Topic 3: States Of Matter And Purifying

Question 1

What is the particle model?

Answer 1

It explains state changes in a substance in terms of the arrangement, movement and energy stored in its particles.

Question 2

Describe the arrangement and movement of gas particles?

Answer 2

Randomly arranged and far apart. They have a lot of kinetic energy so move fast in all directions.

Question 3

Describe the arrangement and movement of liquid particles?

Answer 3

Arranged randomly with about 50% of particles touching. The rollover each other and move around each other.

Question 4

Describe the arrangement and movement of solid particles?

Answer 4

Regular, close together and vibrate about a fixed position.

Question 5

What type of change is a state change?

Answer 5

Physical change. They can be reversed and the chemical properties of the substance do not change.

Question 6

Why did the chemical properties of a substance going through a state change not change?

Answer 6

Because the particles themselves do not change, only their arrangement, movement and amount of stored energy.

Question 7

What are the forces attraction between particles?

Answer 7

Particles are attracted to each other by weak forces of attraction. There are many of these forces in a solid. Some of these are over come during melting. The remaining attractive forces between particles in a liquid are overcome during evaporation and boiling.

Question 8

What type of reaction happens during evaporation/boiling.

Answer 8

Exothermic - energy must be transferred from the surroundings to the particles.

Question 9

During condensation what time of reaction takes place?

Answer 9

Endothermic - energy is transferred from particles to surroundings.this is why water vapour turns into water droplets.

Question 10

How can you predict the state of a substance?

Answer 10

• below it’s melting point, the substance in solid.
• between the melting and boiling point, substance is liquid.
• above the boiling point the substance is a gas.

Question 11

What is the composition of a pure substance?

Answer 11

• cannot be changed

- is the same in all parts of a piece of the substance.

Question 12

Can compounds be pure and why?

Answer 12

Yes along as it is the same in all parts of the substance.

Question 13

What is a mixture?

Answer 13

This contains elements/compounds that are not chemically joined together. You can use physical processes to separate mixtures into different substances. It does not have a fixed composition.

Question 14

Can you use physical methods to separate out pure substances?

Answer 14

No because it has the same fixed position in all its parts.

Question 15

How does a solid turn into a liquid?

Answer 15

It’s particles gain enough energy to overcome the weak forces of attraction between them. They move further away from one another and the solid becomes a liquid. This is the melting point.

Question 16

Define physical property:

Answer 16

How a substance responds to forces of energy.

Question 17

Why does a pure substance melt at one temperature?

Answer 17

It has the same composition in every part so the same physical properties in every part. So all the pure substance will melt at the same temperature until it has changed state.

Question 18

What does a filter do?

Answer 18

They can be used separate some mixtures. They let smaller pieces or liquids through but trap bigger pieces or insoluble substances.

Question 19

Give some examples where filtration is used?

Answer 19

Cars, vacuum cleaners and air conditioning.

Question 20

What is a solution and a solvent?

Answer 20

A solution is a mixture made of solutes in a liquid called a solvent.

Question 21

How can solutes be separated from a solution/what is crystallisation?

Answer 21

By evaporating the solvent to leave the solute behind. This solute forms crystals.

Question 22

How are the crystals from crystallisation formed?

Answer 22

If the crystals form slowly, the particles have longer to form an ordered pattern and will make larger crystals.

Question 23

What is a saturated solution?

Answer 23

Contains the maximum amount of a solute that can dissolve in that amount of solvent at that temperature.

Question 24

What is the process of forming table salt?

Answer 24

• Produced from sea water/dug out of ground/solution mining.
• water is pumped into layers of salt underground.
• the resulting salt solution is then heated, which evaporated the solvent and makes the solution more salty.
• eventually it reaches the state if a saturated solution.
• it is then evaporated to form crystals

Question 25

Give the steps for filtration and crystallisation in a lab:

Answer 25

• filter funnel is lined with filter paper that has dune holes init.
• the solvent and solute(s) pass through this to form the filtrate.
• bits of insoluble substances cannot fit through the holes and so leave a residue in the filter paper.
• Bunsen burner is then used to evaporate the filtrate carefully. Care must be taken not to over heat solution once saturated because crystals may spit out or chemically change.

Question 26

What is identifies in a risk assessment?

Answer 26

In a risk assessment, the hazards of doing an experiment are identified. A hazard is something that could cause harm. Then a safety precaution is considered.

Question 27

Give a risk assessment for filtration/crystallisation:

Answer 27

During crystallisation the risks from spitting can be rejected by wearing eye protection, removing the Bunsen burner before the solution is completely dry and/or using steam to heat evaporating Bain gently.

Question 28

How is chromatography used?

Answer 28

It is used to find out which colour compounds a mixture contains.

