✔ 最佳答案
concentration of what?
2010-10-25 23:35:41 補充：
someone above outlined the procedures, but not detailed enough.
1. weigh the equal mass of sample, mix with some water and blend.
2. filter the slurries, wash the residue with some water; the liquid obtained is mixed with the filtrate.
3. using volumetric flask, make up the solution to equal volume with water.
4. titrate with: DCPIP solution; or mix with equal volume of excess iodine solution, followed by back-titration with standard sodium thiosulphate solution, with starch solution as indicator.
5. from the result, calculate amount of vitamin C in each sample, in terms of mg vitamin C / unit mass of sample.
to improve accuracy / efficiency / reduce difficulty, you can:
I. if you use DCPIP solution, you can also prepare a set of standard solutions of ascorbic acid (vitamin C), and draw a calibration curve. on te curve, it shows volume of DCPIP used for every concentration of vitamic C. this save some time in calculations.
II. if you want to show that result is solely due to vitamin C (not other reducing agents like reducing sugars), you can heat the final filtrate in step (2) with hot water bath, such that all vitamin C is destroyed by heat.
(i guess a drop of copper(II) sulphate solution can be added, speeding up decomposition of vitamin C during heating).
III. you may want to dilute the plant extract in case they're too concentrated and cause some problems in titrations.
