Determination of the concentration of vitamin C by using DCPIP test

1. Practical investigation Determination of the concentration of vitamin C by using DCPIP test

2. Squeezing pipette/dropper pipette & pipette filler Test-tube & test-tube rack Apparatus required:

3. DCPIP solution Blue colour Materials required:

4. DCPIP = Dichlorophenol-indophenol

5. Juices from different sources

6. Squeeze the fruits and get the juices… in this way? or in this way? or…

7. Juices must be freshly prepared

8. Which one of them gets more vitamin C ? Notice that while Kiwi fruit is rich in vitamin C, it is not a citrus fruit.

9. Citrus fruits are rich in vitamin C.

10. Pink Colourless Blue A few steps in titration Juice titrates against DCPIP solution DCPIP solution changes to pink colour DCPIP solution changes to colourless

11. How to transfer 1 ml of DCPIP solution to a test tube by using pipette? How to titrate vitamin C solution against 1 ml of DCPIP solution How to titrate juice against 1 ml of DCPIP solution

12. Precaution: Drop size must be constant. Press the squeezing pipette gently.

13. The pipettes must be carefully cleaned by distilled water and rinsed with the solution to be taken up.

14. During determination, the dropper must be held vertical and the fruit juice should not flow down the side of the test tube.

15. At least three experimental trials must be taken and the average number of drops calculated.

16. 20 drops of juice B is required 15 drops of juice A is required Question: To decolourize the DCPIP solution Which one gets more vitamin C in it ? Answer: juice A

17. How to work out the concentration of vitamin C in different juices? Concentration of standard solution Concentration of vitamin C in fruit juice Volume of standard solution Volume of fresh juice X

18. Notice that mathematically, it is an inverse relation, 反比!