a solution.

Materials:

Ascorbic acid standard (20mg/100ml in 6% HPO 3 )
0.025 2,6-dichlorophenolindophenol solution dye
White grape juice, apple juice (any clear juice)
250 ml Erlenmeyer flask
50 ml Erlenmeyer flask

Procedure:

Standardized dye solution

  1. Place 5 ml of ascorbic acid solution into a 250 ml Erlenmeyer flask
  2. Add 5 ml of 6% HPO 3 to the ascorbic acid solution.
  3. Titrate with the 0.00625% 2,6-dichlorophenolindophenol dye solution until a light pink end point is reached and persists for 15 seconds.

    Calculation for standardization of the dye:

          T = 1/ml dye used

          T = the ascorbic acid equivalent of 1 ml of dye

Ascorbic acid determination :

  1. Obtain 10 ml of juice and place in a 50 ml Erlenmeyer flask.
  2. Add 10 ml of 6% HPO 3 to the Erlenmeyer flask.
  3. Titrate with the 0.00625% 2,6-dichlorophenolindophenol dye until a light pink end point is reached and is persistent for 15 seconds. Make sure to record the number of ml of dye that is added.

          Calculations:
         ((V)(T) / W) x 100 = mg ascorbic acid/5 g sample

    V = ml dye used to reach pink end point
    T = Ascorbic acid equivalent of dye solution expressed as mg/ml of dye
    W = mass of juice (5g)

    W = 10ml sample / 20 ml total volume X 10ml used to titrate = 5g

Reference:

Burns, E.E. "Laboratory Manual for FSTC/HORT 311 - Principles in Food Processing." Texas A&M University. College Station, TX.

Questions:

  1. What was the amount of ascorbic acid in the fruit drink(s) you tested? Make sure you show your calculations!



  2. Among the beverages tested, were any unexpectedly low or high? If so, which beverage and what did you expect the amount of vitamin C to be?



  3. Check the label of the fruit drink and compare the amount of vitamin C that is stated on the label to the calculations that you obtained. Is there a difference? If so, how can you account for the difference?



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