bio lab.report,help please!!!

Aim:
To find out the concentration of vitamin C

Introduction:
Vitamin c is a strong reducing agent. It's reducing power is important for its functions. Vitamin C van reduce blue dye DCPIP and turn its colour from blue to colourless. This process is known as decolourization. Thus, we can estimate the amount of vitamin c by comparing the volume of vitamin solution needed to decolourize a certain volume of DCPIP solution.

Procedure:
1. Use a syring without a needle to put 1cm3 of DCPIP solution (blue) in a test tube
2. Use a dropper to add 0.1% vitamin c solution, drop by drop, to the DCPIP solution. Stop once you note any colour changes. Record the volume of vitamin c solution added.
3. Repeat the above steps using tea.
4. Record the volume of juice needed to decolourize the same volume of DCPIP solution in each sample.

Precautions:
Since DCPIP is unstable in air at room temperature, do not shake the test tube too much when mixing them.
Rinse the syringe thoroughly before obtaining each type of tea.

Result:
Concentration=volume of 0.1% vitamin solution added * 0.1% / volume of tea sample added

Then, you can calculate the amount of vitamin c.

Discussion:

1. Do you need to measure the volume of DCPIP solution and vitamin solution accurately?
Yes, accurate measurement is necessary in this quantitative experiment.

2. It is not recommended to shake the test tubes too much. Explain.
DCPIP are unstable. The reducing power will be affected by the oxygen in the air bubbles produced by shaking.

2013-01-09 10:17:49 補充：
If you see "juice", change it to "tea". It is because my school use juice instead of tea.