Vitamin C prac


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Vitamin C prac

  1. 1. Name _________________________ Testing for Vitamin C contentIntroduction One of the main selling points for different brands of orange juice are hebenefits gained from a high Vitamin C content. How strict are the standards regulatingthe advertised vitamin and mineral content of foods? How accurate is the packaginginformation for a number of different brands of orange juice? A useful tool in tryingto answer these questions is indophenol solution, an indicator that turs clear whenneutralized by an equal amount of ascorbic acid (pure vitamin C).MaterialsIndophenol solution 0.1% ascorbic acid6 test tubes 0.05% ascorbic acidDroppers JuicerFunnel An orangeFilter paper 4 different brands of orange juiceBeakerMethodTASK 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 acidTASK 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
  2. 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 samplesResultsTASK 1 Number of drops required Trial #1 Trial #2 Trial #3 Average0.1% Ascorbic acid0.05% Ascorbic acidTASK 2 Number of drops required Trial #1 Trial #2 Trial #3 AverageFresh orange juiceCalculate % vol of ascorbic acid in orange juiceFormula No. of drops of ascorbic acid = x No. of drops of orange juice = %vol of AAEg 20 = x 50 = 0.1 2/5 = x/0.1 x = 2/5 * 1/10 x = 3/50 x = 0.06Calculations
  3. 3. TASK 3 Number of drops required Trial #1 Trial #2 Trial #3 AverageCalculate % vol of all 4 samplesDiscussion questionsQ1. On the supplied graph paper draw a bar graph to display a side-by-sidecomparison of all 5 samples of orange juice tested. Record the concentration onthe y axis.For the 4 commercial brands of orange juice, display a second bar indicating theclaimed concentration of ascorbic acid,Q2. How did each of the 4 commercial brands compare with regard to claimedand actual vitamin C content?
  4. 4. Q3. For any of the commercial brands that state the % of the drink that is actualorange juice, using vitamin C concentration as a basis for comparison, calculateand comment on the validity of these claims.Q4, What may account for any of the differences observed in your answer toquestion 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 thisrequirement 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 ofthe tested products for this purpose? Explain your answer.