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How does cooking affect the amount of vitamin C in lemon juice?

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Introduction

´╗┐AHMAD LUTFI BIN MOHAMAD M08G Title: Measuring the concentration of vitamin C. Research Question: How does cooking affect the amount of vitamin C in lemon juice? Hypothesis: The longer the lemon juice is cooked up to the boiling temperature, the lower the concentration of vitamin C. Variables: 1. Independent: Type of lemon juice samples [fresh lemon juice (0 minute boiled) , 10 minutes boiled lemon juice, 1 hour boiled lemon juice]. 2. Dependent: The concentration of vitamin C. 3. Constant: 1. The volume of DCPIP solution used. In each trial, 1 cm3 of DCPIP solution is used. 1 cm3 is chosen because it is neither too much nor too little since too much DCPIP solution used will need high amount of lemon juice to decolourise. In fact, the volume needs to be fixed as different volume of DCPIP solution requires different volume of lemon juice to decolourise. 2. The volume of lemon juice used for dilution. 4 cm3 of each type of lemon juice is used to make up 100 cm3 solution. The volume must be constant as if different amount of lemon juice is used in the dilution, then there is no point of conducting the experiment since the data for each condition of lemon juice does not correspond and tally to each other. ...read more.

Middle

Hence: CjCs = 100%4% Cj = 25 × Cs Where Cs = 0.05 mg / volume of diluted lemon juice sample titrated. From the formula derived, the concentration of vitamin C in lemon juice sample (Cj) can now be calculated. Below is an example of calculation made to find the concentration of vitamin C in fresh lemon juice. Cj (fresh lemon juice) = 25 × 0.05 mg32.60 cm³ = 3.834 × 10-2 mg cm-3 Uncertainties: Percentage uncertainty of volume of diluted lemon juice titrated = 0.10 cm³32.60 cm³ ×100% = 0.307% Percentage uncertainty of DCPIP = 0.1 cm³1.0 cm³ ×100% = 10.0 % Total percentage uncertainty of the concentration of vitamin C in fresh lemon juice, = 0.307% + 10.0 % = 10.307% Therefore, the concentration of vitamin C = 3.834 × 10-2 mg cm-3 ± 10.31% in fresh lemon juice Hence, the concentration of vitamin C in all samples of lemon juices can be presented in the following table: Lemon Juice Sample Concentration of Vitamin C (×10-2 mg cm-3) Fresh lemon juice 3.834 ± 10.31% 10 minutes boiled lemon juice 3.030 ± 10.24% 1 hour boiled lemon juice 4.160 ± 10.33% Table 4 the concentration of vitamin C in different lemon juice samples. ...read more.

Conclusion

DCPIP is very sensitive to heat, thus the warm sample titrated into DCPIP will cause the DCPIP to decolourise faster. The sample should be left about 10 minutes for it to cool down before being used in the titration. This will ensure that the DCPIP is in optimal condition thus no other factor will cause it to decolourise faster other than because of the presence of ascorbic acid. The dilution of lemon juice samples is done in a 100 cm3 measuring cylinder. It is quite difficult to shake the solution inside a measuring cylinder (a step which is supposed to be done in dilution process) and the huge uncertainty of measuring cylinder could greatly affect the reliability of the data obtained. The dilution process should be done in a volumetric flask since it has a smaller uncertainty and the apparatus itself is invented and meant for dilution. The three lemon juice samples are prepared from different lemon fruits. Problems and inaccuracies might arise as different lemon fruits contain different concentration of vitamin C thus causes the data obtained to be defective. The lemon fruits should be prepared together. Then, all the lemon juice prepared should be mixed together before being separated into 3 samples. This will ensure that all the three samples have relatively the same. ...read more.

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