vitamin c prac

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 acid6 test tubes 0.05% ascorbic acidDroppers JuicerFunnel An orangeFilter 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 calculationsTASK 3

Filter a sample of orange juice through the filter paper and funnel

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 requiredTrial #1 Trial #2 Trial #3 Average

0.1% Ascorbic acid0.05% Ascorbic acid

TASK 2


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 = x50 = 0.1

2/5 = x/0.1

x = 2/5 * 1/10

x = 3/50

x = 0.06

Calculations

TASK 3


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?

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.

vitamin c prac

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