C2.1 - Separation techniques - Flashcards
Filtration equipment
Filter paper, funnel, residue, conical flask, filtrate
How does filtration work
- filtration separates an insoluble substance in the solid state from substances in the liquid state
- it works because filter paper has tiny, microscopic holes
- when you filter a mixture of sand and water, water molecules are small enough to pass through the filter paper, but the larger grains of insoluble sand cannot
- the sand stays behind in the filter paper as the residue while the water passes through as the filtrate
- particles of a dissolved solute are also small enough to pass through filter paper
3 things that could happen when heating solution
- if you heat a solution, the solvent evaporates leaving the solute behind
- if you heat the solution too strongly, you get a powder
- if you allow the solvent to evaporate slowly, you get regularly shaped crystals
How crystallisation works
- heat the solution until it becomes a saturated solution
— - a solution is saturated when no more solute can be dissolved at that temperature - crystals will start forming at this point, so let the solution cool slowly
- as the solution cools, the solubility of the solute decreases, so more crystals form
- separate them from the remaining solution by filtration, and dry them in a warm oven or by patting them with filter paper
What simple distillation does (simple)
Separates a solvent from a solution
How simple distillation works
- it relies on the solvent having a much lower boiling point than the solute
- when the solution is heated, the solvent boils but the solute does not
- the solvent escapes from the solution in its gas state
- it is then cooled and condensed back to its liquid state by a condenser, a piece of apparatus that is kept cold using a flow of cold water
Tap water contains dissolved salts.
What happens during simple distraction of tap water.
- water vapour escapes from the tap water, leaving the dissolved salts behind
What fractional distillation does (simply)
Separates two or more substances from a mixture in the liquid state
What fractional distillation relies on and uses
- it relies on each substance having a different point and uses a piece of equipment called a fractionating column
During fractional distillation of an ethanol-water mixture, ethanol vapour and water vapour both leave the liquid mixture.
In the fracturing column: (3)
In the condenser: (2)
In the FC:
- the vapours condense on the inside surface, heating it up
- when the temperature reaches the BP, ethanol vapour cannot condense any more, but water vapour can
- water droplets fall back into the flaks, and ethanol vapour passes into the condenser
In the C, the ethanol vapour is cooled and condensed back to its liquid state.
It drips into the collecting container.
Each substance separated by fractional distillation is called? + why
- a fraction
- because it is just part of the original mixture
Importance of the fractionating column (1)
And its features (1)
And what happens (1)
- you could carry out fractional distillation without the fractionating column
- however, the fractionating column improves the separation of the mixture
- it has a large SA on which the vapours can continually condense
- during fractional d. , the column becomes hottest at the bottom and coolest at the top
Chromatography relies on 2 different chemical phases
Stationary phase - does not move
Mobile phase - does move
A phase is?
A substance in the solid, liquid, or gas state
Phases in paper chromatography ?
Stationary = absorbent paper Mobile = a solvent in the liquid state, such as water or propanone
Thin layer chromatography - phases
stationary = thin layer of of silica or alumina powder spread over a plate of glass or plastic
Thing layer chromatogram to separate a sample into its components for identification of analysis: (steps)
1 - put the solvent into a chromatography tank to a depth of about 1cm. If the solvent is flammable, make sure that there are no naked flames, and that the room is well ventilated.
2 - add a small amount of the sample to the baseline, taking care not to damage the powder on the plate
3 - let the solvent travel through the powder, and take the plate out before it reaches the top
4 - analyse the pattern of coloured spots, which is called a chromatogram
Tell me about the pattern produced in TLC (3)
- The pattern produced depends on how each component is distributed between the two phases
- a component travels further up the plate if it forms stronger bonds with the mobile phase than with the stationary phase
- a component will not travel very far if it forms stronger bonds with the stationary phase than with the mobile phase
What scientists use to compare spots on a chromatogram - and what this means - and what is it
- scientists use Rf values to compare spots on a chromatogram
- if two spots have the same Rf value and are the same colour, they are likely to be identical
Distance travelled by substance / distance travelled by solvent
Rf values - range ? Units?
Vary from 0 to 1
Have no units
Gas chromatography - phases
Stationary = silica or alumina powder packed into a metal column
Mobile = unreactive carrier gas such as nitrogen, which does jot react with the sample
What (2) does gas chromatography do?
- separates the components of a mixture, and also measures their amounts
How gas chromatography works - 5
- the sample is turned into the gas state when it is injected into the column
- the carrier gas pushes the sample through the column
- the different components take different times to travel through the column, depending on how strongly they bond to the stationary phase
- a detector sends a signal to a computer as each component leaves the column
- the computer produces a chromatogram in which each component is a peak plotted against the travel time
How to tell if a substance is pure?
Use paper or thin-layer chromatography