Question 29

How does paper chromatography work?

Answer 29

It is a simpler technique because some compounds dissolve better in a solvent than other. When the solvent moves along the strip of paper it carries the different substances in the mixture at different speeds, so they are separated.

Question 30

What is the mobile phase?

Answer 30

The solvent.

Question 31

What is the stationary phase?

Answer 31

The chromatography paper.

Question 32

What is a chromatogram?

Answer 32

The chromatography paper with the separated components.

Question 33

What is the Rf value and how can it be calculated?

Answer 33

It is the distance the compound has risen divided by the distance the solvent has written.

Rf = distance moved by spot/ distance moved by solvent

Question 34

What must the Rf value always be under and why?

Answer 34

A compound never rises as fast as the solvent so Rf values are always less than 1.

Question 35

Give 3 uses of paper chromatography:

Answer 35

• distinguish between pure and impure substances.
• identify substances that by comparing the pattern on the chromatogram with the patterns formed by known substances.
• identify substances by calculating their Rf value.

Question 36

Why must the solvent not be past the line on the chromatography paper?

Answer 36

Cause errors to prevent the spots getting dissolved into the mobile phase.

Question 37

Why is it better to use pure water for a chemical analysis and how do you do that?

Answer 37

Because water from the tap contains dissolved ions that may interfere with results. Water can be purified through distillation.

Question 38

The steps of simple distillation:

Answer 38

• When mineral water evaporates, only the water turns to gas.
• the solid minerals, which have a higher boiling point, are left behind.
• the water vapour is now pure and is condensed back into liquid water.
• the process of evaporation followed by condensation is called distillation. The apparatus is called a still.

Question 39

Why might simple distillation using a delivery tube nit be the best way?

Answer 39

Not very efficient because much if the vapour is lost.

Question 40

What do anti bumping granules do?

Answer 40

Make liquid boil more smoothly - small bubbles of vapour form on the corners of the granules and reduce risk of liquid boiling over.

Question 41

What is a condenser?

Answer 41

A central tube surrounded by a jacket of cold water. It helps transport the water vapour and condense it to water.

Question 42

How does fractional distillation work?

Answer 42

It can be used to speedster two or more liquids. This works because some liquids boil more easily than others. Liquids with lower boiling points evaporate more easily than others and will turn into vapour first. The first fraction collected has the lowest boiling point. The fractions may be lure liquids or still mixtures.

Question 43

Give 3 examples that use fractional distillation:

Answer 43

• to separate the different products of crude oil.
• to make alcoholic drinks such as whisky and vodka.
• to separate out the gases in the air, after air has been called and turned into liquid at -200 degrees Celsius.

Question 44

Give the steps of fractional distillation:

Answer 44

• A column is fixed above the distillation flask. The hot vapour rises up the column.
• at first the vapour condenses when it hits the cool glass and rips back down into the flask.
• as the column gradually heats up there will be a temperature gradient. Hottest at the bottom and temperature will drop as you go further up the column.
• the fraction with the lowest boiling point will reach the top of the column first and vapour will then pass into condenser.
• if you keep heating, fractions with higher boiling points will then rise up the column and be collected later.

Question 45

What is desalination?

Answer 45

Producing pure water from sea water and can be achieved using simple distillation.

Question 46

What are the steps for desalination?

Answer 46

• water is separated from dissolved salts using simple distillation.
• sea water is then heated so that water vapour leaves quickly. Vapour is then cooled and condensed, forming water without the dissolved salts.

Question 47

Why is simple distillation not a suitable method for desalination?

Answer 47

A lot of energy must be transferred to sea water during simple distillation, so it is not usually a suitable method for producing large volumes of drinking water.

Question 48

What does chemical analysis involve and why must distilled water be used?

Answer 48

Using chemical reactions or sensitive machines to identify and measure the substances in a sample. The water used for chemical analysis should not contain any dissolved salts, which may react to form an unexpected cloudy precipitates. These may hide the correct results of the analysis leading to unreliable results.

Question 49

Where does the raw material for producing drinking water come from?

Answer 49

Rivers, lakes or aquifers. The water from these sources are often stored in reservoirs.

Question 50

Fresh water firm reservoirs contain?

Answer 50

• Objects such as twigs or leaves
• small insoluble particles such as grit and slit
• soluble substances, including salts, pesticides and fertilisers.
• bacteria and other microbes that maybe harmful tot health.

Question 51

What are the different steps used to deal with impurities in drinking water?

Answer 51

Screening-using a sieve to get rid of large objects (twigs, stones etc)
sedimentation-small particles are allowed to settle outa d filtration using tanks containing beds of sand and gravel.
Chlorination-chlorine added to water to kill microbes in the now treated water.