RP 10 - organic

what is RP10

preparation of a pure organic solid, test of its purity, and preparation of a pure organic liquid

what is reflux

continuous boiling & condensing of a mixture

whens reflux used

to heat an organic mixture without losing reactants or products

purpose of anti bumping granuels

prevent vigorous or uneven boiling - by making small bubbles form instead of large ones

separating funnel purpose

to separate into two layers

1. higher density liquid (typically aqueous) = bottom layer

2. organic product layer = top layer

purifying organic liquid steps

1. put distillate of impure product in separating funnel

2. wash product

3. allow layers to separate, then run and discard aqueous layer

4. run organic liquid into conical flask

5. add 3 spatulas of drying agent

6. decant into distillation flask

7. distil to collect pure product

ways to wash the product (step 2)

1. sodium hydrogencarbonate solution, shaking and releasing pressure from CO2 produced - removes acid impurities by neutralisation

2. saturated NaCl solution - helps separate organic from aqueous layer

what should the drying agent be (step 5)

insoluble in the organic liquid and not react with it

what happens when the drying agent is added and examples

examples = anhydrous sodium sulphate, anhydrous calcium chloride

• absorbs remaining water

• liquid remains cloudy until all water drops have been removed

testing with melting point

pure = sharp, same as in quoted data books

impure = lower and melt over a range of degrees

measuring melting point ways

1. electronic melting point machine

2. practical set up - capillary tube strapped to a thermometer immersed in some heating oil

what happens in both cases

1. small amount of the salt put into capillary tube

2. heated up - slowly near melting point

3. compare experimentally determined value with one quoted in a data source

where can an error occur

if the temperature on the thermometer is not the same as the temperature in the sample tube

measuring boiling point to determine purity

1. distillation or boiling tube of sample in a heating oil bath

2. note pressure - changing pressure can change the boiling point

whys it not as accurate

several substances may have the same boiling point

how to get accurate measure of boiling point

thermometer should be above the level of the surface of the boiling liquid, and be measuring the temperature of the saturated vapour

recrystallisation method

1. dissolve impure compound in minimum volume of hot solvent

2. filter hot to remove insoluble purities

3. cool by inserting beaker in ice to recrystallise

4. suction filtrate with buchner flask to separate crystals

5. wash crystals with distilled water

6. dry crystals between absorbent paper

whats an appropriate solvent (step 1)

1. dissolve both compound and impurities when hot

2. compound itself does not dissolve when cold

why is the minimum volume added (step 2)

to obtain saturated solution, and enable crystallisation on cooling

what does both do

means the desired compound is pure in the crystals formed

what does hot filtering do (step 2)

1. removes insoluble impurities

2. the heat prevents crystals forming during filtration

whys it cooled (step 3)

to increase the yield by ensuring all of the compound crystallises

what does the water pump in a buchner flask do (step 4)

reduces pressure and speeds up filtration

why are the crystals washed with distilled water (step 5)

to remove soluble impurities

why is water removed (step 6)

it would affect % yield

buchner flask diagram

how is yield lost

1. crystals lost when filtering or washing

2. some product stays in solution after recrystallisation

3. other side reactions occurring