Topic 2: states of matters and mixture

Question 1

solid to liquid

Answer 1

melting

Question 2

liquid to solid

Answer 2

freezing

Question 3

Liquid to gas

Answer 3

boiling

Question 4

gas to liquid

Answer 4

condensing

Question 5

Melting & freezing

Answer 5

take place at the melting point

Question 6

Boiling & condensing

Answer 6

take place at the boiling point

Question 7

Gas particles

Answer 7

have the most energy as the particles are the most spread out

Question 8

Liquid particles

Answer 8

have more energy than those in a solid,but less than those in a gas

Question 9

Solid particles

Answer 9

have the least energy - particles are fixed

Question 10

What type of changes are state changes? (melting, boiling, freezing and condensing)

Answer 10

State changes (melting, boiling, freezing and condensing) are physical changes –
they involve the forces between the particles of the substances but the particles
themselves don’t change

Question 11

What are chemical changes?

Answer 11

Chemical changes are where a new product has been formed

Question 12

Explain the changes in arrangement, movement and energy of particles
during these interconversions

Answer 12

Particle theory can help to explain melting, boiling, freezing and condensing…
o The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the
particles of the substance.
o The nature of the particles involved depends on the type of bonding and the structure of the substance.
o The stronger the forces between the particles the higher the melting point and boiling point of the substance.

Question 13

If a temperature is below the melting point…

Answer 13

at temperatures below the melting point, the substance will be solid

Question 14

If a temperature is above the melting point but below the boiling point…

Answer 14

at temperatures above the melting point but below the boiling point, the substance will be liquid

Question 15

If a temperature is above the boiling point…

Answer 15

at temperatures above the boiling point, the substance will be a gas

Question 16

What is a mixture?

Answer 16

A mixture:
o Consists of 2 or more elements or compounds not chemically combined
together
o Chemical properties of each substance in the mixture are unchanged

Question 17

Explain the difference between the use of ‘pure’ in chemistry compared with its everyday use

Answer 17

A pure substance = a single element or compound, not mixed with any other substance
HOWEVER
In everyday language, a pure substance = substance that has had nothing added to it, so it is unadulterated and in its natural state, e.g. pure milk

Question 18

How can you determine from melting/boiling point whether a substance is pure or a mixture?

Answer 18

-Pure substances melt and boil at specific/exact temperatures, mixtures do not:
-Mixtures melt over a range of temperatures
due to them consisting of 2 or more elements or compounds

Question 19

Explain the experimental techniques for separation of mixtures by:
simple distillation

Answer 19

Simple distillation:
o Used to separate a pure liquid from a mixture of liquids
▪ Works when the liquids have different boiling points
▪ Commonly used to separate ethanol from water
▪ (Taking the example of ethanol…) ethanol has a lower bp than
water so it evaporates first. The ethanol vapour is then cooled and
condensed inside the condenser to form a pure liquid.
▪ Sequence of events in distillation is as follows: heating ->
evaporating -> cooling -> condensing

Question 20

Explain the experimental techniques for separation of mixtures by:
Fractional distillation

Answer 20

Fractional distillation:
o The oil is heated in the fractionating column and the oil evaporates and
condenses at a number of different temperatures.
o The many hydrocarbons in crude oil can be separated into fractions each
of which contains molecules with a similar number of carbon atoms
o The fractionating column works continuously, heated crude oil is piped in
at the bottom. The vaporised oil rises up the column and the various fractions are constantly tapped off at the different levels where they
condense.
o The fractions can be processed to produce fuels and feedstock for the
petrochemical industry.

Question 21

Explain the experimental techniques for separation of mixtures by:
Filtration

Answer 21

Filtration:
o If you have produced e.g. a precipitate (which is an insoluble salt), you
would want to separate the salt/precipitate from the salt solution.
▪ You would do this by filtering the solution, leaving behind the
precipitate on the filter paper

Question 22

Explain the experimental techniques for separation of mixtures by:
Crystallisation

Answer 22

Crystallisation:
o If you were to have produced a soluble salt and you wanted to separate
this salt from the solution that it was dissolved in
▪ You would first warm the solution in an open container, allowing
the solvent to evaporate, leaving a saturated solution
▪ Allow this solution to cool
▪ The solid will come out of the solution and crystals will start to
grow, these can then be collected and allowed to dry

Question 23

Explain the experimental techniques for separation of mixtures by:
Paper chromatography

Answer 23

▪ Used to separate mixtures and give information to help identify
substances
▪ Involves a stationary phase and a mobile phase
▪ Separation depends on the distribution of substances between
the phases

Question 24

What is the Rf value?

Answer 24

Rf value = distance moved by substance / distance moved by solvent
Different compounds have different Rf values in different solvents, which can be used to help identify the compounds

Question 25

How can you tell if a substance is pure or a mixture in chromatography?

Answer 25

Compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents

Question 26

What is paper chromatography?

Answer 26

paper chromatography is the separation of mixtures of soluble substances by running a solvent (mobile phase) through the mixture on the paper (the paper contains the stationary phase), which causes the substances to move at different rates over the paper

Question 27

Potable water

Answer 27

potable water: it is suitable for drinking so must have:
○ low levels of microbes
○ low levels of contaminating substances
○ it is not the same as pure water but is still safe

Question 28

making waste and ground water potable:

Answer 28

1. sedimentation: large insoluble particles will sink to the bottom of the water
2. filtration: water is filtered through beds of sand which removes small insoluble particles
3. chlorination: chlorine gas is put through water to kill microbes

Question 29

making sea water potable using distillation:

Answer 29

1. filter the seawater
2. boil it
3. water vapour is cooled and condensed

Question 30

water used in analysis:

Answer 30

○ must be pure because any dissolved salts could react with the substances
you are analysing, leaving you with a false result