Lab 3: OCHEM 1
Recrystallization **** process of purifying an impure crystalline solid via heating in a suitable solvent, followed by cooling to allow the solid to reform in such a way that the impurities are excluded from the purified solid.
Gravity Filtration
Recrystallization **** process of purifying an impure crystalline solid via heating in a
suitable solvent, followed by cooling to allow the solid to reform in such a way that the
impurities are excluded from the purified solid.
Gravity Filtration **** process of removing insoluble impurities from recrystallization
solution
Suction Filtration **** process of isolating pure solid from liquid filtrate using a vacuum
Suitable solvent properties **** 1. Chemically inert.
2. Compound solubility is temperature dependent.
3. Solvent boiling point < melting point of compound.
4. Impurities soluble at all temperatures or insoluble at all temperatures
5. Sufficiently volatile to remove.
Step 1: Choosing the Right Solvent **** 1. If the solvent does not dissolve at room
temperature.
2. If it dissolves with heat.
3. If it crystallizes with an ice-water bath.
Bad Solvents **** 1. Dissolving at room temperature
2. If it does not dissolve with heat.
3. If it does not crystallize.
Step 2: Dissolving the Compound **** 1. Heat solvent (95% ethanol in H2O) to gentle
boil.
2. Place unknown mixture in flask
3. Add hot solvent
4. Swirl
5. Use hot plate to keep solution warm.
6. Repeat 1-3 until all dissolved or until no additional material dissolves.
What is the purpose of hot filtration? **** A hot filtration is used to remove insoluble
impurities.
How to filter hot solution? **** 1. Use a stemless funnel.
2. Fluted filter paper
3. Heated receiver vessel.
-wash filter paper with additional hot solvent.
In gravity hot filtration, keep the solution from cooling too much as this can lead to... ****
premature crystal formation and potential product loss.
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