Putification And Separation Flashcards
Distillation simple
Separates miscible liquids because some liquids are soluble in water- only works if liquids have different BPS
- mixture of both heated to produce hot vapours
- cold water enters condenser at lower end and leaves at higher
- hot vapours rise and enter condenser, then cool condense and run into the beaker as a liquid
- the lower BP boils first and vapours initially contain this, the higher BP remained behind in flask as a liquid
Fractional distillation
Same as simple distillation except a fractioning column is placed between the boiling flask and condenser- fitted with beads, beads improve the separation between the liquids being distilled
Steam distillation
Used to remove high BP liquids from the reaction mixture- used for compounds that may decompose near their BPS- the liquid forms an insoluble layer with the condensed steam in the collecting flask. Separating funnel is then used to separate the 2 liquids
Distillation under reduced pressure
If compounds decompose at temps near their BPs then they should be distilled under reduced pressure. this means they’ll boil at lower temps, distillation apparatus is attached to vacuum pump which reduces pressure
When should distillation under reduced pressure be used?
When miscible liquids are selected from Escher and the compounds decompose at temps near their boiling points .
Separation of immiscible liquids
Sepeation done using a separation funnel.
Funnel used to carry out a solvent extraction- this is the separation of a substance from one liquid into another. It must be immiscible and substance must be more soluble in one of the liquids
What do you need in order for the separationof immiscible liquids?
Immiscible liquids
A substance must be more soluble in one of the liquids
what is filtration
Removal of insoluble solids from liquids- involves a filter funnel and filter pummel which is fluted (folded)- a Büchner funnel is normally attached to a vacuum pump via a splash back flask- called vacuum filtration
What are the melting pints of pure and impure compounds?
Pure: sharp MPS over a range of 1-2 degrees - this sharp MP can be used to eliminate many other compounds
Impure: melt over larger range
Mixed MPS
If the identity of s compound is suspected, a small sample is mixed with a. Known pure sample.
If the 2 are identical- there will be no change in the MP value
If no, then one behaves as an impurity and the MP may be lowered and lose its sharpness
Recrystallisation
- what it’s used for
- description
To purify solids - a solvent is found which will dissolve both the compound and impurities when hot but dissolves much less of the compound when cold
Method:
- find suitable solvent via looking at literature
- dissolve sample in the minimum volume of hot solvent
- filter hot (if necessary) to remove impurities, allow to cool and filter
- wash sample with cold solvent and dry below MP
This is necessary before weighing in order to give accurate yield of a pure product
What is chromatography and what is its limitations?
Separates components in a mixture between a mobile phase and a stationary phase
Limitations:
1-similar compounds have similar Rf values or retention times
2-Unknown compounds have no reference Rf values or retention times for comparison
Thin layer chromatography
The stationary phase is a thin layer of silica gel- spread over the surface of a thin glass plate.
A small dot of sample solution is placed at the bottom of the plate
Then placed in a . Jar containing shallow layer of solvent and is sealed
Each dot is just above the solvent. The solvent is in its mobile phase and rises up the plate. The more soluble the solvent the further it travels
The retardation factor for each component can be calculated via-
Rf= distance moved by component / distance moved by solvent
How do you calculate retardation value on TLC?
Rf= distance moved by component / distance moved by solvent
How can identification of an unknown substance be done from a Rf value?
By comparing the Rf value to standard compounds- this identifies the unknown substance
