Biochem. Lab 5 Determination of Vitamin C Concentration in Various Juice Sample PDF

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Biochemistry Laboratory Report

Experiment 5: Determination of Vitamin C

Concentration in Various Juice Sample

Names & ID Numbers: Christopher Mclean 1401013, Joel Taylor 1506692, Alecia Barrett 1701637

Lab Supervisor: Dr. S. Campbell

Session: Friday 2-5 pm 5/11/18

Aim To determine the quantity of vitamin C (ascorbic acid) found in various commercial juice samples by redox titration method with potassium iodate in the presence of potassium iodide. Introduction Ascorbic acid (vitamin C) is a structurally simple, water soluble organic acid found mostly in citrus fruits such as oranges lemons. Plants synthesize the compound for the growth, development, and protection of the plant. Deficiency in Vitamin C can lead to a variety of adverse health effects in humans, the most common of which is scurvy, which is characterized by abnormalities in the bones and teeth. In this experiment the amount of vitamin C in various juice samples will be determined by redox titrations. The redox reaction is better than an acid-base titration since there are additional acids in a juice, but few of them interfere with the oxidation of ascorbic acid by iodine.

Ascorbic Acid is a mild reducing agent The Ascorbic Acid itself is oxidized to a higher oxidation state. This class of reactions is known as a reduction/oxidation reaction or simply, a redox reaction. The equivalence point of the titration will be determined using a starch indicator. Molecular iodine combines with starch to make a dark blue complex. In the titration reaction, molecular iodine is added in the form of the iodine solution. In the presence of ascorbic acid, the iodine is reduced to colorless iodide ion which does not react with starch to make a colored complex. When all of the ascorbic acid has been titrated, any additional iodine added, present in the solution as molecular iodine, will combine with the starch to make the solution blue. The appearance of the blue solution will signal the equivalence point.

Results Table 1: Standardization of the Iodine Solution with the Vitamin C Standard Solution Trial

1

2

3

Final Volume (cm3)

16.60

31.20

45.70

Initial Volume (cm3)

1.90

16.60

31.20

Volume Used (cm3)

14.70

14.60

14.50

Average Volume (cm3)

14.60

Table 2: Titration of Mott’s Apple Juice at Room Temperature Trial

1

2

3

Final Volume (cm3)

14.20

31.20

32.50

Initial Volume (cm3)

5.00

16.60

23.50

Volume Used (cm3)

9.20

9.30

9.00

Average Volume (cm3)

9.17

Table 3: Titration of Bag Drink at Room Temperature Trial

1

2

3

Final Volume (cm3)

15.70

16.20

16.70

Initial Volume (cm3)

15.10

15.70

16.20

Volume Used (cm3)

0.60

0.50

0.50

Average Volume (cm3)

0.53

Table 4: Titration of Welch's White Grape Juice at Room Temperature Trial

1

2

3

Final Volume (cm3)

1.90

3.80

5.60

Initial Volume (cm3)

0.10

1.90

3.80

Volume Used (cm3)

1.80

1.90

1.80

Average Volume (cm3)

1.83

Table 5: Titration of Ocean Spray White Cranberry Juice at Room Temperature Trial

1

2

3

Final Volume (cm3)

7.20

8.50

9.70

Initial Volume (cm3)

5.90

7.20

8.50

Volume Used (cm3)

1.30

1.30

1.20

Average Volume (cm3)

1.27

Table 6: Titration of Boiled White Cranberry Juice Trial

1

2

3

Final Volume (cm3)

10.20

10.40

10.80

Initial Volume (cm3)

9.90

10.20

10.40

Volume Used (cm3)

0.30

0.20

0.40

Average Volume (cm3)

0.30

The equations for the reaction are as follows: - (1) KIO3 (aq) + 6 H+ (aq) + (l) + K+(aq)  5 I (aq) → 3 I2 (aq) + 3 H2O  Reaction one generates aqueous iodine, I2(aq)  . This is then used to oxidize vitamin C In reaction two. Both of these reactions require acidic conditions and so dilute hydrochloric acid, H2SO4(aq), will be added to the reaction mixture.  . This will be Reaction one also requires a source of dissolved iodide ions, I-(aq) provided by adding solid potassium iodide, KI (s), to the reaction mixture. - + (2) C6H8O6 (aq) + C6 H  I2 (aq) →   6 O  6 (aq) + 2 I (aq) + 2 H (aq)  (oxidation of vitamin C) Reaction 2 involves the oxidation of vitamin C and the reduction of the aqueous iodine molecule (I2 (aq)) with Ascorbic Acid to form dehydroascorbic acid.

Calculations For Vitamin C Standard Solution ● Average volume of titrant used for standard = volume used per trial / no. of trials (14.70 + 14.60 + 14.50) cm3 / 3 = 14.60 cm3 ● Expected volume of Iodine solution required to react with 0.250 g of ascorbic acid. From the equation the mole ratio is 1:1, therefore the no. of moles of C6H8O6 (ascorbic acid) = the no. of moles of Iodine  no. of moles ascorbic acid = mass of ascorbic acid / molar mass of ascorbic

