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

Question 1

solid state of matter

Answer 1

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

Question 2

liquid state of matter

Answer 2

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

Question 3

gas state of matter

Answer 3

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

Question 4

what is it called when state changes from solid to gas

Answer 4

sublimation

Question 5

what is it called when state changes from gas to solid

Answer 5

desublimation

Question 6

At its melting point a substance begins to

Answer 6

• melt if energy is transferred to the particles

- freeze if energy is transferred to the surroundings

Question 7

At its boiling point a substance begins to

Answer 7

• boil if energy is transferred to the particles

- condense if energy is transferred to the surroundings

Question 8

define element

Answer 8

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

Question 9

define compound

Answer 9

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

Question 10

a pure substance

Answer 10

contains only one element or substance

- e.g. hydrogen contains only hydrogen atoms, water contains only water atoms

Question 11

a mixture

Answer 11

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

Question 12

Elements exist as

Answer 12

atoms or molecules

Question 13

Hydrogen and Oxygen exist as

Answer 13

simple molecules

Question 14

carbon exists as

Answer 14

giant molecules (diamond, graphite and graphene)

Question 15

compounds exist as

Answer 15

• molecules e.g. water H2O

- ionic structures

Question 16

Air is a mixture of

Answer 16

• elements such as nitrogen, oxygen and argon

- compounds such as water and carbon dioxide

Question 17

if a substance is pure it will

Answer 17

have a sharp melting point dues to the horizontal line

Question 18

if a substance is a mixture it would

Answer 18

melt over a range of temperatures

Question 19

you can separate liquids from mixtures using

Answer 19

distilation

Question 20

you use simple distillation to

Answer 20

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

Question 21

the condenser has two

Answer 21

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

Question 22

simple distillation works because

Answer 22

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

Question 23

you use fractional distillation to separate

Answer 23

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

Question 24

the fractionating column has a temperature gradient:

Answer 24

hottest and the bottom, coldest at the top

Question 25

Fractional distillation works because

Answer 25

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

Question 26

You can use filtration to

Answer 26

separate an insoluble substance from a liquid or solution.

Question 27

name two reasons for using filtration

Answer 27

• 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

Question 28

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

Answer 28

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

Question 29

You use crystallisation to produce

Answer 29

solid crystals from a solutions

Question 30

In crystallisation:

Answer 30

• 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

Question 31

Solubility is the

Answer 31

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

Question 32

Crystallisation works because

Answer 32

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

Question 33

Paper chromatography is used to

Answer 33

separate mixtures of soluble substances

Question 34

In chromatography there are two phases:

Answer 34

1. a stationary phase (s substance that doesn’t move)

2. a mobile phase (a substance that moves through the stationary phases - the solvent)

Question 35

During chromatography

Answer 35

• 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

Question 36

Using a chromatograph to

Answer 36

• 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

Question 37

Rf values

Answer 37

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)

Question 38

to investigate the composition of inks you can use

Answer 38

simple distillation and paper chromatography

Question 39

Waste water and ground water must be treated

Answer 39

to make the water potable or safe to drink

Question 40

Potable drinking water must have

Answer 40

• low levels of contaminating substances

- low levels of microbes

Question 41

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

Answer 41

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

Question 42

Sea water can be made potable by simple distillation

Answer 42

• filtered sea water is boiled

- the water vapour is cooled and condensed to form distilled water

Question 43

Stages in water treatment

Answer 43

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

Question 44

simple distillation of sea water:

Answer 44

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