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My name is Poon Cheng Moh. I have been teaching biology in SMK(P) Raja Zarina, Port Klang for 24 years. I sincerely hope that this blog on SPM Biology will be useful to both teachers and students.

Wednesday, July 20, 2011

Vitamin C content in fruit juices

Please read either from Hands on Pg 55 /the sample experiment plan given below :

Objective

To determine the vitamin C content in pineapple, lime and orange juice.

Problem statement

Which fruit juice contains the highest concentration /percentage of vitamin C?

Hypothesis

Lime juice contains higher concentration/percentage of vitamin C compared to pineapple juice and orange juice.

Variables

Manipulated : Types of fruit juice

Responding : Concentration/percentage of vitamin C in fruit juices

Constant : Volume of fruit juices/concentration of DCPIP solution/ Standard concentration of ascorbic acid solution

Apparatus and materials

Materials : freshly prepared pineapple, lime and orange juices, 0.1% ascorbic acid solution, DCPIP solution

Apparatus : 5ml syringe(with needle), 1ml syringe, specimen tubes, 5ml measuring cylinder

Technique

Measure and record the volume of fruit juice needed to decolourise 1 ml DCPIP using a syringe//

Calculate the % of vitamin C in fruit juice by using formula :
Vol of 0.1% ascorbic acid X 0.1
Volume of fruit juice

OR

Calculate the content of vitamin C in fruit juice by using formula :
Vol of 0.1% ascorbic acid (mgcm-3)
Volume of fruit juice

Procedure

1. 1 ml of DCPIP solution is placed in a specimen tube using a 1 ml syringe.
2. 5 ml syringe was filled with 5 ml of 0.1% ascorbic acid solution.
3. The needle of the 5 ml syringe was immersed into the DCPIP solution.
4. Ascorbic acid solution was added drop by drop until the DCPIP solution, and gently stirred with the needle of the syringe. (Do not shake the tube vigorously).
5. Ascorbic acid solution is added continuously until the DCPIP solution is decolourise.

6. The volume of ascorbic acid solution used measured using a syringe and recorded.
7. Steps 1-6 are repeated using fresh orange, pineapple and lime juice.
8. The volume of fruit juices required to decolourise the DCPIP solution in each fruit juice is measured using a syringe and recorded in a table.
9. The percentage and the concentration of vitamin C in each fruit juice are calculated using the above formula.

Precaution:

1. The juice must be freshly prepared.

2. Do not shake the DCPIP too vigorously.

Recording data/ result

Solution/

fruit juice

Volume of solution/fruit juice needed to decolourise 1 ml of DCPIP solution (ml)

Percentage of vitamin C (%)

Conc. of vitamin C (mg cm-3)


1

2

3

Average



0.1% ascorbic acid







Pineapple juice







Lime juice







Orangejuice







Conclusion

Lime juice contains higher concentration/percentage of vitamin C compared to pineapple juice and orange juice. Hypothesis is accepted.

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