Seperation techniques - topic 2 (pg 112-119) paper 1 Flashcards Preview

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solid state of matter

particle diagram - close together regular pattern of particles
movement of particles - vibrate about fixed positions
relative energy of particles - least stored energy


liquid state of matter

particle diagram - close together random
movement of particles - move around each other
relative energy of particles - middle stored energy


gas state of matter

particle diagram - far apart random
movement of particles - fast in all directions
relative energy of particles - most stored energy


what is it called when state changes from solid to gas



what is it called when state changes from gas to solid



At its melting point a substance begins to

- melt if energy is transferred to the particles
- freeze if energy is transferred to the surroundings


At its boiling point a substance begins to

- boil if energy is transferred to the particles
- condense if energy is transferred to the surroundings


define element

a substance that contains only of with atoms with the same atomic number (the same number of protons in atoms made of only one element
-e.g. oxygen


define compound

a substance that contains of atoms of two or more different elements chemically joined together
-e.g. water, consists of hydrogen atoms and oxygen atoms chemically joined


a pure substance

contains only one element or substance
- e.g. hydrogen contains only hydrogen atoms, water contains only water atoms


a mixture

contains more than one element and/or compound, mixtures are impure.
mixtures are not chemically bonded.


Elements exist as

atoms or molecules


Hydrogen and Oxygen exist as

simple molecules


carbon exists as

giant molecules (diamond, graphite and graphene)


compounds exist as

- molecules e.g. water H2O
- ionic structures


Air is a mixture of

- elements such as nitrogen, oxygen and argon
- compounds such as water and carbon dioxide


if a substance is pure it will

have a sharp melting point dues to the horizontal line


if a substance is a mixture it would

melt over a range of temperatures


you can separate liquids from mixtures using



you use simple distillation to

separate a solvent from a solution, e.g. water from sea water


the condenser has two

tubes, one inside the other, cold water runs through the space in between keeping it cold


simple distillation works because

the solute in the solution has a higher boiling point than the solvent
when the solution is heated;
- the solvent boils
- solvent vapour passes into the condenser
- the vapour is cooled and condensed back to the liquid state
the solution becomes more concentrated


you use fractional distillation to separate

a liquid from a mixture of miscible liquids (liquids that mix completely with eachother)
e.g. ethanol from water


the fractionating column has a temperature gradient:

hottest and the bottom, coldest at the top


Fractional distillation works because

the liquids in the mixture have different boiling points
when the mixture is heated:
- the mixture boils
- hot vapour rises up the fractionating column
- vapour condenses when it hits the cool surface of the column and drips back
- the fraction with the lowest boiling point reaches the top of the column first
- its vapour passes into the condenser
if you carry on heating, vapours from fractions with higher boiling points pass into the condenser


You can use filtration to

separate an insoluble substance from a liquid or solution.


name two reasons for using filtration

- to purify a liquid by removing solid impurities e.g. sand from sea water
- to separate the solid you want from the liquid its mixed with e.g. to separate crystals from a solution after crystallisation


Filtration works because the filter paper has tiny pores. These are:

- large enough to let water molecules and dissolved substances through
- small enough to stop insoluble solid particles goingt through


You use crystallisation to produce

solid crystals from a solutions


In crystallisation:

- the solution is heated to remove enough solvent to produce a saturated solution (cannot hold more solute)
- the saturated solution is allowed to cool
- CRYSTALS form in the solution
- the crystals are separated from the liquid and dried
a hot water bath gives you more control using a Bunsen burner directly on the evaporating basin


Solubility is the

mass of solute that dissolves in a given volume of solvent at a given temperature


Crystallisation works because

- the solubility of the solute decreases as the saturated solution cools
- crystals form from the excess solute


Paper chromatography is used to

separate mixtures of soluble substances


In chromatography there are two phases:

1. a stationary phase (s substance that doesn't move)
2. a mobile phase (a substance that moves through the stationary phases - the solvent)


During chromatography

- each soluble substance in the mixture forms bonds with the two phases
- substances that from stronger attractive forces with the stationary phase stay near the bottom
- substances that form stronger attractive forces with the mobile phase move towards the top


Using a chromatograph to

- distinguish between pure and impure substances (a pure substance will produce only one spot)
- identify a substance by comparing its pattern of spots with those of a known substance
- identify substances using Rf values


Rf values

Rf = distance travelled by spot ÷ distance travelled by solvent (measure in millimetres)
- Rf values have no unit, they range from 0 (spot stays on baseline) to 1 (spot travels with solvent front)


to investigate the composition of inks you can use

simple distillation and paper chromatography


Waste water and ground water must be treated

to make the water potable or safe to drink


Potable drinking water must have

- low levels of contaminating substances
- low levels of microbes


Fresh water from reservoirs, lakes and rivers is likely to contain

- objects like leaves and twigs
- insoluble solids such as particles of soil
- microbes, which can cause disease
water must be treated to remove these


Sea water can be made potable by simple distillation

- filtered sea water is boiled
- the water vapour is cooled and condensed to form distilled water


Stages in water treatment

1. sedimentation - large insoluble particles sink to the bottom of the tank
2. filtration - small insoluble particles are removed by filtering through beds of sand
3. chlorination - chlorine gas in bubbled from water to kill microbes


simple distillation of sea water:

- uses a plentiful raw material
- produces pure water
- kills microbes in sea water
- needs a lot of energy to heat the water