CC1/2- States Of Matter/ Methods Of Purifying Substances

Question 1

What are the three states of matter?

Answer 1

• solid
• liquid
• gas

Question 2

Describe the particle model of solids and the energy and forces within them.

Answer 2

• the particles are very close and in a regular lattice
• there are strong forces of attraction between particles, which hold them in fixed positions in a regular lattice arrangement
• the particles don’t move from their positions, so they all keep a definite shape and volume.
• the particles do not have much energy
• they do not move like liquids and gases do and rather vibrate in their fixed positions, the more the temperature increases, the more they vibrate (this is why solids expand when heated)

Question 3

Describe the particle model of liquids and the energy and forces within them.

Answer 3

• the particles are close together but random, they are able to move freely past each other, not maintaining a definite shape
• there is some force of attraction between the particles
• they are free to move past eachother, but they usually stick together
• they do not keep a definite shape so will flow to fill a container, when doing this they always maintain the same volume
• particles in the liquid will have more energy than particles in a solid state but less energy than those in a gas state.
• particles are constantly moving with random motion
• the hotter the liquid gets, the faster they move and it also causes them to expand slightly when heated

Question 4

Describe the particle model of gases and the energy and forces within them.

Answer 4

• the particles in gases are random and far apart
• there are no forces of attraction between the particles, therefore they are free to move
• they travel in straight lines and often collide
• gases don’t keep a definite shape or volume so therefore will always fill a container, when particles bounce off the walls of a container they exert pressure on the walls.
• for any substance particles in the gas state will have will have more energy than in the solid state or the liquid state
• the particles move constantly with random motion
• the hotter the gas gets, the faster the particles move therefore gases will either expand when heated or their pressure will increase

Question 5

What are state changes?

Answer 5

• state changes are physical changes that can be reversed since the chemical properties of the substance do not change
• this is because the particles themselves do not change, only their arrangement, movement and amount of stored energy

Question 6

Describe the process of a solid turning into a liquid.

Answer 6

MELTING
- when a solid is heated, it’s particles gain more energy causing them to vibrate more which weakens the forces that hold the solid together, this causes the solid to expand
- at a certain temperature (varying by substance) the particles will have enough energy to break free from their positions.
- this causes them to melt and the solids turn into liquids

Question 7

Describe the process of liquids turning into gases.

Answer 7

EVAPORATION
- when a liquid is heated, the particles gain energy making them move a lot faster which weakens and breaks the bonds holding the liquid together
- at a certain temperature (varying based on substance) the particles will have enough energy to break their bonds
- this is evaporation and it will turn the liquid into a gas.

Question 8

Describe the process of a gas turning into a liquid.

Answer 8

CONDENSATION
- as a gas is cooled, it’s particles will eventually stop moving extremely fast and transfer energy to the surroundings, eventually forming a liquid
- this is condensation and it causes a gas to become liquid

Question 9

Describe the process of a liquid turning into a solid.

Answer 9

FREEZING
- as the liquid is cooled energy is transferred to the surroundings and the particles start to become fixed, creating a solid.

Question 10

Describe the process of solids turning into gases.

Answer 10

SUBLIMATION

Question 11

Describe a heating curve for water.

Answer 11

• as you add heat to a solid (increase the energy of the particles) the temperature will rise. This energy is weakening and breaking the forces of attraction between the particles allow a change in state
• at some point it will stop rising and the line will become constant- this means it is changing state and melting to become a liquid
• eventually all the solid will melt into a liquids and the temperature will start to rise again
• the same thing will happen and the graph will become horizontal when the liquid starts to change state by boiling and becoming a gas
• it will continue to rise where the gas will evaporate

Question 12

What are some flaws of the particle model?

Answer 12

• particles are not actually solid, i elastic spheres
• doesn’t include any details on the forces between particles, nothing about how strong they are or how many there are

Question 13

Describe exactly what happens between particles when freezing.

Answer 13

• energy is transferred form the particles to the surrounding since many attractive forces must be formed

Question 14

What is a pure substance?

