Chemistry 30 Lesson 2-07 Page 1© 2014 T. de Bruin

Chemistry 30 Lab – Titration Analysis of Vitamin C in Orange Juice

Vitamin C is vital to the production of collagen, and it also protects the fat-soluble vitamins A and E andfatty acids from oxidation (vitamin C is an antioxidant). Vitamin C is a weak acid (ascorbic acid) and isstable in weak acids. Bases, such as baking soda, destroy vitamin C. It is also easily oxidized in air andsensitive to heat and light. Since it is contained in the watery part of fruits and vegetables, it is easilylost during cooking in water. Loss is minimized when vegetables, such as broccoli, are steamed insteadof directly cooked in water. Any copper in the water or in the cookware will also diminish the vitamin Ccontent of foods, because copper binds to vitamin C. In this investigation, you will determine theconcentration of vitamin C (ascorbic acid) in a sample of orange juice.

Problem

What is the molar concentration of vitamin C in orange juice?

Materials

· Lab apron and safety glasses· 50 mL burette· 10 mL pipette and bulb· 250 mL Erlenmeyer flask

· Iodine (I2) standardized solution (0.0595 mol/L)· Orange juice· lab stand and burette clamp· starch indicator

Procedure

1. Set up titration equipment.

2. Obtain approximately 75 mL of iodine solution. Fill burette with iodine solution titrant.

3. Obtain approximately 60 mL of orange juice.

4. Pipette a 10.00 mL sample of orange juice into a clean Erlenmeyer flask and add 3 drops ofstarch indicator.

5. Record the initial burette reading (to 0.1 mL precision).

6. Titrate the orange juice sample with iodine until a single drop produces a permanent colourchange. The endpoint occurs when the indicator changes to blue; however, since the orangejuice is orange, the endpoint will appear as a greenish hue in the orange juice.

7. Record the final burette reading. (to 0.1 mL precision).

8. Repeat steps 4 through 7 until three consistent results are obtained.

9. Dispose of all solution into the sink. Make sure you react all leftover solution before disposal.

10. Clean up lab equipment.

11. Complete the analysis.

Chemistry 30 Lesson 2-07 Page 2© 2014 T. de Bruin

NAME:Chemistry 30 Lab – Titration Analysis of Vitamin C in Orange Juice

ObservationsTrial 1 Trial 2 Trial 3 Trial 4

Final burette reading(mL)

Initial burette reading(mL)

Volume iodinesolution

Used (mL)

Analysis (Show all work)1. Balance the following skeleton equation for the reaction of ascorbic acid with iodine.

C6H8O6 (aq) + I2 (aq) → C6H6O6 (aq) + I−1 (aq) (acidic)

2. Determine the concentration of ascorbic acid (vitamin C) in the orange juice.

Chemistry 30 Lesson 2-07 Page 3© 2014 T. de Bruin

Chemistry 30 lab - Determination of H2O2 (aq) concentration NAME:

Trial 1 Trial 2 Trial 3 Trial 4Final burette volume (mL)

Initial burette volume (mL)

Volume KMnO4 (aq) used (mL)

Analysis

Molar concentration of H2O2: ...........................mol/L

Percent concentration of H2O2: ........................ %· graph the data in table 1 on the reverse side to be able to convert mol/L into %· graph not used in mark rubric, so it can be done on a calculator.

Chemistry 30 Lesson 2-07 Page 4© 2014 T. de Bruin

You do not have to show your work. Either graph manually on this page or enter the data on yourgraphing calculator to determine percent concentration of H2O2.