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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1

Reflux

Technique that involves the condensation of solvent vapour back into the reaction vessel

2

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

3

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

4

purpose of recrystallisation

used to purify solid compounds

5

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

6

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

7

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

8

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

9

which is polar and which is non polar in TLC

stationary phase is polar
mobile phase is non polar

10

how to find retention factor

diet moved by compound / dist of solvent front

11

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

- Rf value decreases
- Rf value increases

12

position of components :

most polar- bottom
least polar- top