Crystallization is a method of ______________ by focusing on their _____________
purifying crude solids
solubility
What are the steps in Macro-scale Crystallization (greater than 0.1 gram)
1. Dissolving the solid
2. Removing insoluble impurities
3. Crystallizing
4. Collecting and Drying
When choosing a solvent for re-crystallization, what should we look for?
1. A solvent in which the compound has high solubility in high temperatures but low solubility in cold solvent.
2. A solvent whose BP is lower than the compounds MP
3. Should have different solubility for the compound and the impurities
4. Should be cheap
Does solubility of most organic solids increase with temperature or decrease
Solubility of organic solids increases with temperature
Theory of Crystallization
1. The compound to be purified should:
2. The Impurity should:
1. The compound should have mod or high solubility in hot solvent and low solubility in cold solvent
2. The impurity should be insoluble in hot solvent or high soluble in sold solvent, easily removed after crystallization, should not be reactive with comp
True or False
In order to minimize the loss of material in the mother liquor, it is desirable to dissolve the solid in the greatest amount of cold solvent possible
False!!! Use a minimum amount of near boiling solvent should be used.
In the experiment, how do you remove insoluble impurities?
by using a fluted filter paper and performing gravitational filtration, the hot solution is filtered. The insoluble impurities and charcoal will remain in the filter while solvent and dissolved desired compound will remain in solution
What are the steps to re-crystallizing the compound
1. Place solution in an Erlenmeyer flask
2. Allow to cool to RT
3. Place in ice bath and allow to slowly cool, undisturbed to allow for maximum quality and purity
How can crystallization be induced?
1. Scratching the inside surfers of flask vigorously with a glass rod
2. Addition of small amounts of original material, which is called seeding
3. If too much solvent was added, some should be evaporated off by heating and following re-crystallizing
Once you observe crystals forming in the erlenmeyer flask, how do you separate them from the solvent?
by vacuum filtration using a Buchner funnel (Place filter paper in the buchner funnel and wet it with a small amount of cold solvent
How can you tell is the crystallization was successful and your compound no longer has impurties?
Test the MP, now add 1:1 ratio of compound plus lab reference and if the MP doesn't change, purification was successful