Vitamin C Determination By Iodine Titration Biology Essay

Vitamin C is also known as ascorbic acid, it is an antioxidant that is essential for human nutrition. Antioxidants help to reduce the damage to the body caused by toxic chemicals and pollutants. Vitamin C is a water-soluble vitamin meaning that it dissolves in water, it is essential for growth and repair of all body tissues. Collagen is an important protein that is used to make skin, scar tissue, tendons, ligaments and blood vessels. Vitamin C is essential to form this and is also required to cure wounds, repair and maintain cartilage, bones and teeth. The body does not store vitamin C and cannot make it by itself, therefore it is important for lots of vitamin C-containing foods to be included in the diet. Excellent sources of vitamin C are: green peppers, citrus fruits, strawberries, broccoli, papaya, watermelon and cauliflower. Vitamin C deficiency can lead to many problems in the body including: dry and splitting hair, bleeding gums, easy bruising, anemia and nosebleeds with one of the most serious being scurvy. Eating a balanced diet is the best way to get the daily requirements of vitamin C and other essential vitamins. The Food and Nutrition Board at the Institute of Medicine recommends the following amounts of vitamin C:

Infants and Children

0 – 6 months: 40 milligrams/day (mg/day)

7 – 12 months: 50 mg/day

1 – 3 years: 15 mg/day

4 – 8 years: 25 mg/day

9 – 13 years: 45 mg/day

Adolescents

Girls 14 – 18 years: 65 mg/day

Boys 14 – 18 years: 75 mg/day

Adults

Men age 19 and older: 90 mg/day

Women age 19 year and older: 75 mg/day

One way to establish the amount of vitamin C in food is to use a redox titration. The redox reaction is better than an acid-base titration since there are additional acids in a juice, but few of them interfere with the oxidation of ascorbic acid by iodine. Iodine is relatively insoluble, but this can be improved by complexing the iodine with iodide to form triiodide:

I2 + I- <–> I3-

Triiodide oxidizes vitamin C to form dehydroascorbic acid:

C6H8O6 + I3- + H2O –> C6H6O6 + 3I- + 2H+

As long as vitamin C is present in the solution, the triiodide is converted to the iodide ion very quickly. However, when the all the vitamin C is oxidized, iodine and triiodide will be present, which react with starch to form a blue-black complex. The blue-black colour is the endpoint of the titration.

Vitamin C – Ascorbic Acid

Method

The 1% starch solution, iodine solution and vitamin C solution were made up by the technicians. The solutions were standardised before the unknown samples were titrated using the following method:

25.00 ml of vitamin C standard solution was added to a 125ml Erlenmeyer flask

10 drops of 1% starch solution were added to the flask

The burette was rinsed with a small volume of the iodine solution and then filled, the initial volume was recorded.

The solution was titrated until the end point was reached

The final volume of the iodine solution was recorded

The titration was completed twice more.

Samples of red pepper juice, apple juice and vinegar were then titrated in the same way. This is an example of a titration:

Results

Sample

Your Hypothesis: high medium or low Vitamin C content?

Titration 1

Titration 2

Titration 3

Calculated Vitamin C content (g/l)

Your result versus the Hypothesis

Red Pepper Juice

High Vitamin C content

16.0

17.0

18.0

28.5

Correct

Apple Juice

Medium Vitamin C content

4.0

4.0

4.0

6.8

Correct

Vinegar

Low Vitamin C content

0.4

0.2

0.4

0.67

Correct

Analysis

The ml of titrant used for each flask is calculated using:

Average volume = total volume

number of trials

The amount of vitamin C in the samples are calculated using:

V itamin C titrant = Titrant used in Sample

Standard of Vitamin C unknown

Red Pepper Juice

       Titrant                       =        Used Sample         

Standard of Vitamin C           Unknown Vitamin C

    14.9ml          =     17 

  0.025g/ml               P

596 = 17.0

             P

P= 17.0                      P= 0.0285g/ml

      596

Litres = 0.0285 x 1000

          = 28.5g/litre

Apple Juice

       Titrant                       =        Used Sample         

Standard of Vitamin C           Unknown Vitamin C

    14.9ml          =     4.0  

  0.025g/ml               A

596 = 4.0

            A

A= 4.0                      A= 0.0067 g/ml

      596

Litres = 0.0067 x 1000

          = 6.8g/litre

Vinegar

       Titrant                       =        Used Sample         

Standard of Vitamin C           Unknown Vitamin C

    14.9ml          =     0.4  

  0.025g/ml              G

596 = 0.4

           G

G= 0.4                        G= 0.00067g/ml

      596

Litres = 0.00067 x 1000

          = 0.67g/litre

Discussion

One of the main problems when completing this experiment is that the concentration of solution was unknown as it was prepared by the technician, the concentration was too high so had to be diluted. The hypothesis was correct in that the red pepper juice had the highest vitamin C content, vinegar the lowest and apple juice medium. Many safety procedures were carried out during the experiment; safety glasses, gloves and goggles were worn, all bags and jackets were in the lockers and chairs were tucked under the desk. There was a good experience with the number of people in the group as it gave everyone a chance to be involved with the experiment. A reading was taken at the first point when the colour started to change and it could be seen easily when it was complete as the change happened gradually. Two examples of other food that are rich in vitamin C that were not tested are tomatoes and raspberries. Iron increases the absorption of vitamin C in the human body, iron is important as it is used by the body in the production of red blood cells, it is specifically used in the production of hemoglobin which is the main protein in red blood cells. Polyphenol oxidase, also known as tyrosinase, is an enzyme contained in fruits and vegetables such as apples, pears, potatoes, and other starchy foods. When oxygen comes in to contact with the enzyme it causes the fruit to turn brown. Vitamin C has many functions in the body, it is essential for growth and repair of all body tissues. Collagen is an important protein that is used to make skin, scar tissue, tendons, ligaments and blood vessels. Vitamin C is essential to form this and is also required to cure wounds, repair and maintain cartilage, bones and teeth. Anti-oxidant vitamins are Vitamins that help the body in cleansing itself from waste and radical free agents, Free radicals are atoms or groups of atoms with an (unpaired) number of electrons and can be formed when oxygen interacts with certain molecules. As well as vitamin C, vitamins A and E are also antioxidants. Vitamin A helps form and maintain healthy teeth, skeletal and soft tissue, mucous membranes, and skin. It is also known as retinol because it produces the pigments in the retina of the eye. Vitamin E is important in the formation of red blood cells and can help the body to use vitamin K. Selenium is an essential trace mineral that works strongly with vitamin E to provide the body with powerful antioxidant protection from the free radicals that may add to the development of cancer, heart disease, and arthritis. Selenium protects the body from free radical damage in two ways: It is included into proteins to make selenoproteins, which are important antioxidant enzymes, and it helps the body manufacture its own natural antioxidant, glutathione.

Conclusion

In conclusion, the experiment worked well as the amount of vitamin C in the samples was established and the results were accurate and as expected.