Measuring the content of Vitamin C in fruit juice

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  1. What is the independent variable in the experiment?
    Fruit juice/ type of food
  2. What is the dependent variable in the experiment?
    volume of juice required to decolourise 1cmof DCPIP
  3. Describe an experiment needed to measure the amount of vitamin C is present? ( 9 marks)
    • Firstly you need to create a calibration curve. This is done by firstly creating 6 different solution of known vitamin C concentration
    • Then you measure out at set volume of DCPIP into the test tube.
    • Then using a pipette, chose a vitamin c solution, extract it and drop by drop add it to the DCPIP, shaking it for a set period of time each time its added.
    • When the solution turns from blue to colourless, record the volume of Vitamin C that has been added.
    • Repeat the experiment twice more, with the same solution, and take an average of all 3 readings.
    • Repeat the above procedure with each solution.
    • Use the results to make a line graph, showing volume of vitamin C solution against its concentration.
    • Then with your unknown solution, using a pipette, add drop by drop the unknown solution to a test tube with DCPIP until it becomes colourless. 
    • Then using your calibration curve you can find the concentration of Vitamin C in your solution.
  4. What variables need to be controlled in the experiment? ( 4 marks)
    • Temperature
    • Concentration of DCPIP solution (1%)
    • Shake each tube same number of times
    • Same end point colour. i.e. until the blue colour of DCPIP just disappears
  5. What sources of errors could arise from the DCPIP experiment (5 marks)
    • Difficulty in controlling temperature
    • Amount of shaking (too much adds oxygen which will slightly restore the DCPIP to blue)
    • End point difficult to judge as needs to be just when blue colour disappears especially in highly coloured juices
    • Some loss of solution when transferring from one beaker to another
    • Accuracy of measuring equipment
Card Set
Measuring the content of Vitamin C in fruit juice
AS Biology Unit 1
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