This experiment consists of two parts. In the first portion of the experiment, the students will be standardizing the base. In the second part of the experiment, the students will use the base, which was previously standardized to titrate vitamin C, which contains ascorbic acid. The percentage of ascorbic acid in the vitamin C sample will then be determined.

EQUIPMENT

* Two 50 mL burettes

* Three 250 mL Erlenmeyer flasks

* Balance

* 10, 50 and 250 mL graduated cylinders

* Storage container

* Stirring rod

CHEMICALS

* Oxalic Acid

* Milk of magnesia

* Phenolphthalein indicator

* Distilled water

* Vitamin C

PART I: Standardization of Milk of Magnesia

Weigh out 1.5 g of oxalic acid and place it into a volumetric flask and then dilute to 100 mL with distilled water. Dispense 20 mL of this solution into an Erlenmeyer flask and add 3 drops of phenolphthalein indicator to the flask. Prepare a solution of milk of magnesia by diluting 17 mL to 200 mL using distilled water. Titrate the 20 mL oxalic acid sample with the milk of magnesia solution to the end point.

After completing three titrations of oxalic acid samples, calculate the average molarity of the milk of magnesia solution.

PART II: Determination of the Percent of Ascorbic Acid in Vitamin C

Weigh 2 100 mg tablets of vitamin C. These tablets are then to be crushed and dissolved in 100 mL of distilled water. Take 7 mL of the milk of magnesia solution previously prepared and dilute to 100 mL with distilled water. Fill a clean 50 mL burette with this solution. Dispense 20 mL of the vitamin C solution into a 250 mL Erlenmeyer flask and add 3 drops of phenolphthalein indicator. Titrate the milk of magnesia sample with the vitamin C solution.

After completing three titrations of the milk of magnesia sample, calculate the average molarity of the vitamin C sample and then determined the percentage of ascorbic acid in the vitamin C sample.

by http://www.chem.umd.edu