Measuring the content of vitamin C in fruit juice

Question 1

What is the independant variable

Answer 1

Fruit juice

Question 2

What is the dependant variable

Answer 2

Volume of juice required to decolourise 1cm^3 of DCPIP

Question 3

What other variables need to be controlled (4)

Answer 3

• Temperature
• Concentration of DCPIP solution (1%)
• Shake each tube same number of times
• Same end point colour (no blue at all)

Question 4

What equipment is required (8)

Answer 4

• 1% DCPIP solution
• 1% vitamin C solution
• range of fruit juices
• test tubes/conical flasks
• beakers
• pipette accurate to 1cm3
• burette
• safety goggles

Question 5

Give outline of the method

Answer 5

pipette 1cm3 blue DCPIP into test tube. Using burette (or accurate pipette) add 1% vitamin C solution drop by drop. Shake tube gently after each drop. Continue until the blue colour just disappears. Record volume of solution needed to decolourise the DCPIP. Repeat further 2 times and calculate mean result. Repeat procedure with different fruit juices.

Question 6

Possible evaluation issues (5)

Answer 6

• 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