The Purity and Purification of Solids Recrystallization Lab

The Purity and Purification of Solids
Recrystallization

ABSTRACT
In this experiment, impure adipic acid is purified though recrystallization. The impure adipic acid is dissolved in a solvent. After cooling it is ran through a vacuum filter to separate any moisture. The dry crystals are then weight for percent yield and the melting point range is taken to test the purity. There were two different trials ran in this experiment. The difference between the two was the addition of charcoal in the initial step to remove color impurities. For part A (without charcoal) the initial impure weight was 1.0256g. After the filtration, the final pure product weighted 0.6063g which is a 59.17% yield. The Melting point range for part A was 151.1°C – 154.9°C. For part B (With charcoal) the initial weight was 1.0008g. After filtration the pure crystals weighted 0.4631g. This came out to be a 46.27% yield. The melting point for part B is also 153.0°C – 156.8°C.
INTRODUCTION
Recrystallization is a method that is used to purify solids. To have a good test, two criteria must be met. A high degree of purity is achieved after the purification and there must be a maximum recovery of the sample. This technique of purification is only effective when there is a smaller amount of impurity in one substantial component.
EXPERIMENTAL SECTION Material
Impure adipic acid charcoal water
Erlenmeyer flask filter paper Heat plate
Filter flask 50ml & 250ml Beakers O ring & stand
Graduated cylinder Pipette Ice
Scoop Stemless funnel Vacuum filter (assembled)
Spatula Boiling chips Scale
Weighing paper Holding strap Hirsch funnel
Capillaries Spot tray Mel temp device Procedure
Part A – recrystallization without decolorization (no charcoal).
Weight out approximately 1.0g of impure adipic acid and get 2 boiling chips from jar. Add the adipic acid and boiling chips to a 50ml Erlenmeyer flask with about 6ml of water to create

References: Organic Chemistry Laboratory I, CH 337M; Department of Chemistry, Portland State University: Portland OR; p 1 Lab Two Question 1. 2. Recrystallization is generally not an effective purification method for a solid which is highly impure because the impure component could recrystallize in the cooling process. The reason why it works when there are smaller amounts of impurities is because a small amount of impurities are dissolved in a larger amount of liquid. When the main component recrystallizes the impurities stay dissolved in the liquid because it is at the point of its solubility. If there was a larger amount of impurities it would give itself a chance to recrystallize. 3. A – It might be advantageous to chill the mixture in an ice bath before suction because the pure major component separates as crystals under lower temperatures. If the temperature is room temperature or higher, the major component will dissolve and not form crystals. B – This same ice bath could be detrimental if the original sample contained a high proportion of impurities. There would be a higher chance of the impurities also recrystallizing under cooler temperatures. The final product might contain both pure and impure substance. 4. A – Compound A has a solubility of 7.03g per 10 mL at 100°C. It would take 23.61mL of boiling water to dissolve 16.6g of compound A. B – 0.6847g of compound A would crystalize from the 16.6g at 23°C 5. If we repeated the experiment in Mexico City at an elevation of 7700 ft about sea level. It would take much more boiling ethanol to dissolve the same amount. The temperature of boiling ethanol would decrease at a higher elevation. So what would be 100°C at sea level might only be 80°C at 7700 ft above sea level. Therefore it would need more ethanol to be soluble. If there is enough ethanol to be soluble, I don’t think that there would be a change in the recovery amount if they are both chilled to the same temperature. The recovery amount would stay the same.