topic 2

Question 1

solids

Answer 1

there are strong forces of attraction between particles which hold them in fixed positions in a regular lattice fragment

• don’t move, fixed positions
• don’t have much energy
• vibrate on a spot

Question 2

liquids

Answer 2

• some force of attraction between the particles
• free to move past each other but still touching
• not a definite shape and volume
• more energy
• constantly moving in a random shape
• hotter the liquid gets the faster it moves

Question 3

gases

Answer 3

• no force of attraction
• travel in a straight line and only interact when they collide
• don’t keep a definite shape or volume
• always will a container, exert pressure of the walls
• more energy
• hotter the gas the faster they move

Question 4

liquid to solid

Answer 4

freezing

Question 5

solid to liquid

Answer 5

melting

Question 6

liquid to gas

Answer 6

evaporating

Question 7

gas to liquid

Answer 7

condensing

Question 8

solid to gas

Answer 8

subliming

Question 9

gas to solid

Answer 9

deposition

Question 10

when a solid is heated…

Answer 10

particles gain more energy
they vibrate more
weakens forces making the solid expand
at a certain temperature the particles have enough energy to break free from their positions (melting) and the solid turns into a liquid

Question 11

when a liquid is heated

Answer 11

• the particles get even more energy
• this energy makes the particles move faster which weakens and breaks the bond holding holding the liquid together
• at a certain temp the particles have enough energy to break their bonds. This is called evaporation and the liquid turns into a gas

Question 12

chemical changes for atoms

Answer 12

atoms are rearranged during chemical reaction

• chemical changes are different to physical changes
• chemical changes happen during chemical reactions when bonds between atoms break and the atoms change places.
• the atoms from the substances you start off with (the reactants) are rearranged to form different substances (the products)
• chemical changes are often hard to reverse

Question 13

pure substances

Answer 13

• a substance is pure if it’s completely made up of a single element or
  compound

Question 14

mixtures

Answer 14

if you’ve got more than one compound present or different elements that aren;t all part of a single compunds

Question 15

testing for purity

Answer 15

you can test for purity using melting points

• every pure substances has a specific, sharp melting and boiling point
• MIXTURES will melt gradually over a range of temperatures
• PURE substances have sharp melting points

Question 16

what is distillation

Answer 16

used to separate mixtures that contain liquids. Two types: simple and fractional

Question 17

what is simple distillation

Answer 17

used for separating out a liquid from a solution
For example, water can be separated from salt solution by simple distillation. This method works because water has a much lower boiling point than salt. When the solution is heated, the water evaporates. It is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.

Question 18

what is fractional distillation

Answer 18

Fractional distillation is a method for separating a liquid from a mixture of two or more liquids. For example, liquid ethanol can be separated from a mixture of ethanol and water by fractional distillation. This method works because the liquids in the mixture have different boiling points. When the mixture is heated, one liquid evaporates before the other.

Question 19

what is filtration

Answer 19

if the product of a reaction is an insoluble solid, you can use filtration to separate it out from the liquid reaction mixture
- put some filter paper into a funnel and pour in your mixture. The liquid part of the mixture runs through the paper leaving behind a solid residue

Question 20

crystallisation

Answer 20

separates a soluble solid from a solution
To obtain large, regularly shaped crystals:

put the solution in an evaporating basin
warm the solution by placing the evaporating basin over a boiling water bath
stop heating before all the solvent has evaporated
After the remaining solution has cooled down, pour the excess liquid away (or filter it). Dry the crystals using a warm oven or in air.

Question 21

chromatography

Answer 21

a method used to separate a mixture of soluble substances and identify them

there are two phrases: mobile phase and
stationary phase

Question 22

chromatography mobile phase

Answer 22

where the molecules CAN move. This is always a liquid or a gas

Question 23

chromatography stationary phase

Answer 23

where the molecules CAN’T move. This can be a solid or a really thick liquid

Question 24

mixtures in mobile and stationary phase

Answer 24

the components in the mixture separate out as the mobile phase moves over the stationary phase - they all end up in different places in the stationary phase
- this happens because the chemicals spend different amounts of time dissolved in the mobile phase and stick to the stationary phase.

Question 25

paper chromatography

Answer 25

in paper chromatography the stationary phase is a piece of filter paper and the mobile phase is a solvent (e.g water or ethanol) a pure substance produces one spot on the chromatogram an impure substance produces two or more spots

Question 26

stages in paper chromatography

Answer 26

the stationary phase, which in paper chromatography is very uniform, absorbent paper the mobile phase is the solvent that moves through the paper, carrying different substances with it molecules with higher solubility (less attracted to the paper) will spend more time in the mobile phase

Question 27

method for paper chromatography

Answer 27

1. line at the bottom of the paper 2. draw spots of the line 3. dip paper in breaker with solvent 3. the solvent will start to move up the paper 4. see spots forming at different points on the paper

Question 28

calcualting Rf

Answer 28

distance travelled by solute/ distance travelled by solvent ratio between the distance travelled by the dissolved substances (solute) and the distance travelled by the solvent

Question 29

3 water purifying treatments

Answer 29

filtration sedimentation chlorination

Question 30

filtration (water)

Answer 30

a wire mesh screens out large twigs and then gravel and sand beds filter out any other solid bits

Question 31

sedimentation (water)

Answer 31

iron sulfate or aluminium sulfate is added to the water, which makes fine particles clump together and settle at the bottom

Question 32

chlorination (water)

Answer 32

chlorine gas is bubbled through to kill harmful bacteria and other microbes

Question 33

why can normal water give a false result

Answer 33

it has small amounts of ions (such as calcium, iron and copper) that can interfere with reactions deionised water is used instead - ions have been removed

Question 34

purifying sea water

Answer 34

simple distillation - sea water is heated so that water vapour leaves it quickly - the water is then cooled and condensed forming water without the dissolved salts

Question 35

water for drinking

Answer 35

water from water source - sedimentation tank (small particles settle out) - filtration 9using tanks containing beds of sand and gravel) - choline is added in a process called chlorination (kills microorganisms in the treated water)