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 vinegar, which contains acetic acid. The percentage of acetic acid in the vinegar 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

* Tartaric acid

* Milk of magnesia

* White vinegar

* Phenolphthalein indicator

* Distilled water

PART I: Standardization of Milk of Magnesia

Prepare a solution of milk of magnesia by diluting 7 mL to 140 mL using distilled water. Place 20 mL of this milk of magnesia solution into a 250 Erlenmeyer flask and add 3 drops of phenolphthalein indicator to the flask.

Weigh out 1.3 g of tartaric acid * and place it into a volumetric flask and then dilute to 200 mL with distilled water. Fill a 50 mL burette with this tartaric acid solution. Titrate the 20 mL milk of magnesia sample with the tartaric acid solution to the end point. Tartaric acid will give a sharp endpoint that is very distinct and clear to recognize.

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

* The tartaric acid may be substituted with citric acid, oxalic acid or ascorbic acid.

PART II: Determination of Acetic Acid Content in a Vinegar Sample

Take 10 mL of a vinegar sample and dilute to 200 mL with distilled water. Fill a clean 50 mL burette with this solution. Fill a second burette with the milk of magnesia solution that was prepared in Part I of this experiment. Dispense 20 mL of the milk of magnesia solution into a 250 mL Erlenmeyer flask and add 3 drops of phenolphthalein indicator. Titrate the milk of magnesia sample with the vinegar.

After completing three titrations of the milk of magnesia sample, calculate the average molarity of the vinegar and then determined the percentage of acetic acid in the vinegar sample when it is given that the density of the vinegar solution is 1.00 g/mL.

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