To investigate how temperature affects the concentration of vitamin C in orange juice (specifically 'Just Juice').

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Biology Coursework -Vitamin C

Apparatus: Burette, Test tubes, Retort stand, Bunsen burner, Measuring Cylinder, Beaker.

Materials: Orange juice, Water, Indicator (Dichlorophenolindophenol) abbreviated (DCPIP)

                                       Burette filled with 50 cm3 DCPIP    

                                           Orange juice         

Aim:

To investigate how temperature affects the concentration of vitamin C in orange juice (specifically ‘Just Juice’).

Hypothesis:

I predict that if I increase the temperature of the orange juice, the concentration of the orange juice will decrease. This is because vitamin C is a fairly unstable molecule, and the greater the heat the more vitamin C molecules will be broken down. It takes activation energy to break down bonds and as we are heating the orange juice the energy used to break the vitamin C inter-molecular bonds is heat energy. This is because the bonds holding the vitamin C molecule together are being broken, and the more heat energy available the more vitamin C bonds can be broken. So by increasing the temperature I will expect to need less DCPIP to change the colour of the orange juice to the standard I have chosen (when the solution has turned a purply-brown colour). I predict that when I plot a graph of temperature against volume of DCPIP used, I will get a straight-line, indicating direct correlation between the two.

Method: In order that we obtained the most accurate results possible, I conducted a preliminary experiment. This helped me gauge what quantities of substances would give me the best results, and the most practical method available. Thus my actual set of results and the method for the final experiment differ somewhat from my preliminary results and method.

   Preliminary method: After setting up the titration apparatus and pouring in 25 cm3 of orange juice, I measured the temperature of the orange juice. Recording this I added DCPIP until the solution turned purply-brown. I kept this colour as the standard colour to indicate when the reaction had finished, and managed to control the amount of DCPIP very precisely due to the burette which dripped slowly into the beaker. Knowing the amount of DCPIP needed to react with the orange juice at room temperature gave me an idea of the amount of vitamin C in the solution compared to the amount in heated solutions of orange juice. The more vitamin C in the solution, the more DCPIP needed to react with it.

        I heated solutions of orange juice to 41, 51 and 61 degrees centigrade. Then with two repeats for a higher accuracy, I measured the amount of DCPIP needed to make each solution react and turn purply brown.

  The real deal (Actual Experiment): As the preliminary results had taken too much time to obtain due to me having to heat each solution one at a time, I decided to make use of the water bath. This meant I could do two repeats at each temperature in the time it would take to just find the amount of DCPIP needed at one temperature. This speeded things up and I kept my method the same as my preliminary. The only difference I made was in using 10 cm3 of orange juice; thereby reducing the amount of DCPIP needed and quickening the time to find the amount of DCPIP needed.  

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Introduction:

       The positive effects on a person’s health that are brought about by vitamin C have been obvious to the ancient civilisations such as the Egyptians, whose herbal remedies and knowledge about healing far exceeded what we would expect from a civilisation more than 2000 years old. In more recent times in the West, it was James Lind who first realized that vitamin C is a necessary part of a man’s diet, after witnessing the healing effect of c=vitamin C on his men who were suffering from ...

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