Vitamin C

Question 1

What’s the independent variable?

Answer 1

the fruit juice used

Question 2

What’s the dependent variable?

Answer 2

the volume of fruit juice needed to decolourise 1cm3 of DCPIP

Question 3

What are other variables to be controlled? (4)

Answer 3

• temperature
• concentration of DCPIP colution 1%
• shake each tube the same number of times
• same end point

Question 4

Equiptment needed. (name at least 3)

Answer 4

• range of fruit juices
• 1% DCPIP solution
• 1% vitamin C solution
• test tubes
• beakers
• pipettes
• burette
• safety goggles

Question 5

Describe the method.

Answer 5

1. pipette 1cm3 of blue DCPIP into test tubes
2. using a burette add 1% vitamin C solution drop by drop (shaking test tube after each drop) until the blue colour disappears
3. Record the volume of vitamin C solution needed to decolourise 1cm3 of DCPIP
4. repeat 2 more times to calculate a mean
5. repeat the procedure using 5 different fruit juices

Question 6

What are possible evaluation issues?

Answer 6

• difficulty in controlling temp
• amount of shaking
• difficult to judge end point
• some loss of solution when transferring from one container to another
• accuracy of measuring equipment