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 drop5. Repeat until the solution goes colourless6. Take a note of how much you have added7. YOU SHOULD DO THIS A FEW MORE TIMES

AND AVERAGE THE RESULTS8. Record the exact amount you added9. 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 apparatus3. Describe the method4. 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 data9. Comment on any systematic or random errors10. 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 tested Volume of juice required to decolourise 1 cm3 of 0.1% DCPIP solution/cm3

Average of juice required /cm3

Vitamin C content of juice/mg cm–3

Grapefruit juice

1.50 1.70 1.65

Pineapple juice

12.00 11.20 11.50

Orange juice

2.00 2.25 2.10

Orange drink

1.40 1.50 1.45

Fresh lemon juice

1.90 1.70 1.60

Bottled lemon juice

24.0 23.5 24.5

Juice tested Volume of juice required to decolourise 1 cm3 of 0.1% DCPIP solution/cm3

Average of juice required /cm3

Vitamin C content of juice/mg cm–3

Grapefruit juice

1.50 1.70 1.65 1.61 3.8

Pineapple juice

12.00 11.20 11.50 11.56 0.5

Orange juice

2.00 2.25 2.10 2.12 2.8

Orange drink

1.40 1.50 1.45 1.45 4.1

Fresh lemon juice

1.90 1.70 1.60 1.73 3.5

Bottled lemon juice

24.0 23.5 24.5 24.0 0.25