Stephanie Chan 12HT

Biology HL – Mr. Etheridge

Vitamin C Investigation


Ascorbic acid, commonly known as Vitamin C, is a water soluble, essential vitamin for the body (meaning that it has to be acquired from our diet). It has the molecular formula of C6H8O6 and the structural formula can be seen on the right. Vitamin C is vital for the formation of collagen, a main component of connective tissues and the basis for the general shape and structure of the body. Vitamin C not only serves as an integral part of maintaining the function of blood vessels, bones, teeth and many other various connective tissues, it is also an antioxidant. This function allows the Vitamin C to protect the body from other water soluble molecules that could create free radicals (atoms which may cause damage and mutation to cells) when oxidised. Furthermore, it has also been shown in research that Vitamin C stimulates the immune system, and coupled the antioxidant function, it may help prevent and treat infections and diseases (generally used to combat the common cold).

Because Vitamin C is a strong reducing agent – hence its function as a good antioxidant – it can also be easily changed by oxidising agents. This is particularly evident when Vitamin C is exposed to atmospheric oxygen, the concentration will be reduced due to the ascorbic acid oxidising with the surrounding air, and in addition, ascorbic acid is also sensitive to light. This experiment will study temperature, an abiotic factor, on how it affects Vitamin C by calculating its concentration in lemon juice by titrating lemon juice against dichlorophenolindolephonol (DCPIP) and see how much DCPIP is needed to decolourise a controlled amount of lemon juice (2cm3).


Design a quantifiable investigation to look at the effect of at least one abiotic factor – in this case temperature – on Vitamin C.



I think that as the temperature increases, the Vitamin C concentration within the lemon juice will decrease. This is so because when Vitamin C is exposed to the air, it oxidises, modifying the vitamin into dehydroascorbic acid, hence reducing the concentration of ascorbic acid in a solution. Therefore I think that when the temperature of the lemon juice increases, the Vitamin C’s reaction with atmospheric oxygen will increase, lessening the concentration of Vitamin C as it oxidises into dehydroascorbic acid – therefore, the higher the temperature, the smaller the concentration of Vitamin C in the lemon.


        Independent – temperature (10°C, 25°C, 40°C, 55°C)

        Dependent – amount of DCPIP needed to decolourise 2cm3 lemon juice (cm3)

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        Controlled – amount of lemon juice used (2cm3)


Equipment – one 100cm3 and three 500cm3 beakers, labels, a fresh lemon, a knife, 10cm3 pipette, burette, retort stand, safety mat, conical flasks, test tubes, test tube rack, water baths at 50°C and 80°C, thermometer, DCPIP (1% aqueous solution), deionised water, ice, funnel, pipette bulb

  1. Gather and set up all equipment as shown

  1. Label one 500cm3 beaker, “waste”
  2. Label the other 500cm3 beaker, “lemon juice”
  3. Pour some DCPIP from the big jug into 100cm3 ...

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