Purity and Purification of Solids - Recrystallization

Purity and Purification of Solids- Recrystallization

Marissa Christenson

CH 337 Laboratory, Section 006

Department of Chemistry

Portland State University, Portland OR

Abstract

We separated and purified two samples of adipic acid. In the first sample we separated and recrystallized without decolorization and in the second sample we separated and recrystallized with decolorization using charcoal. The recrystallization solvent chosen was water due to the similar polarities of water and adipic acid. Lastly, we took our purified samples and found the boiling point of the first sample to be _____ and the boiling point of the second sample to be _____ , and then we compared these to the known boiling point of adipic acid. The boiling pints were _________________________________________________________________.

Introduction

Crystallization is important when it comes to the purification of solid organic compounds. Recrystallization techniques include dissolving the solid material in the least amount of hot solvent, saturating the solvent with solute, which then precipitates from the solution as crystals when the solution cools. The solvent that is chosen must have similar characteristics, such as polarity, to the solute trying to be purified. The goal is to obtain the maximum amount of the purest crystals to form. In order to do so, the impurities must be in low concentrations in comparison to the desired substance. Once crystallized, the desired solid can be collected via vacuum filtration, washed with cold water, and dried. If you are dealing with a color impurity, small amounts of charcoal are used to absorb the color impurity; it is then removed by filtration from the solution. Finding the crystallized products boiling point and comparing it to the boiling point of the pure substance can help clarify to what degree of purity the solid product is. This process is based on the idea that the solubility of a compound in a solvent increases with temperature.

Experimental Section:

The procedures for this lab are found in the PSU lab manual1 and the pure and impure adipic acid used were from the PSU Chemistry Stockroom. Obtain a 1 gram sample of impure adipic acid and put it into a 50mL flask. Use water as the solvent and add approximately 2mL of it as well as a magnetic stir bar to the flask. Place the flask on a hot plate/stirrer and bring it to a boil. Heat a 50mL beaker with some water as well. Add little water at a time as needed to dissolve the entire solid. Now that the solution is saturated, filter it by pouring it through fluted filter paper in a preheated stemless funnel and into a second 50 mL Erlenmeyer flask. Use the