Organic Chemistry Lab Ii: Purity and Purification of Solids - Recrystallization

Organic Chemistry Lab II: Purity and Purification of

Solids - Recrystallization

Hagen Rainbow

Section 46

Abstract

In this lab we demonstrated how to carry out a proper recrystallization and how to analyze the products. We separated and purified two impure samples of adipic acid. In the first sample (Sample A) we separated and recrystallized without using a technique for removing the food coloring impurity, and in the second sample (Sample B), we separated and purified while using charcoal to remove the color impurity. We choose water as the recrystallization solvent because it has a similar polarity to adipic acid.

We found the melting point for both of the purified solvents was 154°C – 156°C. The color of the first sample was blue colored, while the second sample, treated with charcoal, was light blue and almost white. 27.0% of Sample A and 27.3% of Sample B was recovered after completely drying the purified samples. The purified samples showed a sharper melting point than the impure adipic acid.

Introduction

Recrystallization is a common method used to purify a solid substance that has a relatively low concentration of impurity. Recrystallization works by dissolving the solid material (solute) in the hot solvent, the pure substance then precipitates forming crystals when the solution is cooled. The solvent should have similar polarity and characteristics as the solute. Once the substance is crystallized, it can be vacuum filtrated and washed with cool water, then dried. If there is a color impurity, charcoal can be added to the hot solution in the beginning to absorb and remove the color. Comparing the melting point of the recrystallized sample with the impure sample or the known melting point of a pure sample can show how much the substance has been purified.

Experimental

In Part A, we dissolved 1.09g of adipic acid in 6mL of H2O then filtered the solution through a paper filter to remove impurities. We let the solution cool and form crystals, then vacuum filtered the solution to remove the purified adipic acid crystals. For part B, we dissolved 1.02g of adipic acid in 6mL of H2O then added charcoal to the hot solution to remove the color impurity. We then continued with the same recrystallization process as in part A. After sample A and B were dried, we took the melting points of both purified samples.

Results

Name Start Weight Purified weight % Recovery MP of Pure MP of Impure Appearance

Before/After Literature