acid = 0.250 g / 176.12g /mol  = 1.42*10-3 mol ⇒ 1.42*10-3  mol Iodine volume of Iodine solution = no. of moles of Iodine / concentration of Iodine solution. Concentration of Iodine solution = (no. of moles of Potassium Iodide + no. of moles of Potassium Iodate) / volume of solution no. of moles of Potassium Iodide = 10 g / 166.0028 g /mol = 0.0602 mol no. of moles of Potassium Iodate = 0.536 g / 214.001 g/mol  = 0.00250 mol concentration of Iodine solution = (0.0602 + 0.00250) mol / 1 L = 0.0625 M volume of Iodine solution = 1.42*10-3 mol / 0.0625 mol/L = 0 .0227 L For Mott’s Apple Juice Mass of vitamin C solution (ascorbic acid) = 0.250 g Volume of juice sample = 25 cm3 = 0.025 L ● Average volume of titrant used for Mott’s Apple Juice = (9.20 + 9.30 + 9.00) cm3 / 3 = 9.17 cm3 ● 14.60 cm3 iodine solution / 0.250 g vitamin C = 9.17 cm3 iodine solution / X cm3 vitamin C ⇒ (0.250 g * 9.17 cm3 ) / 14.60 cm3= 0.16 g vitamin C in that sample ● Concentration of vitamin C in Mott’s Apple Juice = mass of vitamin C (solute) [g] / volume of juice (solution) [L] = 0.16 g / 0.025 L = 6.40 g/L ● The % DV (daily value) for a nutrient is calculated by: dividing the amount of a nutrient in a serving size by its daily value, then multiplying that number by 100. Mott's Apple Juice has x mg of vitamin C. The RDA (Recommended Daily Allowance) or daily value for vitamin C put forward by the Food and Nutrition Board of the National Research Council is 60 mg/day for adults. The %DV of vitamin C in Mott's Apple Juice is 120%, then the amount of vitamin C per serving (0.24 L) is: (x mg of vit. C/ 60 mg) * 100 = 120 ⇒ x = 72 mg vitamin C per serving (0.24 L) If 0.24 L contains 72 mg of vit. C, then 0.025 L contains X mg of vit. C X = 7.5 mg = 0.0075 g ⇒ 0.0075 g vit. C is expected to be in 0.025 L of the juice sample based on the bottle label.

For Bag Drink ● Average volume of titrant used for bag drink = 0.60 + 0.50 + 0.50) cm3 / 3 = 0.53 cm3 ● (0.250 g * 0 .53 cm3 ) / 14.60 cm3= 0.009 g vitamin C in that sample ● Concentration of vitamin C in bag drink = 0.009 g / 0.025 L = 0.36 g/L For Welch's White Grape Juice ● Average volume of titrant used for Welch’s White Grape Juice = (1.80 + 1.90 + 1.80) cm3 / 3 = 1.83 cm3 ● (0.250 g * 1.83 cm3 ) / 14.60 cm3 = 0.0313 g vitamin C in that sample ● Concentration of vitamin C in Welch’s White Grape Juice = 0.0313 g / 0.025 L = 1.25 g/L For Ocean Spray White Cranberry Juice at Room Temperature ● Average volume of titrant used for white cranberry juice at room temperature = (1.30+1.30+1.20) cm3 / 3 = 1.27 cm3 ● (0.250 g * 1.27 cm3 ) / 14.60 cm3 = 0.0217 g vitamin C in that sample ● Concentration of vitamin C in Welch’s White Grape Juice = 0.0217 g / 0.025 L = 0.87 g/L ● The %DV of vitamin C in the white cranberry juice sample is  100%, then the amount of vitamin C per serving (0.24 L) is: (x mg of vit. C/ 60) * 100 = 100 ⇒ X = 60 mg vitamin C per serving (0.24 L ) If 0.24 L contains 60 mg of vit. C, then 0.025 L contains X mg of vit. C X = 6.2 mg = 0.0062 g ⇒ 0.0062 g vit. C is expected to be in 0.025 L of the juice sample based on the bottle label. For the Boiled Ocean Spray White Cranberry Juice ● Average volume of titrant used for the boiled white cranberry juice at room temperature = (0.40 + 0.20 + 0.50) cm3 / 3 = 0.37 cm3 ● (0.250 g * 0.30 cm3 ) / 14.60  cm3= 0.00513 g vitamin C in that sample

● Concentration of vitamin C in the boiled white cranberry juice = 0.00513 g / 0.025 L = 0.20 g/L

Discussion The measured volume used in the standardization of the iodine solution (0.0146 L) was accurate as the difference between it and the theoretical value of 0.0227 L was 0.0081 L. From the experiment, 0.16 g of vitamin V was found to be in the apple juice sample which was only 0.15 g higher than the expected value from the bottle label of 0.0075 g. The very low vitamin C concentration measured in the bag drink (0.36 g/L) indicated that it might not have contained enough natural fruits that would have been the main source of the vitamin C compared to the white grape juice that had a much higher concentration of 1.25 g/L At room temperature, the the boiled white cranberry juice sample was found to have vitamin C concentration of 0.0217 g which was only 0.015 g higher than the expected value from the bottle label of 0.0062 g. In addition, this vitamin C concentration was 0.67 g/L higher than that of the boiled white cranberry juice. These two vitamin C content values differ significantly as over 70% of the vitamin c has been lost after boiling. Vitamin C is the very unstable and heat sensitive vitamin. Boiling involves high heat which denatures the vitamin C, This resulted in a much lower concentration in the juice sample after high heat exposure.

Figure 1: Chart of the Vitamin C Concentration of Various Juice Samples Ranked From Highest to Least Concentrated

References Helmenstine, A. (2018, September 27). Vitamin C Determination by Iodine Titration. Retrieved November 3, 2018, from https://www.thoughtco.com/vitamin-c-determination-by-iodine-titration-606322 Igwemmar, N., Kolawole, S., & Imran, I. (2013, November 11). Effect Of Heating On Vitamin C Content Of Some Selected Vegetables. Retrieved November 3, 2018, from http://www.ijstr.org/final-print/nov2013/Effect-Of-Heating-On-Vitamin-C-Content-Of-S ome-Selected-Vegetables.pdf Zeratsky, K. (2016, July 15). What do the Daily Value numbers mean on food labels? Retrieved November 3, 2018, from https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers /food-and-nutrition/faq-20058436...