Purity and Purification of Solids -- Recrystallization

EXPERIMENT #2:

THE PURITY AND PURIFICATION OF SOLIDS--

RECRYSTALLIZATION

Created by

Phaedra Malmquist

October 15, 2012

CH 337-Sec 017

ABSTRACT

This experiment demonstrates how to carry out a proper recrystallization and analyze the products after the procedure. Recrystallization is a widely used method of purifying a substance through filtration and drying. The two samples of adipic acid used for this process underwent a hot filtration, were cooled, and then vacuum filtered. The unpurified sample retained the bluish color throughout the procedure and upon drying while the purified sample became a fine white powder.

The products from both experiments were weighed and their melting points were tested. 64.2% of the purified sample and 26.0% of the unpurified sample was recovered after completely drying. The pure sample showed a sharper melting point than the bluish product but both temperature ranges were very similar to the MP of the original adipic acid.

INTRODUCTION

Recrystallization is the most common method used in the purification of solids that are “substantially enriched in one component”1 and have a low concentration of an impurity. Different substances are soluble at different temperatures and most solids dissolve more rapidly in solvents at higher temperatures. DI (distilled water) was chosen as the solvent for this experiment due to the general rule of “like dissolves like”.1 It was also chosen because the difference in solubility of water and adipic acid at high temperatures and at room temperature guarantee that proper crystallization will take place.

This experiment involves the recrystallization of adipic acid, which contains colored impurities; and as such, activated charcoal must also be added to one of the sample mixtures of hot solvent and adipic acid until the solution swirls clear. The activated charcoal absorbs the color and aids in the purification of the sample.

EXPERIMENTAL SECTION

To carry out this experiment it is important to have all the materials set up and ready to use as they are necessary. Before preparing the samples the hot plate was turned on, an ice-bath was prepared, and a ring stand with iron-ring clamped on was set up with a stemless glass funnel placed on it to be supported during filtration. Two large and two small pieces of filter paper along with two watch glasses were weighed and set aside for later use with their weights recorded in Table I. The Hirsch funnel and filter flask