Topic 2 - States of matter and mixtures

Question 1

Particle Model of Solids

Answer 1

• strong forces of attraction between particles
• close together
• regular arrangement
• vibrate on the spot

Question 2

Particle Model of Liquids

Answer 2

• weak forces of attraction between particles
  -close together
  -irregular arrangement
  -free to move past each other

Question 3

Particle Model of Gases

Answer 3

• very weak forces of attraction between particles
• far apart
• irregular arrangement
• free to move past each other in random motions

Question 4

Solid - Liquid

Answer 4

-melting
- when a solid is heated, its particles gain energy and vibrate more
- weakens the forces that hold the solid together
- at the melting point , the particles have enough energy to break free from their positions

Question 5

Liquid - Gas

Answer 5

-boiling
- when a liquid is heated, its particles gain energy and move faster
- weakens the attractive forces that hold the liquid together
- at the boiling point , the particles have enough energy to overcome any remaining attractive forces

Question 6

Gas - Liquid

Answer 6

• condensing
• as the gas cools, the particles no longer have enough energy to overcome forces of attraction
  -below a certain temp, the forces of attraction become strong enough to convert the gas into a liquid

Question 7

Liquid - Solid

Answer 7

• freezing
  as the liquid cools, the particles no longer have enough energy to overcome forces of attraction
• particles less free to move
  -below melting point , the forces of attraction become strong enough to keep particles held in place in a solid

Question 8

Predicting state of substance

Answer 8

• below melting point : solid
• in between melting &boiling point : liquid
• above boiling point : gas

Question 9

Pure substance

Answer 9

a pure substance is completely made up of only a single element or molecule

Question 10

How to test for pure substances

Answer 10

A chemically pure substance will have a sharp, specific melting and boiling point .
Measure melting point of substance using melting point apparatus and see if it is the same as value in data book

Question 11

Simple Distillation

Answer 11

• separates liquid from a mixture
• water from seawater

Question 12

Simple Distillation Process

Answer 12

• sample poured into distillation flask
• connect bottom of condenser to cold tap to keep it cool
• flask is gradually heated
  -lowest BO component evaporates, vapour passes into the condenser where it condenses,
• collected as a liquid in another container

Question 13

fractional distillation

Answer 13

• separating mixture of different liquids with similar boiling points
  -crude oil

Question 14

fractional distillation - process

Answer 14

• sample poured into distillation flask
• liquid with lowest BO evaporates first, and rises up the fractionating column filled with glass rods
  -it passes into the condenser and is collected back as a liquid
• liquids with higher BO will start to evaporate but only get part way up the column before condensing back down, as it is cooler at the top
• once first liquid is collect, raise the temp to the boiling point of next lowest BO component

Question 15

Filtration

Answer 15

-separate insoluble solid from mixture
- sand from water
- fold filter paper into cone and put it in a filter funnel
-put funnel on neck of a conical flask
-pour mixture through funnel into the flask, the insoluble solid will be collected

Question 16

Crystallisation

Answer 16

-separate soluble solid from mixture
- salt from water
- place evaporating dish on top of a tripod with a gauze mat
- heat the dish using a bunsen burner
- pour solution into evaporating dish and gently heat it
- once crystals start to form, remove it from the heat and it should start to form crystals
- filter crystals out and dry in a desiccator

Question 17

Mobile phase

Answer 17

where the molecules can move. usually a liquid or gas

Question 18

Stationary phase

Answer 18

where the molecules can’t move. in paper chromatography it is paper.

Question 19

What will a pure substance look like

Answer 19

a pure substance will produce a single spot in all solvents

Question 20

Rf value

Answer 20

distance travelled by solute / distance travelled by solvent

Question 21

Why do we use pencil to draw the base line?

Answer 21

if we drew the line in pen, the line would move up the paper with the solvent. pencil is insoluble

Question 22

why does the solvent need to be below the pencil line at the start

Answer 22

if the ink touches the solvent initially it will be washed away

Question 23

Potable water

Answer 23

water that is safe for humans to drink
- contains low levels of salts and microbes

Question 24

sources of water

Answer 24

surface water
ground water
waste water

Question 25

purifying water - filtration

Answer 25

a wire mesh screens out large twigs and sand beds filter out big objects

Question 26

purifying water - sedimentation

Answer 26

iron sulfate is added which makes fine particles clump together

Question 27

purifying water - chlorination

Answer 27

chlorine gas is bubbled through to kill harmful bacteria and microbes

Question 28

desalination

Answer 28

used in dry countries where there isn’t enough surface water or ground water, so saltwater is used instead
distillation or reverse osmosis
it consumes a lot of energy and is very expensive