1. Name _________________________
Testing for Vitamin C content
Introduction
One of the main selling points for different brands of orange juice are he
benefits gained from a high Vitamin C content. How strict are the standards regulating
the advertised vitamin and mineral content of foods? How accurate is the packaging
information for a number of different brands of orange juice? A useful tool in trying
to answer these questions is indophenol solution, an indicator that turs clear when
neutralized by an equal amount of ascorbic acid (pure vitamin C).
Materials
Indophenol solution 0.1% ascorbic acid
6 test tubes 0.05% ascorbic acid
Droppers Juicer
Funnel An orange
Filter paper 4 different brands of orange juice
Beaker
Method
TASK 1
• Place 15 drops of indophenol solution in a test tube
• Add the 0.1% ascorbic acid solution one drop at a time, to the indophenol
solution, counting each drop and swirling the test tube after each one
• Continue until the indophenol becomes colourless
• Record the number of drops required
• Repeat twice more and then another 3 times with the 0.05% ascorbic acid
TASK 2
• Place the funnel over a small beaker and lay the filter paper across the mouth
of the funnel
• Squeeze the juice from half an orange and slowly and carefully strain it
through the funnel
• Perform the same steps as in task 1, but this time using fresh orange juice in
the place of ascorbic acid.
• Repeat twice more to verify result
• Based on the number of drops required, calculate as accurately as possible the
ascorbic acid content of orange juice. Show all calculations
TASK 3
• Filter a sample of orange juice through the filter paper and funnel

2. • Repeat the process as per task 1, performing a total of 3 repetitions
• Record the number of drops required and calculate the ascorbic acid content of
this juice sample.
• Refer to the label on the bottle, what claims does it make with regard to %
content of real orange juice, can you verify or deny these claims?
• Refer to the label for the Vitamin C content and use this to calculate the
concentration, working on the assumption that 1g per ml = 100%.
• Repeat for 3 other juice samples
Results
TASK 1
Number of drops required
Trial #1 Trial #2 Trial #3 Average
0.1% Ascorbic acid
0.05% Ascorbic acid
TASK 2
Number of drops required
Trial #1 Trial #2 Trial #3 Average
Fresh orange juice
Calculate % vol of ascorbic acid in orange juice
Formula No. of drops of ascorbic acid = x
No. of drops of orange juice = %vol of AA
Eg 20 = x
50 = 0.1
2/5 = x/0.1
x = 2/5 * 1/10
x = 3/50
x = 0.06
Calculations

3. TASK 3
Number of drops required
Trial #1 Trial #2 Trial #3 Average
Calculate % vol of all 4 samples
Discussion questions
Q1. On the supplied graph paper draw a bar graph to display a side-by-side
comparison of all 5 samples of orange juice tested. Record the concentration on
the y axis.
For the 4 commercial brands of orange juice, display a second bar indicating the
claimed concentration of ascorbic acid,
Q2. How did each of the 4 commercial brands compare with regard to claimed
and actual vitamin C content?

4. Q3. For any of the commercial brands that state the % of the drink that is actual
orange juice, using vitamin C concentration as a basis for comparison, calculate
and comment on the validity of these claims.
Q4, What may account for any of the differences observed in your answer to
question 3?
Q5. The recommended daily intake of vitamin C ranges from 45mg to 100mg,
depending on the nutritionist with which you speak. How easily can this
requirement be met with the tested products?
Q6. Some radical proponents of an alternative health movement advocate
‘megadosing’ and advise a daily intake of 2000mg. Would you recommend any of
the tested products for this purpose? Explain your answer.