topic 2 - states of matter and mixtures

Question 1

features of solids (7)

Answer 1

• strong forces of attraction
• don’t move from fixed lattice
• not much energy
• definite shape
• definite volume
• can only vibrate in fixed positions
• expands slightly when heated

Question 2

features of liquids (7)

Answer 2

• some forces of attraction
• particles move past each other but tend to stick together
• more energy than solid
• no definite shape
• definite volume
• move with random motion
• expand slightly when heated

Question 3

features of gases (7)

Answer 3

• nearly no forces of attraction
• free to move
• more energy than liquid
• no definite shape
• no definite volume
• move with random motion
• when heated, expand or pressure increases

Question 4

melting (4)

Answer 4

solid -> liquid
particles gain energy as substance if heated
they vibrate more, weakening forces holding solid together
at melting point, particles have enough energy to break free and become a liquid

Question 5

boiling/evaporating (4)

Answer 5

liquid -> gas
particles gain even more energy
particles move faster, weakening and breaking bonds holding liquid together
at the boiling point, particles break bonds to become a gas

Question 6

condensing (4)

Answer 6

gas -> liquid
gas cools and particles no longer have enough energy to overcome forces of attraction
bonds form
at the boiling point, bonds have formed to become a liquid

Question 7

freezing (4)

Answer 7

liquid -> solid
particles have less energy and particles don’t have enough energy to overcome forces of attraction
bonds form
at the melting point, so many bonds have formed that it is a solig

Question 8

sublimation

Answer 8

solid -> gas

Question 9

desublimation

Answer 9

gas -> solid

Question 10

pure substance

Answer 10

a substance completely made up of a single element or compound

Question 11

mixture

Answer 11

a substance containing more than one compound or there are different elements not part of a single compound

Question 12

how to test for purity (2)

Answer 12

every substance has specific melting and boiling point
you can test for purity by comparing the melting point of the sample to the expected

if a substance is a mixture, it will melt over a range of temperatures instead of at a sharp melting point

Question 13

what can you use to test melting point (2)

Answer 13

• melting point apparatus

- a water bath and a thermometer

Question 14

what is simple distillation used for

Answer 14

separating a liquid from a solution

Question 15

how to distil a substance using simple distillation (6)

Answer 15

1) place substance (eg. seawater) in a distillation flask
2) set up apparatus (Bunsen burner heats flask there is a thermometer condenser and beaker)
3) connect the condenser to a cold tap using rubber tubing
4) gradually heat the flask so that the part of the solution with the lowest boiling point will evaporate
5) this vapour passes into the condenser where it cools and condenses back into a liquid
6) it flows and collects in the beaker (if seawater is used, salt is left in the flask)

Question 16

what is a problem with simple distillation

Answer 16

it is hard to separate liquids with similar boiling points

Question 17

what is fractional distillation used for

Answer 17

separating a mixture of liquids

Question 18

how to do fractional distillation (5)

Answer 18

1) place mixture in flask
2) attach a fractionating column and condenser
3) gradually heat the flask, collect the different liquids as they evaporate at different temperatures
4) there is a temperature gradient in the fractionating column so the column is cooler at the top and so the liquids with the higher boiling points will condense and run back down to the flask
5) once the first liquid has been collected, raise the temperature until the next one reaches the top

Question 19

what is filtration used for

Answer 19

separating an insoluble solid from a liquid

Question 20

how to do filtration

Answer 20

place filter paper into a funnel and pour mixture into it
liquid runs through the paper
solid residue is left behind

Question 21

what is crystallisation used for

Answer 21

separating a soluble solid from solution

Question 22

how to do crystallisation (4)

Answer 22

1) pour solution into an evaporating dish and gently heat so that some water evaporates and the solution becomes more concentrated
2) once it is more concentrated, some crystals should begin to appear
3) remove the dish from the heat and leave the solution to cool
4) filter the crystals out and leave them in a warm place to dry or use a desiccator or a drying oven

Question 23

what is a desiccator

Answer 23

contains a chemical which removes water from the surroundings to dry something out

Question 24

what is chromatography used for

Answer 24

separating a mixture of soluble substances and identifying them

Question 25

what are the two phases of chromatography

Answer 25

mobile phase | stationary phase

Question 26

mobile phase

Answer 26

where th molecules can move | gas or liquid

Question 27

stationary phase

Answer 27

where the molecules can't move | can be a solid or very thick liquid

Question 28

when do components separate out

Answer 28

when the mobile phase moves over the stationary phase

Question 29

why do all components end up in different places in the stationary phase

Answer 29

each of the chemicals in the mixture spend different amounts of time dissolved in the mobile phase and stuck in the stationary phase

Question 30

what is the process of chromatography (6)

Answer 30

1) draw baseline in pencil near the base of the paper 2) put a spot of mixture to be separated on the baseline 3) place some solvent in a beaker 4) dip paper into it 5) put watch glass on top to prevent evaporation of solvent 6) remove the paper and take measurements

Question 31

if one substance is insoluble in one solvent what shoudl you do

Answer 31

repeat in another solvent

Question 32

what if some chemical are colourless (chromatography)

Answer 32

you may need to spray the chromatogram with locating agent

Question 33

Rf value definition

Answer 33

the ratio between the distance travelled by the solute and the distance travelled by the solvent (always between 0 and 1)

Question 34

Rf value formula

Answer 34

Rf = distance travelled by solute / distance travelled by solvent

Question 35

what does Rf depend on

Answer 35

how soluble the solute is in the solvent how attracted the solute is to the stationary phase (the more soluble, the more time spent in the mobile phase, the further up the paper)

Question 36

how can you use chromatography to test purity

Answer 36

if a substance is pure, you can see if it separates (if it does it is a mixture)

Question 37

what are SRMS and what are they used for

Answer 37

standard reference materials are pure materials | they are run next to a mixture to check a component's identity

Question 38

ink

Answer 38

a mixture of different dyes dissolved in solvent

Question 39

how to work out the solvent of an ink

Answer 39

simple distillation evaporate off the solvent and collect it (assuming it has the lowest boiling point) the thermometer will read the boiling point of the solvent and we can use this to try and identify it

Question 40

how to separate the dyes in an ink

Answer 40

paper chromatography will separate out the different inks so you can see how many there are one can compare the Rf values of the spots with reference values to identify the dyes in the ink

Question 41

3 sources of water

Answer 41

surface water ground water waste water

Question 42

surface water

Answer 42

from lakes, rivers and reservoirs | in England and Wales, in the summer these start to run dry

Question 43

ground water

Answer 43

from aquifers - rocks that trap water underground | in areas of south-east England, where surface water is limited, groundwater provides 70% of the domestic water supply

Question 44

waste water

Answer 44

from water that has been contaminated by a human process | treating waste water to make it potable is preferable to disposing it which can be polluting

Question 45

3 stages of water treatment/purification

Answer 45

filtration sedimentation chlorination

Question 46

filtration

Answer 46

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

Question 47

sedimentation

Answer 47

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

Question 48

chlorination

Answer 48

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

Question 49

how else can drinking water be obtained

Answer 49

distillation of sea water but this requires lots of energy so is really expensive (however this is done in countries such as the middle east where they don't get much rain)

Question 50

importance of pure water

Answer 50

for experiments involving mixing and dissolving something in water, we need deionised water