Vitamin-C

Investigation (Junior Science)

Does boiling vegetables destroy the vitamin-C?

  

Aim - to determine the amount of vitamin-C remaining in a solution after boiling for a measured length of time.

Apparatus
- Mortar and pestle
- 15 g of KI and 3g of I2
- Starch
- Distilled water bottle
- Supply of fresh vitamin-C tablets (commercially available, 500 mg per tablet)
- 250mL volumetric flask
- 2 X plastic disposable pipettes
- 50 mL measuring cylinder
- Starch solution, used a as an indicator ( 5 mL)
- plastic funnel
- 100 mL beaker
- hot-plate
- 1 gram of starch

 

Preparation of the iodine solution.
Dissolve 15 g of potassium iodide (KI) in 125 mL of distilled water. Add 3 g of iodine (I2) and stir the mixture to dissolve all solutes. Dilute this solution by adding distilled water to make the volume up to 1 litre. Store in a dark bottle.

Preparation of starch solution.
Dissolve 1 gram of starch in 10 mL of distilled water, shake well. Pour the 10 mL starch solution into 100 mL of boiling, distilled water. Stir thoroughly and continue to boil for 1 minute. Leave to cool down. If insoluble products form then simply decant the supernatant and use as the indicator solution.

Step 1 Using the mortar and pestle crush one vitamin-C table into a fine powder.
Step 2 - Place the crushed tablet into a 250 mL volumetric flask.

 

 
Step 3 - Wash all the contents out of the mortar and into the volumetric flask using the distilled water bottle.

 
Step 4 - Fill the volumetric flask to the mark with distilled water. The last few drops of distilled water may need to be delivered with a pipette so as not to overshoot the mark. Shake to dissolve all particles.
Step 5 - Using a measuring cylinder place 10 mL of the vitamin-C solution from the volumetric flask into the measuring cylinder. The last few drops may need to be delivered using a  pipette so as to get as close as possible to 10 mL.
Step 6 - Place two drops of starch indicator in the measuring cylinder with the 10mL of vitamin-C solution.
Step 7 - Add, drop by drop, the iodine solution, while constantly stirring the solution in the measuring cylinder.

Stop adding iodine solution when the solution changes permanently to blue. Measure the amount of iodine solution delivered. Record your result.

 

The amount of iodine solution added is indicative of the relative amount of vitamin-C present.

Conduct an investigation to see what impact heating has on vitamin-C content.
Worksheet