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Vitamin C lab (results&discussion)

Investigating the Ascorbic Acid Concentration of Various Fruits

Vanessa Braganza

CHEM 1811 – Section 04

September 14, 2012

Results and Discussion Section

In this study, ascorbic acid (1) contained in the juice of lemons, limes, and oranges was titrated with iodine (eqn 1) and the ascorbic acid concentration in each fruit was calculated.

Standardization of I 2 . Reduced ascorbic acid and iodine were combined in the presence of starch to produce oxidized ascorbic acid and hydroiodic acid.

The molarity of iodine was determined to be .019 M.

Titration of ascorbic acid . The volumes of titrant and analyte reacted, shown in Table 2, indicate that lime juice required the lowest volume of iodine to reach the endpoint of the titration, while orange juice required the greatest volume.

Table 1. Volume of iodine and fruit juice titrated.

Fruit

Volume of iodine (mL)

Total volume of fruit juice (mL)

Lime

Lemon

Orange

2.083 (1.925)*

2.552

3.638

45.10 (50.00)*

39.43

60.00

*Individual data are listed in parentheses.

Determination of ascorbic acid in lemons, limes, and oranges. The results of the titration, shown in Table 2, indicate that oranges contain the highest mass of ascorbic acid and limes contain the lowest mass. By contrast, oranges have the lowest mass to volume ratio and limes have the highest ratio. However, some groups used a tape measure to calculate the volume of the fruit, while others determined the volume through water displacement. This disparity in the methods by which each fruit was measured caused experimental error in the calculated average volumes of each fruit.

Table 2. Mass of ascorbic acid and volume of each fruit.

Fruit

Mass ascorbic acid (mg)

Volume of fruit (mL)

Mass to volume ratio

Lime

Lemon

Orange

7.137 (6.595)*

8.741

12.46

95.00 (105.0)*

146.7

254.7

.0751 (.0628)*

.0596

.0489

*Individual data are listed in parentheses.

Determination of fruit to pack. Based on ascorbic acid concentration and volume occupied, shown in Table 3, limes were determined to be the most efficient fruit to pack. With a molarity of 8.984 x 10 -4 M, limes had the lowest ascorbic acid concentration per fruit compared to lemons and oranges. Limes also required 10510 fruits for the journey, higher than lemons and oranges. However, the minimum required number of limes occupies only .998 m 3 , the lowest volume compared to lemons and oranges. This indicates that, while limes contain the lowest ascorbic acid concentration, they are the most effective in terms of spatial conservation. Consequently, they are the most effective fruit to pack on the trip. The volume occupied by the fruits was calculated with the assumption that there is no empty space between any stored fruits. This unduly reduced the predicted volume occupied by the fruits, causing error. The fact that the fruits were not all of uniform ripeness affected the ascorbic acid concentrations, causing error.

Table 3. Total volume, molarity, and number of fruits required.

Fruit

Ascorbic acid molarity

Number required

Volume occupied (m3)

Lime

Lemon

Orange

8.984 x 10-4

.0013

.0012

10510

8581

6019

.998

1.259

1.533

DMU Timestamp: September 14, 2012 19:31





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