States of Matter and Mixtures

Question 1

What is Filtration used for?

Answer 1

Used to separate an Insoluble Solid from a liquid

Question 2

What is Crystallisation used for?

Answer 2

Used to separate a soluble solid from a solution

Question 3

Describe the method of filtration

Answer 3

Fold filter paper into a cone shape and put this into a funnel over a beaker. Pour your mixture into the funnel and the liquid runs through the paper into the beaker, leaving behind a solid residue

Question 4

Describe the method of crystallisation

Answer 4

• Pour the solution into an evaporating dish and heat the solution - this concentrates the solution
• Once crystals have formed or some water has evaporated - remove the dish from heat
• The salt will start to form crystals as in become insoluble in he cold, highly concentrated solution
• Filter the crystals out of the solution - leave them in a warm place to dry - drying oven or desiccator

Question 5

What are the 3 states of matter?

Answer 5

Solid, liquid and gas

Question 6

What are the properties of a solid?

Answer 6

• Strong forces of attraction hold particles in fixed positions
• Keep a definite shape and volume
• Don’t have much energy
• Don’t move at all only vibrate in fixed positions, the hotter the more vibration and more expansion

Question 7

What are the properties of a liquid?

Answer 7

• Some force of attraction between particles, free to move past each other but tend to stick together
• Don’t keep definite shape, keep same volume, will fill bottom of container
• More energy than solid state
• The hotter the liquid, the faster moving particles - more energy - causes expansion

Question 8

What are the properties of a gas?

Answer 8

• no force of attraction, only interact when they collide
• no definite shape or volume, will fill a container - bounce off walls and exert a pressure
• more energy than solid and liquid state
• hotter gases move faster, expand or pressure increases when heated

Question 9

What is sublimation?

Answer 9

Solid - gas

Question 10

What happens in melting?

Answer 10

• Solid is heated and gains more energy - increases vibration which weakens the intermolecular forces causing expansion - the particles gain enough energy to break free from their positions

Question 11

What happens in evaporation?

Answer 11

Particles gain energy - increases particle movement - weakens and breaks the bonds holding the liquid together - turns to gas

Question 12

What are the reactants of a reaction?

Answer 12

The substances you start off with

Question 13

What are the products of a reaction?

Answer 13

The substances made in a reaction

Question 14

How can substance purity be tested?

Answer 14

Using melting points - pure substances have specific sharp melting/boiling points - where as impure substances melt over a range of temperatures

Question 15

Define a pure substance

Answer 15

A substance made up entirely of a single element or compound

Question 16

How can melting points be used to test for purity of a substance?

Answer 16

Pure substances have specific, sharp melting and boiling points - mixtures will melt gradually over a range of temperatures

Question 17

What is the method in paper chromatography?

Answer 17

• Draw a pencil line near the bottom of the paper (baseline)
• Put a spot of the mixture to be separated on the line
• Put some solvent in the beaker
• Dip the very bottom of the paper into the solvent, clip the paper in place with a rod
• Put some watch glass on top of the beaker to stop solvent from evaporating
• The solvent will run up the paper, when chemicals in the mixture dissolve in the solvent, they move up too
• Different chemicals will separate out forming spots at different places on the paper
• Remove the paper from the beaker and mark the distance the solvent has moved in pencil

Question 18

What does it mean if the mixture does move up the chromatography paper?

Answer 18

The mixture is insoluble

Question 19

What is the Rf value formula?

Answer 19

Rf = distance travelled by solute

distance travelled by solvent

Question 20

What is a chromatogram?

Answer 20

The piece of paper you end up with

Question 21

What do you do if the chemicals on your chromatogram are colourless?

Answer 21

• spray with locating agent

Question 22

What does the Rf value show?

Answer 22

The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent

Question 23

How can you tell if a substance is pure on a chromatogram?

Answer 23

A pure substance will move as one blob and won’t be separated by chromatography

Question 24

What is simple distillation used for?

