Core Practical

 Vitamin C is an antioxidant  Which type of fruit juice provides the most vitamin C?  Is drinking fruit juice as good as eating fruit (for antioxidants)?  Fruit juice in cartons is long life (heat treated)

 Quantity of Vitamin C in food and drink determined by colour test  Vitamin C decolourises blue dye DCPIP  Vitamin C reduces the DCPIP  DCPIP changes colour in presence of vitamin C from blue to colourless (or slightly pink)

1. Syringe 1cm3 of DCPIP solution into a test tube 2. Draw some vitamin C solution into the pipette – MAKE SURE YOU KNOW HOW MUCH YOU HAVE IN THERE 3. Add the 1% vitamin C sample to the test tube drop by drop 4. Shake gently after each drop 5. Repeat until the solution goes colourless 6. Take a note of how much you have added 7. YOU SHOULD DO THIS A FEW MORE TIMES AND AVERAGE THE RESULTS 8. Record the exact amount you added 9. Repeat the procedure with the other samples

 The 1% solution contains 10mg of vitamin C per 1cm3  What is the mass of vitamin C required to decolourise 1cm3 of the DCPIP? (in mg per cm3)

1. What is the question you are testing? 2. List of apparatus 3. Describe the method 4. What are the independent (type of solution/vitamin C content) and dependent (volume of solution dropped in to decolourise) variables? 5. What other variables might affect the results (temperature, other chemicals present, age of juice)? 6. What is the control (1% vit C solution)? 7. Why do the replicates (for reliability)? 8. Discuss and support your conclusions with relevant biological knowledge and evidence from data 9. Comment on any systematic or random errors 10. What changes would you make and why - do more repeats? (reliability), use a colorimeter to measure colour change? (validity), use a different control e.g. water (validity)?

Juice testedVolume of juice required to decolourise 1 cm 3 of 0.1% DCPIP solution/cm 3 Average of juice required /cm3 Vitamin C content of juice/mg cm –3 Grapefruit juice Pineapple juice Orange juice Orange drink Fresh lemon juice Bottled lemon juice

Juice testedVolume of juice required to decolourise 1 cm 3 of 0.1% DCPIP solution/cm 3 Average of juice required /cm3 Vitamin C content of juice/mg cm –3 Grapefruit juice Pineapple juice Orange juice Orange drink Fresh lemon juice Bottled lemon juice