Required practical 10: Preparation of organic solids and liquids Flashcards
What is reflux
Why is it used in this reaction
The continuous boiling and condensing of a reaction mixture
It allows organic mixture to be heated without losing any reactants or products
Why are anti bumping granules added
To prevent vigorous boiling, by making small bubbles instead of large bubbles
When using a separating funnel to purify an organic liquid,
How does using sodium hydrogencarbonate work to wash it
. Put the distillate of impure product into a separating funnel
- Add Sodium Hydrogencarbonate solution, shake it and release pressure from the CO2 produced by opening bong at regular intervals
It works by removing acidic impurities by neutralisation so converts to H2O, CO2 and Na2SO4
When using a separating funnel to purify an organic liquid,
How does saturated sodium chloride solution work to wash it
Saturated sodium chloride solution – helps separate the organic layer from the aqueous layer
After washing it, how does separating funnel work to purify organic mixture
Why is drying agent added
- Allow layers to separate in funnel, and then open tap to discard the aqueous layer
- Run the organic liquid into a clean, dry conical flask and add 3 spatula loads of drying agent anhydrous sodium sulphate
Drying agent should be insoluble in the organic liquid and not react with the organic liquid.
Its purpose is to dry it
Carefully pour the liquid into the distillation flask
Distil to collect pure product
Why would calcium chloride be added
It is a drying agent that soaks up remaining water, so liquid will remain cloudy until all water is gone
How do impurities affect melting point of organic mixture
They lower it, so the melting point will be lower than data book value
Also, it will melt over a range of several degrees
How do you measure melting point of organic solid
. Use electronic melting point machine
. Or use a practical set up where capillary tube is strapped to thermometer immersed in heating oil
This heating oil must have higher boiling point than the samples melting point, and lower flammability
In both cases, some salt is added into capillary tube which is then heated up and heated slowly when near the boiling point
How do you determine purity of organic product
Compare the melting point with data book value
How do you measure boiling point to determine purity of organic mixture
Where should the thermometer be
Why is this not the most reliable
. Either set up distillation, or put boiling tube in heating oil bath
Thermometer shouldn’t be in the bath, it should be above it to measure temperature of saturated vapour
. Note down the pressure as changing pressure can change boiling point of liquid
. Not very reliable as several substances can have the same boiling point
What does saturated mean in this experiment
It means the maximum amount of solute can be dissolved in solvent to have a solution
How is recrystallisation used to make compound more pure
. Dissolve impure compound in the minimum volume of hot (almost boiling) solvent
. Filter solution through filter paper quickly
. Cool the filtered solution by inserting
beaker in ice
. Suction filtrate with a Buchner flask to
separate out crystals.
. Wash the crystals with distilled water.
. Dry the crystals between absorbent
paper.
What is the reasoning behind dissolving compound in hot solvent
Do this so it dissolves both the compound and its impurities when hot, but when cool it doesn’t dissolve organic compound
The minimum volume is used to get the
saturated solution and to enable
crystallisation on cooling.
This means that the desired compound is pure in crystals formed
Why do you put hot filter solution through filter paper quickly
This step removes any insoluble purities
And the heat will prevent crystals forming during filtration
Why do you cool filtered solution slowly by cooling in ice
. Doing it slowly will increase yield by ensuring all compound crystallises.
. Ice will increase yield of crystals forming
. This means crystals will form but soluble impurities will remain in solution form because they are only present in small quantities so solution isn’t saturated