Answer 24

For separating out a liquid from a solution (e.g. getting pure water out of seawater)

Question 25

Describe the apparatus in simple distillation

Answer 25

A distillation flask with seawater in, thermometer sticking out top, connected to condenser with rubber tubing to keep it cool, a beaker to collect the pure liquid at the other end of the condenser, bottom end of condenser is connected to a tap using rubber tubing and cold water is run through the condenser in and out of the little gaps pumped upwards to keep it cool

Question 26

Describe the method of simple distillation (pure water from seawater)

Answer 26

- Pour sample of seawater into distillation flask - Set up the apparatus - Connect the bottom end of condenser to a cold tap using rubber tubing and run water through condenser to keep it cool - Gradually heat distillation tank, the part of solution with the lowest boiling point will evaporate (in this case the water) - The (water) vapour passes into the condenser where it cools and condenses and then flows into the beaker where it is collected - eventually, only the salt will be left in the flask

Question 27

What is the problem with simple distillation?

Answer 27

It can only be used to separate things with very different boiling points

Question 28

What is fractional distillation used for?

Answer 28

Separating a mixture of liquids (like simple distillation but with a fractionating column fitted between the distillation flask and the thermometer)

Question 29

Describe the method of fractional distillation (crude oil)

Answer 29

- Pour mixture into flask, attach a fractionating column (filled with glass rods) and condenser above the flask - Gradually heat the flask, the liquids will have different boiling points so will evaporate at different temperatures - The liquid with lowest boiling point evaporates, when the temperature on the thermometer matches the boiling point of the liquid, it will reach the top of the column - Liquids with higher boiling points may start to evaporate but the column is cooler at the top so they will only get half way before condensing back into the flask - When the first liquid has been collected, raise the temperature until the next one reaches the top - continue this until all liquids have been collected

Question 30

Why must water used in chemical analysis not contain dissolved salts?

Answer 30

They may interfere with reactions and give your experiment a false result - deionised water must be used

Question 31

What is deionised water?

Answer 31

Water that has had the ions that are present in normal tap water removed

Question 32

Where do we get potable water from (drinkable)?

Answer 32

- Surface water (lakes, rivers and reservoirs -start to run dry in summer) - Ground water (aquifers - rocks that trap water underground) - Waste water (contaminated by a human process e.g. as a by-product of industrial processes - treated to make it potable - preferable to disposing it which can be polluting)

Question 33

What are the steps needed to make fresh water suitable for drinking?

Answer 33

- Filtration - Sedimentation - Chlorination

Question 34

What happens in filtration of water?

Answer 34

A wire mesh screens out large twigs etc and then gravel and sand bed filter out other solid bits

Question 35

What happens in sedimentation of water?

Answer 35

Iron/aluminium sulfate is added to the water which clumps fine particles together and settle at the bottom

Question 36

What happens in chlorination of water?

Answer 36

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

Question 37

How can potable water be produced from sea water?

Answer 37

Using distillation - very expensive as uses a lot of energy especially in large quantities of water - used in dry countries but not uk

Question 38

What is a standard reference material?

Answer 38

a sample of a pure substance used in chromatography to compare to a solvent in an impure sample (to check if its the same type i think)

Question 39

What are the 2 phases of chromatography?

Answer 39

- mobile phase (where molecules can move - always a liquid or gas) - stationary phase (where the molecules can't move - can be a solid or thick liquid - the components in a mixture separate out and they end up in different places in the stationary phase as each chemical will spend a different amount of time dissolved in the mobile phase and stuck to the stationary phase - how fast it moves depends on how it distributes itself between phases)

Question 40

What is the stationary phase in paper chromatography?

Answer 40

a piece of filter paper

Question 41

What is the mobile phase in paper chromatography?

Answer 41

a solvent

Question 42

Why does the amount of time molecules spent in the stationary/mobile stage vary?

Answer 42

- molecules with a higher solubility in the solvent spend more time in the mobile phase so will be carried further up the paper - molecules that are more attracted to the stationary phase will not move as far