Topic 2 - States of matter and mixture

Question 1

What are the properties of solids? (4)

Answer 1

• 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 positiors so all solids keep a definite shape and volume.
• The particles in a solid don’t have much energy.
• They hardly move at all- in fact, they can only vibrate about their fixed positions. The hotter the solid becomes, the more they vibrate (causing solids to expand slightly when heated).

Question 2

What are the properties of Liquids? (4)

Answer 2

• There is some force of attraction between the particles. They’re free to move past each other, but they do tend to stick together.
• Liquids don’t keep a definite shape and will flow to fill the bottom of a container. But they do keep the same volume
• For any given substance, in the liquid state its particles will have more energy than in the solid state(but less energy than in the gas state).
• The particles are constantly moving with random motion. The hotter the liquid gets, the faster they move. This causes liquids to expand slightly when heated.

Question 3

What are the properties of Gases? (4)

Answer 3

• There’s next to no force of attraction between the particles -they’re free to move. They travel in straight lines and only interact when they collide.
• Gases don’t keep a definite shape or volume and will always fill any container. When particles bounce off the walls of a container they exert a pressure on the walls.
• For any given substance, in the gas state its particles will have more energy that in the solid state or the liquid state.
• The particles move constantly with random motion. The hotter the gas gets, the faster they move. Gases either expand when heated, or their pressure increases.

Question 4

What is the reaction from solid to liquid called?

Answer 4

Melting

Question 5

What is the reaction from liquid to gas called?

Answer 5

Evaporation

Question 6

What is the reaction from gas to liquid called?

Answer 6

Condensation

Question 7

What is the reaction from liquid to solid called?

Answer 7

Freezing

Question 8

What is the reaction from solid to gas called?

Answer 8

Sublimation

Question 9

What is the difference between a pure substance and a mixture?

Answer 9

A pure substance consists only of one element or one compound
A mixture consists of two or more different substances, not chemically joined together

Question 10

What are the different types of substance? (3)

Answer 10

• an ELEMENT contains just one type of atom
• a COMPOUND contains two or more types of atom joined together
• a MIXTURE contains two or more different substances that are not joined together

Question 11

Describe simple distillation

Answer 11

Simple distillation is used to separate a SOLVENT from a SOLUTION. It is useful for producing water from salt solution.

Simple distillation works because the dissolved solute has a much higher boiling point than the solvent. When the solution is heated, solvent vapour evaporates from the solution. The gas moves away and is cooled and condensed. The remaining solution becomes more concentrated in solute as the amount of solvent in it decreases.

Question 12

What is Fractional Distillation?

Answer 12

Fractional distillation is used to separate different liquids from a mixture of liquids. It is useful for separating ethanol from a mixture of ethanol and water, and for separating different fractions from crude oil.

Question 13

Describe the process of fractional distillation (3)

Answer 13

There’s a temperature gradient (it’s hotter at the bottom and gets colder than you go up). Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top. The substance is evaporated and its vapours condense at different temperatures in the fractionating column.

Question 14

What is Filtration?

Answer 14

Filtration is used to separate an insoluble solid from a liquid. It is useful for separating sand from a mixture of sand and water, or excess reactant from a solution.

Filtration works because the filter paper has tiny holes, or pores, in it. These are large enough to let small molecules and dissolved ions through, but not the much larger particles of undissolved solid.

Question 15

What is Crystallisation?

Answer 15

Crystallisation is used to produce solid crystals from a solution. When the solution is warmed, some of the solvent evaporates leaving behind a more concentrated solution.

Question 16

What two phases does chromatography rely on?

Answer 16

• the stationary phase, which in paper chromatography is very uniform, absorbent paper
• the mobile phase is the solvent that moves through the paper, carrying different substances with it

Question 17

How is a chromatogram created?

Answer 17

Separation by chromatography produces a chromatogram.

Question 18

What is the paper chromatogram used for?

Answer 18

A paper chromatogram can be used to distinguish between pure and impure substances:

• a pure substance produces one spot on the chromatogram
• an impure substance produces two or more spots

A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if:

• they produce the same number of spots, and these match in colour
• the spots travel the same distance up the paper (have the same Rf value)

Question 19

What are Rf values and what is it used for?

Answer 19

Distance travelled by substance.

Rf values can be used to identify unknown chemicals if they can be compared to a range of reference substances. The Rf value is always the same for a particular substance.

Question 20

Why must fresh water be made potable?

Answer 20

Fresh water contains objects that must be removed to make it potable. These include large objects such as branches and leaves, insoluble particles such as grit, and harmful microorganisms.

Question 21

How are different methods used to get out objects of all size in fresh water? (5)

Answer 21

1. Large objects are removed by screening using grids (filtration).
2. A coarse filter bed made from clean sand and gravel removes larger insoluble grit particles (filtration).
3. Aluminium sulfate is added to clump smaller insoluble particles together, which then settle to the bottom in a sedimentation tank (sedimentation).
4. A fine filter bed removes very small insoluble particles (filtration).
5. Chlorine gas is added to kill harmful microorganisms (chlorination).

Question 22

How is sea water purified?

Answer 22

Distillation, the seawater is boiled and the water vapour is led away and cooled. It condenses to form pure water, leaving the salt behind. Very expensive as a lot of energy is required to boil water to produce potable water.

Question 23

Why must the water be pure during chemical analysis?

Answer 23

So that ions such as calcium, iron and copper from in tap water doesn’t interfere with reactions. Normal water could give you a false result.

Question 24

Describe an investigation that investigates the composition of inks using simple distillation. (4)

Answer 24

1) Add a small volume of ink to a flask. Connect the flask to the fractionating column and secure it with a stand, boss and clamp.
2) Attach a condenser to the top of the fractionating column, connect it to a cold water tap and sink, and secure it over a beaker.
3) Heat the flask using a Bunsen burner, reducing the flame as necessary to achieve gentle simmering.
4) Collect a small sample of the distilled solvent, then turn the Bunsen burner off.

Question 25

What is Paper Chromatography?

Answer 25

Paper chromatography is used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.

The different dissolved substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper.

Question 26

Describe an investigation that investigates the composition of inks using chromatography. (5)

Answer 26

1) Draw a pencil line across the chromatography paper, 1-2 cm from the bottom
2) Use a pipette or capillary tube to add small spots of each ink to the line on the paper
3) Place the paper into a container with a suitable solvent in the bottom
4) Allow the solvent to move through the paper, but remove the chromatogram before it reaches the top
5) Allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent

Question 28

How do you conduct crystallisation? (5)

Answer 28

1) Put the solution in an evaporating basin
2) Warm the solution by placing the evaporating basin over a boiling water bath
3) Stop heating before all the solvent has evaporated
4) After the remaining solution has cooled down, pour the excess liquid away (or filter it).
5) Dry the crystals using a warm oven or in air.