The major ingredient in commercial vitamin C is ascorbic acid (H2C6H6O27, Mr = 176.12). It is acidic — Physical Chemistry — Kinetics Chemistry Question

The major ingredient in commercial vitamin C is ascorbic acid (H₂C₆H₆O₂₇, Mr = 176.12). It is acidic and a reductant, therefore, both acid–base and redox titrations can be used to measure the amount of ascorbic acid in commercial vitamin C tablets. This experiment has two parts, the first part involves using an acid–base titration to determine the amount of ascribed acid in a vitamin C tablet. The second part involves using a redox titration to perform a similar determination. The evaluation is based on accuracy. The acid–base titration accounts for 30 %; the redox titration 60 %; and a comparison of these two methods 10 % of the final score.

CHECK REAGENTS AND APPARATUS BEFORE YOU START

Reagents
NaOH solution, (concentration is shown on the label)
Thiosulfate (Na₂S₂O₃) solution, (concentration is shown on the label )
Iodine solution (0.01 mol dm –3)
Indicators:
Phenolphthalein solution
Methyl Red solution
Starch solution

Apparatus
Spatula 1
graduated cylinder, 10 cm 3 1
graduated cylinder, 100 cm 3 1
funnel 1
pipette, 20 cm 3 1
safety bulb 1
Pasteur pipettes (dropper) 6
brush 1
beakers, 100 cm 3 2
beakers, 250 cm 3 2
Erlenmeyer flasks, 125 cm 3 , 4
Erlenmeyer flasks, 250 cm 3 2
filter papers 10
weighing papers 10
mold and pastel, 1 set
burettes (1 rack) 2
burette brush 1
volumetric flask, 100 cm 3 1

Procedure
Preparation of the ascorbic acid solution
Dissolve the vitamin C tablet in water; filter if necessary. The final volume of the solution should be 100 cm 3.

1. Acid–Base Titration
1 a Pipette 10 cm 3 of the above solution into an Erlenmeyer flask. Choose the appropriate indicator to perform titration.
1 b Repeat step 1a a total of 3 times.
[VISUAL]

Part 2: Determination of the concentration of the provided iodine solution using the standardized thiosulfate solution.
2 a Pipette 20 cm 3 of the iodine solution into an Erlenmeyer flask, and titrate by using standard Na₂S₂O₃ solution. Use starch as the indicator.
2 b Repeat step 2a a total of 3 times.
[VISUAL]

Part 3 Determination of the amount of ascorbic acid
3 a Pipette 10 cm 3 of the solution from step 1 into an Erlenmeyer flask. Add a few drops of starch as indicator and titrate with the iodine solution.
3 b Repeat step 3a a total of 3 times.
[VISUAL]