Bio Sba#2

SBA#2 Topic: Quantitative Analysis of Ascorbic Acid Date: October 16, 2018 Skill: Observation Recording Reporting (ORR)

Aim: To determine the concentration of ascorbic acid in orange juice

Apparatus and Materials:      

Standard solutions of ascorbic acid (0.5, 1.0, 2.0, 4.0, 5.0 and 6.0 mg/𝑐𝑚3 Dichlorophenolinolphenol (DCPIP) Test tubes Test tube racks Syringes Orange juice

Method: 1. 2. 3. 4. 5. 6. 7.

A dropper was used to add 1 𝑐𝑚3 of DCPIP to a test tube and the test tube was placed in a rack. A syringe was filled with 5 mg/𝑐𝑚3 of ascorbic acid. The ascorbic acid was added drop by drop to the DCPIP solution. The number of drops of ascorbic acid needed to decolourise the DCPIP solution were counted and recorded in a table The procedure was repeated using a fresh sample of DCPIP solution. The procedure was repeated using the other 5 concentrations of ascorbic acid and orange juice. A graph was plotted to show the number of drops of ascorbic acid solution against the concentration of ascorbic acid.

Observation: As ascorbic acid was being added to the DCPIP, the DCPIP slowly changed from blue to pink and then finally to a colourless solution. It was observed that orange juice was the least concentrated.

TABLE SHOWING THE NUMBER OF DROPS OF ASCORBIC ACID AND ORANGE JUICE NEEDED TO DECOLOURISE THE DCPIP SOLUTION Conc. of ascorbic acid (mg/cm3) 0.5 1.0 2.0 4.0 5.0 6.0 Orange Juice

Number of drops needed to decolorize DCPIP 1 2 Average 80 54 67 73 64 68.5 58 39 48.5 35 61 48 46 41 43.5 23 16 19.5 165 130 147.5

Discussion: Ascorbic acid is a six carbon compound which is related to glucose, its chemical formula is C6H8O6. It is found naturally in citrus fruits such as oranges and lemons and it is also found in some vegetables. Ascorbic acid is an essential nutrient in human diets. It is a form of vitamin C and functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant. Ascorbic Acid is a natural water-soluble vitamin. Ascorbic acid is a potent reducing and antioxidant agent that functions in fighting bacterial infections, in detoxifying reactions, and in the formation of collagen in fibrous tissue, teeth, bones, connective tissue, skin, and capillaries. It cannot be produced or stored by humans and must be obtained in the diet. Since ascorbic acid is a reducing agent it has the ability to reduce other molecules and is oxidized in the process. This means that it can donate two electrons to another component. This can come in handy in a lot of different situations and plays an important role in the human body. However its oxidation will result in a new stable molecule called dehydroascorbic acid. Ascorbic acid is easily oxidized. In the experiment which was carried out the concentration ascorbic acid and orange juice were tested using the indicator DCPIP. The reaction which took place was a redox reaction where ascorbic acid was the reducing agent and DCPIP was the oxidant. As the ascorbic acid was added slowly to the indicator, it slowly changed it to the reduced colourless form of DCPIP. The more concentrated the ascorbic acid used the less number drops would be used to reduce the DCPIP as seen from the results. It was seen where the least concentrated was the orange juice while the most concentrated was the ascorbic acid of 6.0 concentration. However, it was seen where the 0.5 concentration of ascorbic acid took less drops to cause the indicator to become colourless than the 1.0 concentration. This was due to the 1.0 ascorbic acid being oxidized by the air therefore causing it to be seen as less concentrated.

Limitation:  

Oxygen concentration in the air was not constant Oxygen was in the air therefore the vitamin C in the ascorbic acid and orange juice was already slightly oxidized when being added to the DCPIP

Precaution:  

It was ensured that test tube was not shaken to prevent oxidization of the vitamin C. The ascorbic acid solutions were placed in a cupboard away to reduce oxidation when it was not being used.

Source of error: 

Drops of ascorbic acid solutions and orange juice solutions which were counted fell on the side of the test tube instead of directly in the solution.

Conclusion