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
What is the maximum Rf value to be had?
1.0
What is TLC - thin layer chromatography used for in the real world? Give examples
To determine amino acids in blood samples or analyse food dyes
What is gas chromatography?
It identifies the percentage and number of compounds or impurities present in a sample
Describe gas chromatography
The mobile phase is a gas- it’s carried out in a column which contains the stationary phase. The sample is injected into the column
The retention time for each component is identified- this is the time it takes for the component to pass from the column inlet to the detector
The retention time is compared to standard compounds to identify an unknown substance.
The peak area also gives the approximate percentage composition of the mixture - peak area is proportional to the amount of substance
What is high performance (pressure) liquid chromatography
This uses a solid stationary phase within a column. The mobile phase is a liquid and is passed through the column.
The retention time for each component can be identified
Retention time is then compared to standard compounds to identify the Unknown substance
The peak area also gives the approximate % composition of a mixture- area under peak is proportional to amount of substance
Can be used to isolate and purify compounds and determine the conc of a compound
What is HIGH PERFORMANCE (pressure) LIQUID CHROMATOGRAPHY USED FOR
Can be used to isolate and purify compounds and determine the conc of a compound
How can the retention time for each component be used to identify Unknown substances (in HPLC AND GAS)
Compare retention times to standard compounds to identify an unknown substance
Define gas chromatography
Identify number or percentage of compounds or impurities within a sample
Method for gas chromatography? 3 marks
1- the mobile phase is a gas, carried out in a column which contains stationary phase
2- he sample is injected into the column and retention time is taken for each component (retention time is the time taken for each component to pas from the column inlet to the detector)
3- retention time is compared to standard compounds to identify the unknown
Define high performance liquid chromatography?
Used to isolate or purify a compound or determine its concentration
Method of high performance liquid choromatography
1- uses a solid stationary phase in a Column, mobile phase is a liquid and is passed through this
2- retention time taken and compared to standard compounds to identify the Unknown
What does the peak area tell us in gas chromatography and high performance liquid?
The amount of substance (peak area proportional to amount of substance)
Define chromatography in general
Separation technique: separates components in a mixture between the stationary and mobile phase
How would you identify a compound using MPS?
Small sample is mixed with a known pure sample
If they’re identical, MPS stay the same
If they’re different, one will behave as an impurity and lower the MP and it will lose its sharpness
Pure compound MP
Sharp. With a a range of 1 or 2 degrees
impure compound MP
MP over a range
Define chromatography
Separated components in a mixture between the stationary and mobile phase
How can you obtain a pure dry sample of a carboxylic acid?
Add dilute acid
Filter and dry
How do you isolate a product?
Filter product
Wash with cold solvent
recrystallise from hot water
Dry crystals in an oven just below MP
