CHAPT 2 : techniques in organic chem Flashcards Preview

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Flashcards in CHAPT 2 : techniques in organic chem Deck (12)
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Technique that involves the condensation of solvent vapour back into the reaction vessel


what is filtration and the three types of filtration

filtration removes insoluble solid materials from a solution
1. gravity/ simple filtration
2. hot gravity filtration ( used during recrystallisation )
3. suction (vacuum) filtration


common errors with filtration

gravity filtration: adding too much sample causes filtration to be very slow as it relies on gravity
hot gravity filtration: glassware is not hot causing premature crystallisation & blockage of funnel
suction filtration: not using cold solvent cauosing crystals to redissolve


purpose of recrystallisation

used to purify solid compounds


requirements of recrystallisation

- desired solid must be solid at room temp
- solvent must not react with the desired solid
- purified compound must be very soluble in hot and almost insoluble in cold solvents
- impurities must be very soluble in cold and insoluble in hot solvents


reasons & solutions why crystals are not forming

1. solution is not saturated
- boil the solvent away

2. solution is still very hot
- use ice bath
- scratching inner walls to help induce recrystallisation


what does boiling point depends on

strength of intermolecular forces ( hydrogen bonding> dipole-dipole forces> dispersion force)
carbon chain length ( as molar mass increase= dispersion force increases)
molecular surface area


2 main factors for liquid - liquid extraction

1. polarity - polar components will dissolve in the aqueous layer while non-polar components will dissolve in the organic layer
2. density- the greater the difference in density, the better the separation


which is polar and which is non polar in TLC

stationary phase is polar
mobile phase is non polar


how to find retention factor

diet moved by compound / dist of solvent front


what will happen if
- polarity of components increases
- polarity of solvent increases

- Rf value decreases
- Rf value increases


position of components :

most polar- bottom
least polar- top