GAN ENG SENG SCHOOL

Republic Polytechnic Scientific Thinking Programme 2008

Vitamin C content in local vegetables and how cooking affects Vitamin C

content

Gan Eng Seng School Team 2

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• To determine the concentration of Vitamin C present in 4 common vegetables.

• To determine if the duration of boiling will affect the concentration of Vitamin C in 1 of the 4 local vegetables.

Aim

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Hypothesis

• Boiling will result in the decrease in the concentration of Vitamin C. The longer the duration, the lower the concentration of Vitamin C left in the vegetable.

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Methods

• 4 different vegetables were selected to determine the Vitamin C concentration using iodometric titration.

• Excess iodine will then react with the starch indicator to form the starch-iodine complex, which marks the end point of titration. This is when the first permanent trace of dark-blue coloration is observed due to the formation of the starch iodine complex.

Ascorbic acid + I2 2I- + dehydroascorbic acid

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Determining the concentration of the prepared iodine solution

1. Dilute 1 Redoxen Effervescence Vitamin C tablet (1000mg of Vitamin C) in 1000ml of iced water.

2. Adding another 100m of iced water further dilutes 100ml of the diluted solution.

3. 25ml of this standard solution and 3ml of starch indicator solution is pipette into a conical flask and titrated against the iodine solution.

4. Iodine solution was added slowly into the standard solution and stopped when the first permanent trace of blue-black coloration is observed.

5. Titration was repeated for a total of 3 times or more until concordant results

(within the range of 0.1cm3) were obtained.

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Determining concentration of Vitamin C in 4 different vegetables

1. Chop each type of vegetables into fine pieces using a knife on a chopping board.

2. Blend 100g of the chopped vegetables and 200ml of iced water for 2 minutes.

3. Iced water was added as the heat generated by the blender may destroy some of the vitamin.

4. The blended mixture is strained through a cheese cloth and collected in a beaker. The beaker was placed in ice to keep the mixture cold.

5. Titration was carried

1. The green peppers were chopped into fine pieces using a knife on a chopping board.

2. 100g of the chopped vegetables were then added to boiling water and was boiled for a fixed duration (1min, 5min, 10min, 15min, 20min, 25min, 30min, 35min and 40min).

3. After boiling for a fixed duration, the boiled green peppers were removed and placed into the blender.

4. Titration was then carried out

Determining the concentration of vitamin C in green pepper

after boiling

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Concentration of vitamin C present in 4 common vegetables.

Vegetable Concentration of Vitamin C (mg / 100g)

Broccoli 52.8

Cabbage 25.1

Carrot 11.6

Green Pepper 88.8

Green pepper has the highest concentration of vitamin C

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The effect of the duration of boiling on the concentration of Vitamin C in green pepper

Change in concentration of Vitamin C

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40

Time (min)

Co

nc

en

tra

tio

n (

mg

/10

0g

)

The concentration of vitamin C decreases as the duration of boiling increases

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Significance of the experiment

• The group found evidence that cooking the vegetables decreases the vitamin C content of the vegetable. To retain the Vitamin C content, we feel that it is necessary to keep the cooking time to a minimum.

• Suggestions for Improvement – The determination of Vitamin C content in the

vegetables can be done using Vitamin C indicator kits.

– Other similar experiments can be conducted. For example, we investigate how storage conditions affect the concentration of vitamin C in vegetables.

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What have we learnt

• Analyse raw data and how to present it in a scientific manner.

• Search for information and compile selected information together.

• Scientist mindset, never give up, if fail, try again.

• Work together as a team.

• Ask questions.

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Acknowledgements

1.      Miss Kong Ching Ying2.      Ms. Melanie Wong (Republic Polytechnic Supervisor)3.      Ms. Junainah Badron (Republic Polytechnic Supervisor)4.      Gan Eng Seng School Laboratory Technicians 

References 

1.http://en.wikipedia.org/wiki/Vitamin_C2.http://www.nlm.nih.gov/medlineplus/ency/article/002404.htm3.http://www.lenntech.com/fruit-vegetable-vitamin-content.htm4.http://en.wikipedia.org/wiki/Capsicum

GAN ENG SENG SCHOOL

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Iodometric Titration

• Titration: Titration is a commonly used technique in Chemistry to determine the concentration of a chemical (titrant) by adding a measured volume of another chemical (titrating solution) with a known concentration until the formation of a coloured complex. The concentration of the titrant can be then be calculated using stoichiometry based on the volume of titrating solution added.

• Iodine titration: The titrant in this experiment is ascorbic acid and the titrating solution is iodine solution. Starch indicator solution is also added into the titrant. The two solutions react according to the following equation:

Ascorbic acid + I2 2I- + dehydroascorbic acid

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