Answer 14

• a pure substance is a substance that is completely made up of a single element or compound
• the composition of a pure substance cannot be changed and is the same in all parts

Question 15

What is a mixture?

Answer 15

• contains elements and/or compounds that are not chemically joined together
• mixtures do not have fixed compositions so they can be separated into different substances using physical processes

Question 16

What is a compound?

Answer 16

• a pure substance that is made of more than one type of element chemically bonded together
• if it was just one element it would be a pure substance
• if it was wasn’t chemically bonded it would be a mixture

Question 17

How can you test for purity using melting points?

Answer 17

• pure substances have the same composition in every part of it so it’s physical properties will be the same all throughout.
• therefore it will have a specific, sharp, high boiling point as all parts of the substance has to change state
• if a substance is a mixture or impure it will melt gradually over a range of temperatures rather than having a sharp melting point

Question 18

What is filtration and how does it work?

Answer 18

• used to separate an insoluble solid from a liquid.
• filter paper is placed in a funnel over a beaker and the mixture is poured into the paper where the soluble liquid will pass through (THE FILTRATE) but larger insoluble pieces will be left behind as RESIDUE

Question 19

What is crystallisation and how does it work?

Answer 19

• separates a soluble solid from a solution
• a filtered solution (the filtrate) will be poured into an evaporating dish and the solution will be gently heated over a Bunsen burner
• it will sit on a tripod as well as a gauze. Sometimes a beaker of water can be placed in between the dish and tripod so that the solution can be heating with the steam that is evaporating from the beaker
• some of the water will evaporate meaning that the solution will be more concentrated
• when the crystals start to form the solution is left to cool
• the salt will form crystals and it is insoluble in the highly concentrated solution
• the crystals can be filtered out the solution and left in a dry oven

Question 20

What are some hazards that can occur when crystallisation is being done?

Answer 20

• the solution may spit hot liquid
• this hazard can be reduced by wearing eye protection, removing the Bunsen burner before the solution is completely dry or rather than placing the Bunsen burner flame directly onto the evaporating basin, it can first heat up a flask of water which can then heat up the solution with fumes.

Question 21

What is chromatography?

Answer 21

• a method used to separate a mixture of soluble substances and identify them
• it has a mobile phase: where the molecules can move (a liquid or gas) and a stationary phase: where the molecules cannot move (a solid or thick liquid)
• components in the mixture will separate out as the mobile phase will move faster that the stationary phase so will end up in a different place
• this allows the components to become separated as each of the chemicals in a mixture will spend different amounts of time either dissolved in the mobile phase or stationary

Question 22

Describe paper chromotography.

Answer 22

• when a solvent moves up along a strip of paper it carries different substances in the mixture at different speeds causing them to be separated.
• the solvent is the mobile phase and the paper is the stationary phase that the solvents and dissolved substances will move through
• the paper with separated components is called a chromatogram

Question 23

Describe the steps of paper chromatography with inks.

Answer 23

1. On a piece of chromatography paper draw a pencil line neat the bottom of the paper, this is the baseline
2. Add spots of ink to the pencil line
3. Add your solvent into the beaker but not to the point it submerged the pencil line and inks
4. The solvent will then start to move up the paper and the chemicals in the mixture will start to dissolve and move up with it
5. Different chemicals in the mixture will be in separate places
6. Remove the paper from the beaker and mark the distance the solvent moved, also mark the distances travelled by each ink in order to calculate the rf value.

Question 24

Why do you use a pencil line in chromatography?

Answer 24

• pencil marks are insoluble so they won’t move with the solvent like ink will

Question 25

What are some conclusions that come from paper chromatography?

Answer 25

• molecules with higher solubility in the solvent and less attraction to the paper will spend more time in the mobile phase therefore they will be carried further up the paper
• components that are insoluble in the mobile phase will not move and will remain as a dot on the pencil line.

Question 26

How do you calculate the rf value?

Answer 26

• rf= distance travelled by solute/distance travelled by solvent

Question 27

How can you use chromatography to test for purity?

