EXERCISE 2 Flashcards
(21 cards)
AKA 2-hydroxybenzoic acid which is odorless and white needle-like crystals used as an analgesic, antipyrectic, and anti-inflammatory.
Salicylic Acid
What purification technique utilizes the effect of temperature on solubility and the tendency of crystals to form definite lattice?
Recrystallization
What is the procedure of recrystallization?
- Crystal dissolution with appropriate solvent.
- Hot gravity filtration.
- Vacuum filtration.
- Crystal drying.
Characteristics of a good recrystallization solvent
- Slighty different polarity than the solute.
- Boiling point should be less than the melting point of desired substance.
- Relatively volatile.
- Desired substance must be soluble in solvent at high temperature and does not react with mere dissolution.
- Safe, non-toxic, inexpensive.
Purpose of minimum amount of solvent.
- Produces maximum amount of crystals.
- Recrystallization is easier on saturated or partially supersaturated solution.
Purpose of adding small amounts of activated carbon.
Adsorbs colored impurities.
Used to separate insoluble impurities from a hot solution, avoiding premature recrystallization of salicylic acid.
Hot Gravity Filtration
Purpose of using fluted filter paper.
- Higher surface of contact leads to faster filtration.
- Minimum contact with the walls of the funnel, avoiding premature recrystallization.
Purpose of stemless funnel.
Avoid premature recrystallation in a stemmed funnel.
Purpose of maintaining heat in the receiving container.
Maintain dissolved form.
Purpose of evaporating solvent to half its amount prior to cooling.
Ensures saturated or partially supersaturated solution for easier recrystallization.
Purpose of gradual cooling.
Prioritizes crystal growth over nucleation rate where large crystal lattice will have lesser impurities.
What to do if no crystals were formed?
- Scratch the sides of the container.
- Add a seed crystal.
What filtration uses a vacuum?
Suction Filtration
What is the goal of washing crystals?
Remove impurities in the recrystallized sample using a cold recrystallizing solvent.
Crystals washed with hot solvent leads to what?
Low recovery, no effect on purity.
Crystals washed with room temperature solvent leads to what?
High recovery, low yield.
This step is used for sample identification and index of purity.
Melting Point Determination
Why is pulverization done on watch glass instead of filter paper?
Due to lints on filter paper that may be incorporated as impurities.
Formula for % recovery.
(Mass of Recrystallized Sample / Mass of Crude Sample) x 100
Effect of loose, uneven packing of crystals.
Widens melting point range due to inefficient heat transfer among the sample.
