Separation of Chemical Compounds Flashcards
What are the different separation techniques?
- Filtration
- Distillation
- Recrystallisation
- Chromatography
What is filtration and what are the two types?
Filtration is the separation of solid from liquid
- Gravity Filtration
- Vacuum Filtration
What is Distillation?
The separation of liquids with varying boiling points
What is recrystallisation?
The removal of impurities from solids
What is the process of gravity filtration?
- The mixture of solid and liquid is passed through porous material (usually filter paper)
- The solid is trapped on the porous material whilst the liquid passes through
- Filtration is usually done by using gravity filtration and fluted filter paper
Why is fluted filter paper used?
Gives a higher surface area
When is gravity filtration used?
For smaller volumes of mixture
How is a vacuum filtration set up ?
- Secure the Büchner flask with the clamp and stand
- Attach the vacuum to the flask
- Place a stopper in the flask and attach the Büchner funnel
- Add the filter paper on top of the porous plate and wet it with the solvent
- The filter paper should cover all the holes but not lift on the sides
- Turn the vacuum on slowly
- Turn the vacuum on higher to speed up the filtration but gently so the filter paper doesn’t rip
How does filtration work?
The components of the mixture are in different states (solid and liquid)
How is distillation set up?
- Secure the flask with a clamp and stand
- Attach the condenser with cold water coming in from the bottom and out the top
- Place the collecting flask at the end of the condenser
What is the process of distillation?
- Add the mixture (e.g. salt water) and boiling chips (anti-bumping granules) and thermometer till where the condenser is attached
- Place the Bunsen burner under the round bottom flask
- The mixture will be boiled and produce vapour/steam that rises to the condenser and thermometer
- The cold water surrounding the condenser will cool the steam in the condenser and will convert the gas back into liquid
- The distillate will be collected in the flask
Where should the thermometer sit and why?
The thermometer should sit by the condenser tunnel NOT IN THE LIQUID
Because we are measuring the temperature of the steam (condensed distillate)
Why should the distillation flask be no more than half full?
The unwanted substance may make it’s way to the distillate
Why should the heat source be easily removable?
Because the mixture may begin to boil violently
Why does distillation work?
Because the boiling points of each component are different
What are the two types of impurities?
- Insoluble material - Anti bumping granules etc..
- Small volumes of unreacted chemicals
What is the process of recrystallisation?
- Dissolve the impure crystals in the smallest volume possible of hot solvent
- The solvent choice is important because the desired product must be soluble in the solvent when it’s hot and insoluble in the solvent when it’s cold
- Hot filtration with suction (vacuum filtration with the hot dissolved mixture) to remove the non-soluble impurities
- Allow the crystals to reform
- Cold filtration under gravity (gravity filtration with the crystals and distilled water) to remove soluble impurities
- Dry the pure crystals
What are the two phases in chromatography?
- Stationary phase - The TLC plate or chromatography paper (whatever the compounds will be travelling through/on)
- Mobile phase - The solvent
What is the relationship between the chemical and stationary phase when the chemical that moves the least?
The chemical reacts the strongest with the stationary phase
What is the relationship between the chemical and stationary phase when the chemical that moves the most?
The chemical reacts the weakest with the stationary phase
Why is the TLC plate useful in chromatography?
The TLC plate uses silica bonded to a flat sheet of aluminium
- Silica is very polar because of the -OH groups, therefore it can make hydrogen bonds with the components in the mixture
What is the process of regular chromatography?
- Draw a line in pencil on the TLC plate about 1cm away from the bottom (this is the stationary phase)
- Prepare a beaker with less than 1cm of solvent (this is the mobile phase)
- Place a dot of the sample onto the pencil line and place the TLC plate into the beaker
- The solvent will travel up the TLC plate this is known as the solvent front, mark this with pencil and the sample dot will have travelled too
- Calculate the Rf values and compare the values of the unknown components to the known components
How is the Rf value calculated?
Rf = Distance travelled by the compound/ Distance travelled by the solvent
How does chromatography work?
The dissolved chemicals interact with the stationary phase differently
