Recrystallization is a purification technique used to purify solidcompounds. It is based on the principle that the solubility of a compound in a solvent increases with temperature, allowing impurities to be removed while the desired compound remains in solution at higher temperatures and then recrystallizes as the solution cools down.
Steps of Recrystallization:
Solvent Selection: Choose a solvent in which the compound to be purified has low solubility at low temperatures, but high solubility at high temperatures. The impurities should be either insoluble or very soluble in the chosen solvent.
Dissolving the Compound: Dissolve the crude compound in the minimum amount of hot solvent. This ensures that the compound is completely dissolved at an elevated temperature.
Impurity Removal: If there are insoluble impurities, they can be removed by hot filtration or through the use of gravityfiltration while the solution is still hot.
Recrystallization: Allow the solution to cool slowly, prompting the compound to recrystallize. The slower the cooling, the larger and purer the crystals will be.
Isolation of Crystals: The purified crystals are isolated by vacuum filtration, washed with a cold solvent to remove any remaining impurities, and then dried to yield the pure compound.
Recrystallization is a widely used method for purifying organic compounds in the laboratory due to its simplicity, effectiveness, and ability to yield high-purityproducts.
When studying recrystallization, it is important to understand the principles, steps, and factors affecting the process. Practice identifying suitable solvents for different compounds and understanding the mechanisms behind the purification technique. Additionally, familiarize yourself with the techniques for isolating and drying the purified crystals.
Energy - A. Energy is involved in all physical and chemical processes. It is conserved, and can be transformed from one form to another and into work. At the atomic and nuclear levels energy is not continuous but exists in discrete amounts. Energy and mass are related through Einstein's equation E=mc 2 . B. The properties of atomic nuclei are responsible for energy-related phenomena such as radioactivity, fission and fusion. C. Changes in entropy and energy that accompany chemical reactions influence reaction paths. Chemical reactions result in the release or absorption of energy. D. The theory of electromagnetism explains that electricity and magnetism are closely related. Electric charges are the source of electric fields. Moving charges generate magnetic fields. E. Waves are the propagation of a disturbance. They transport energy and momentum but do not transport matter.
Relate temperature to the average molecular kinetic energy.