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Chemistry GCSE > topic 2 - states of matter and mixtures > Flashcards

topic 2 - states of matter and mixtures Flashcards

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1
Q

features of solids (7)

A
  • 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
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2
Q

features of liquids (7)

A
  • 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
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3
Q

features of gases (7)

A
  • 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
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4
Q

melting (4)

A

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

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5
Q

boiling/evaporating (4)

A

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

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6
Q

condensing (4)

A

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

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7
Q

freezing (4)

A

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

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8
Q

sublimation

A

solid -> gas

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9
Q

desublimation

A

gas -> solid

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10
Q

pure substance

A

a substance completely made up of a single element or compound

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11
Q

mixture

A

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

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12
Q

how to test for purity (2)

A

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

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13
Q

what can you use to test melting point (2)

A
  • melting point apparatus

- a water bath and a thermometer

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14
Q

what is simple distillation used for

A

separating a liquid from a solution

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15
Q

how to distil a substance using simple distillation (6)

A

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)

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16
Q

what is a problem with simple distillation

A

it is hard to separate liquids with similar boiling points

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17
Q

what is fractional distillation used for

A

separating a mixture of liquids

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18
Q

how to do fractional distillation (5)

A

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

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19
Q

what is filtration used for

A

separating an insoluble solid from a liquid

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20
Q

how to do filtration

A

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

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21
Q

what is crystallisation used for

A

separating a soluble solid from solution

22
Q

how to do crystallisation (4)

A

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

23
Q

what is a desiccator

A

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

24
Q

what is chromatography used for

A

separating a mixture of soluble substances and identifying them

25
Q

what are the two phases of chromatography

A

mobile phase

stationary phase

26
Q

mobile phase

A

where th molecules can move

gas or liquid

27
Q

stationary phase

A

where the molecules can’t move

can be a solid or very thick liquid

28
Q

when do components separate out

A

when the mobile phase moves over the stationary phase

29
Q

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

A

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

30
Q

what is the process of chromatography (6)

A

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

31
Q

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

A

repeat in another solvent

32
Q

what if some chemical are colourless (chromatography)

A

you may need to spray the chromatogram with locating agent

33
Q

Rf value definition

A

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

34
Q

Rf value formula

A

Rf = distance travelled by solute / distance travelled by solvent

35
Q

what does Rf depend on

A

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)

36
Q

how can you use chromatography to test purity

A

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

37
Q

what are SRMS and what are they used for

A

standard reference materials are pure materials

they are run next to a mixture to check a component’s identity

38
Q

ink

A

a mixture of different dyes dissolved in solvent

39
Q

how to work out the solvent of an ink

A

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

40
Q

how to separate the dyes in an ink

A

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

41
Q

3 sources of water

A

surface water
ground water
waste water

42
Q

surface water

A

from lakes, rivers and reservoirs

in England and Wales, in the summer these start to run dry

43
Q

ground water

A

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

44
Q

waste water

A

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

45
Q

3 stages of water treatment/purification

A

filtration
sedimentation
chlorination

46
Q

filtration

A

a wire mesh screens out large twigs

then gravel and sand beds filter out other solid bits

47
Q

sedimentation

A

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

48
Q

chlorination

A

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

49
Q

how else can drinking water be obtained

A

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)

50
Q

importance of pure water

A

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

Chemistry GCSE (15 decks)

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