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Vitamin C Lab

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Introduction

Stephanie Chan 12HT Biology HL - Mr. Etheridge Vitamin C Investigation Introduction 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. ...read more.

Middle

Vitamin C And from one titration, 2.10cm3 DCPIP decolourises 2.00cm3 of Vitamin C, To calculate concentration of Vitamin C, the amount of DCPIP must equal to 2cm3 for the data to be quantifiable and equivalent to the standard, hence In order for the 2.10cm3 DCPIP to equal to 2.00cm3, it must be multiplied by (2/2.10) cm3 DCPIP = 0.95 And to keep the ratio of 2.00cm3 of 1% DCPIP decolourises 4.00mg of 0.1% Vitamin C the same, Lemon Juice = 0.95 � 2.00cm3 = 1.90 cm3 Hence, 1.90cm3 of lemon juice contains 4mg is required to decolourise 2cm3 of DCPIP, 4.00mg Vitamin C/1.90cm3 lemon juice = 2.10mg Vitamin C/1 cm3 Lemon Juice Because 1mg of Vitamin C is in 1cm3 of solution, or 0.1%, Therefore the concentration of 1.05mg/cm3 Vitamin C in 1cm3 lemon juice is = (2.10 � 0.1%) � 100 = 0.210% Uncertainties Pipette uncertainties: The pipette used in this experiment measures 2.00cm3 of lemon juice � 0.04cm3. The uncertainty due to the pipette is thus (0.04/2) � 100 = 2% Burette uncertainties: Lemon Juice at 10�C Uncertainty (cm3) / Measurements (cm3) � 100 Uncertainty Percentage (%) �0.1 20.7 0.48 22.3 0.45 Overall uncertainty (%) + 2 (uncertainty of the pipette) 2.93 Lemon Juice at 25�C Uncertainty (cm3) ...read more.

Conclusion

This mistake could lead to a great unreliability in our data (particularly the titrations done in the latter parts of the entire experiment) due to the addition of oxidised Vitamin C from being exposed to the air. Another aspect we could have improved upon was the amount of time each test tube of lemon juice spent inside the water bath, as the decomposition of the concentration of Vitamin C can vary depending on how long it has been heated for. Another problem with our method regarding the heating of the lemon juice was that the temperature of our lemon juice was not constant, particularly when we placed the lemon juice in the 80�C water bath and waited for the temperature to drop to 55�C. This method an unreliable way to see how 55�C would affect Vitamin C because the oxidation rate would have been different at 80�C than it would have been if the temperature had stayed at 55�C. In addition, a possible further experiment could be done to see the relationship between Vitamin C concentrations in a solution to the different amounts of time of heating it at a constant temperature (not at room temperature). Another way to make this experiment easier to calculate the results is to filter the lemon juice through filter paper so we could titrate the lemon juice in a burette like we normally have in previous determining Vitamin C concentration experiments. ...read more.

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