C2.1

Question 1

What is relative atomic mass

Answer 1

Relative atomic mass is the mean mass of an atom compared to 1/12 the mass of a carbon 12 atom.

Question 2

What is relative formula masss

Answer 2

Relative formula mass (Mr) is the mean mass of a unit of a substance compared to1/12 of the mass of a carbon 12 atom.

Question 3

What is an empirical formula

Answer 3

An empirical formula shows the simplest whole number ratio of the atoms of each element in a compound.

Question 4

What does a balanced chemical equation show

Answer 4

A balanced chemical equation shows the formulae and number of units for all the substances in a reaction.

Question 5

What does a pure substance consist of

Answer 5

A pure substance consists of just one element or compound.

Question 6

Are mixtures pure or impure

Answer 6

Mixtures are impure as they contain more than one element or compound.

Question 7

Why are mixtures useful

Answer 7

Mixtures are useful because they contain the properties of all the substances that are in them.

Question 8

What is the melting point of a pure susbtance

Answer 8

The melting point of a pure substance is a single temperature.

Question 9

What happens if a substance is impure

Answer 9

If a substance is impure then the melting point is less than that of a pure substance. The substance also melts over a range of temperatures not just one.

Question 10

How do you determine the melting point of substances

Answer 10

You determine the melting point of a substance by heating it. You then measure its temperature at regular time intervals and then plot a graph.

Question 11

How do you make the process to find melting points more accurate

Answer 11

Heat it slowly
Stir the substance as it melts

Question 12

What is a solute

Answer 12

The substance that dissolves

Question 13

What is a solvent

Answer 13

The substance it is dissolved in

Question 14

What does filtration do

Answer 14

Filtration separates an insoluble substance in the solid state from substances in the liquid state. It works because, the filter paper has small holes in it that the liquid pass through but not the insoluble substance.

Question 15

What is the equipment needed for filtration

Answer 15

A funnel, a conical flask and filter paper.

Question 16

What are the substances that are separated in filtration

Answer 16

The residue is the insoluble substance and collects in the filter paper.
The filtrate can pass through the filter paper and collects in the conical flask

Question 17

What is crystallisation

Answer 17

Crystallisation is when you heat a solution and the solvent evaporates leaving the solute behind and if you allow the solvent to evaporate slowly you get regularly shaped crystals.

Question 18

What is needed for crystallisation to occur

Answer 18

For crystallisation to occur you need to heat the solution slowly until it becomes a saturated solution (no more solute can be dissolved in the solvent at that temperature) crystals will the start to form.

Question 19

What is the equipment needed for crystallisation

Answer 19

An evaporating basin, a beaker with water, the solution and bunsen burner

Question 20

What does simple distillation do

Answer 20

Simple distillation separates a solvent from a solution. It relies on the solvent having a much lower boiling point than the solute. When the solution is heated the solvent boils but the solute doesn’t. The solvent escapes in the gas state and is condensed back into liquid by the condenser.

Question 21

What is the equipment needed for simple distillation

Answer 21

A condenser, test tube, thermometer and conical flask

Question 22

What is fractional distillation

Answer 22

Fractional distillation separates two or more substances from a mixture in the liquid state. It relies on each state having a different boiling point and uses a fractionating column.
In the fractionating column:
. the water vapour condenses on the inside surface heating it up
. when the temperature inside reaches the lowest boiling point of one of the liquids, it can’t condense anymore so it passes into the condenser whereas the other liquid falls back into the flask.

Question 23

What is the equipment needed for fractional distillation

Answer 23

Fractionating column, conical flash, beaker, thermometer, condenser

Question 24

What does chromatography rely on

Answer 24

Chromatography relies on two different chemical phases.
. a stationary phase that doesn’t move
. a mobile phase that does move

Question 25

How do scientists compare the different values

Answer 25

They use the Rf values.

Question 26

How is gas chromatography different to paper and thin layer chromatography

Answer 26

Its different as the mobile phase is an unreactive carrier gas and the stationary phase is silica or alumina powder.

Question 27

Why do substances take different times to pass through

Answer 27

Because it depends on how attracted it is to the stationary and mobile phase.

Question 28

Rf formula

Answer 28

Rf = distance travelled by substance/distance travelled by solvent

Question 29

When the mixture contains an insoluble and soluble substance what do you do

Answer 29

Dissolving followed by filtration

Question 30

When the mixture contains a solute dissolved in a solvent what do you do

Answer 30

Crystallisation to obtain the solute or simple distillation to obtain the solvent

Question 31

When the mixture contains two or more substances in the liquid state

Answer 31

Fractional distillation

Question 32

When the mixture contains a coloured soluble substance

Answer 32

Paper chromatography or thin layer chromotography

Question 33

What are the benefits of paper chromatography

Answer 33

It is quicker
It is more sensitive so smaller samples can be used
There is a larger range of stationary phases and solvents to use