Answer 27

• a pure substance will not be separated by chromatography, it will just move as one dot
• a mixture would separate into multiple spots

Question 28

What is distillation?

Answer 28

• used to separate out a liquid out from a solution.
• for example pure drinking water can be obtained from a solution like sea water or tap water

Question 29

Explain the steps of simply distillating pure water from sea water?

Answer 29

1. Pour a sample of seawater into a distillation flask
2. Connect this to a condenser, which will send water into a beaker. The condenser will have a jacket around its tube which at the bottom end will be connected to a cold tap, using rubber tubing. This allows the condenser to keep cool by having cold water circulate around it.
3. Then heat the distillation flask, so that the part of the solution that has the lowest boiling point (the water) evaporates and rises up the flask.
4. The water vapour will pass into the condenser where it will cool and condense (turn back into a liquid), and then flow into the beaker where it is collected as pure, distilled water.
5. Eventually, when this all becomes condensed, there will just be salt left in the flask.

Question 30

What are some issues with simple distillation?

Answer 30

• you can only use it to separate mixtures with a very different boiling points, if they have similar boiling points, they will not be separated
• Therefore you’ll need another method (fraction distillation) 

Question 31

What is fraction distillation?

Answer 31

• Fractional distillation is used to separate a mixture of liquids into fractions
• The first fraction will contain the liquids in the mixture with the lowest boiling point
• these fractions could be single, pure liquid, or they could still be mixtures

Question 32

Describe the steps of fractional distillation.

Answer 32

• put your mixture in a flask and attach it to a fractionating column. The fractionating column will also be attached to a condenser.
• The condenser will have the same jacket of cold water circulating around its tube, allowing the liquid to condense (turn into liquid)
  1. gradually heat up the flask since all the different liquids will have different boiling points they will evaporate at different temperatures.
  2. The liquid with the lowest boiling point or evaporate first and rise to the top of the column. However, sometimes liquids with higher boiling point can also evaporate and rise, but the column is cooler towards the top. these liquids with high boiling points will only get halfway up until it cools down and condenses and is forced to go back into the flask.
  3. Once the first liquid has been collected in a test tube, raise the temperature and collect the next liquid in a different test tube.

Question 33

What is potable water?

Answer 33

• water that is safe to drink.

Question 34

Where do we get water from in the UK?

Answer 34

• Surface water- from lakes, rivers, and reservoirs however, the start to run dry during hotter seasons
• groundwater- these come from aquifers (these are rocks at trap water underground), usually quite pure
• Waste water- water that has been contaminated by human processes, treating this waste water to make a portable is preferable, disposing it which can be polluting

Question 35

What are four methods of water purification?

Answer 35

• filtration
• sedimentation
• chlorination
• desalination

Question 36

How does filtration work to purify water?

Answer 36

• A wire mesh can scream out large bits of sediment like twigs
• Then gravel and sand beds can filter out any other smaller solid bits

Question 37

How does sedimentation work to purify water?

Answer 37

• Iron sulphate or aluminium sulphate can be added to water which makes fine particles clump together and settle at the bottom, this way impure substances can be separated

Question 38

How does chlorination purify water?

Answer 38

• Chlorine can be added to kill harmful bacteria and micro organisms

Question 39

How does desalination work to produce drinking water?

Answer 39

• desalination is done to seawater, which has far too high of a concentration of dissolved salts for us to drink safely
• this can be achieved with simple distillation
• seawater will be heated so that water vapour leaves it quickly. This vapour is then cooled and condensed forming water without dissolved salts.

Question 40

What are some drawbacks to using simple distillation to produce drinking water?

Answer 40

• A lot of energy must be transferred to seawater during such a simple distillation, so it’s not suitable for producing large volumes of drinking water
• it is expensive due to how much energy is needed

Question 41

Why must what are used in chemical analysis be pure?

Answer 41

• The water used for chemical analysis should not contain any dissolved salts. Otherwise incorrect results will be obtained.
• For example, tapwater can contain small amounts of dissolved salt, which can react to form unexpected, cloudy precipitate