RP10- Preparation of a pure organic liquid

Question 1

what’s the general method for purifying an organic liquid

Answer 1

• put distillate of impure product into a separating funnel
• wash product by adding either :
  • sodium hydrogencarbonate solution , shaking and releasing the pressure from CO2 produced
  • Saturated sodium chloride solution
• allow the layers to separate in the funnel and then run and discard the aqueous layer
• run the organic layer into a clean dry conical flask and add three spatula loads of drying agent (e.g anhydrous sodium sulphate , calcium chloride ) to dry the organic liquid . When dry the organic liquid should appear clear
• Carefully decant the liquid into the distillation flask
• distilled to collect pure product

Question 2

why is sodium hydrogencarbonate used when washing the product

Answer 2

it will neutralise any remaining reactant acid

Question 3

why is sodium chloride added to wash the product

Answer 3

it will help separate the organic layer from the aqueous layer

Question 4

which is the organic layer

Answer 4

the layer with the lower and density - upper layer

Question 5

what should the drying agent be

Answer 5

insoluble in the organic liquid
not react with the organic liquid

Question 6

what’s the detailed method for preparing and purifying cyclohexene from cyclohexanol

Answer 6

• pour about 20cm3 of cyclohexanol into a weighed pear shaped flask . Reweigh flask and record mass of cyclohexanol
• using a plastic graduated dropping pipette , carefully and with frequent shaking , add to the flask approximately 8cm3 of conc phosphoric acid
• add a few antibumpint granules to flask and assemble the distillation apparatus so that the contents of flask may be distilled . Heat flask gently , distilling over any liquid which boils below 100 degrees
• pour distillate into a separating funnel and add 50cm3 of saturated sodium chloride solution , shake mixture and allow two layers to separate
• run off the lower layer into the beaker and then transfer the upper layer which contains the crude cyclohexene into a small conical flask
• add a few lumps of anhydrous calcium chloride or anhydrous sodium or magnesium sulfate to crude cyclohexene to remove water . Stopper the flask shake the contents and allow this to stand until liquid becomes clear
• decant liquid into a clean dry liquid weighed sample container
• re weight container calculate mass of dry cyclohexene produced

Question 7

what’s the detailed method for preparing and purifying an ester

Answer 7

1) propanol and ethanoic acid are mixed thoroughly in a round bottomed flask
2) conc sulfuric acid is added drop by drop to the mixture , and cooled in an ice water bath
3) when all acid has been added , a reflux condenser is fitted to the flask and mixture gently boiled over an electric heating mantle for about 30 mins
4) mixture is cooled and crude water is distilled off
5) distillate is placed in a repeating funnel and shaken with about half of its volume of 30% sodium carbonate solution with the pressure being released at intervals. The lower aqueous layer is then discarded
6) crude ester is shaken in a separating funnel with about half of its volume of calcium chloride solution which removed un reacted alcohol . Lower layer is discarded
7) ester is run into a clean dry flask containing some anhydrous calcium chloride and swirled
8) Ester is filtered into a clean dry flask with a few antibumping granules and distilled

Question 8

why is sulfuric acid used in preparing and purifying an ester

Answer 8

it’s a catalyst
it prevents uncontrolled boiling over add drop by drop and cool

Question 9

why is reflux used in preparing and purifying an ester

Answer 9

in reflux the reactant vapour of volatile compound are condensed and returned to the reaction mixture
Reaction is slow so its heater for 30 mins

Question 10

whys an electric heating mantle used in purifying and preparing an ester

Answer 10

allows for controlled heating and stops flammable vapour lighting

Question 11

whys sodium carbonate used in preparing and purifying an ester

Answer 11

it reacts with untreated acid and remaining catalyst still present after distillation

Question 12

why does the pressure of a gas need to be released in preparing and purifying an ester

Answer 12

reaction produced CO2 so pressure of gas needs to be released

Question 13

whys the upper layer organic in purifying and preparing an ester

Answer 13

because it has a lower density than water

Question 14

whys calcium chloride used in preparing and purifying an ester

Answer 14

calcium chloride is a drying agent
the liquid will appear clear when dry

Question 15

why are antibumping granules added to purifying and preparing an ester

Answer 15

to prevent vigourous , uneven boiling by making small bubbles form instead of large