C2.1

Question 1

What is relative atomic mass?

Answer 1

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

Question 2

What is relative formula mass?

Answer 2

Relative formula mass, Mt, is the mean mass of a unit of a substance compared to 1/12 the mass of a carbon 12 atom.

Question 3

What does empirical formula show?

Answer 3

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

The formulae and number of units for all the substances in a reaction.

Question 5

What is a pure substance?

Answer 5

an element consisting of just one element or compound.

Question 6

What is a mixture?

Answer 6

A mixture is an impure substance, since they contain more than one element or compound.

Question 7

What is special about the melting point of a pure substance?

Answer 7

It is a single temperature

Question 8

What happens to the melting point if a substance is impure?

Answer 8

If a substance if impure, its melting point is less than a pure substance and it is over a range of temperatures.

Question 9

How does a solution form?

Answer 9

when one substance is dissolved in another.

Question 10

What is the solute?

Answer 10

The substance that dissolves

Question 11

What is the solvent?

Answer 11

The substance that the solute dissolves in.

Question 12

What does filtration do?

Answer 12

Filtration separates an insoluble substance in the solid state from another substance in the liquid state.

Question 13

How do you do crystallisation?

Answer 13

Heat a solution, let the solvent evaporate, leaving the solute behind. If you heat it too strongly, you get a powder, but if you allow the solvent to evaporate slowly, you get regularly shaped crystals.

Question 14

What is simple distillation?

Answer 14

Separates a solvent from a solution, when the solution is heated, the solvent boils but the solute doesn’t. The solvent evaporates, then is cooled and condensed by a condenser.

Question 15

What does fractional distillation do?

Answer 15

Separates two or more substances from a mixture in the liquid state.

Question 16

What are the stationary and mobile phases in paper chromatography?

Answer 16

stationary phase= absorbent paper and mobile phase= solvent in liquid state

Question 17

What are the stationary and mobile phases in thin layer chromatography?

Answer 17

Stationary phase=a thin layer of silica or alumina powder spread over a plate of glass or plastic.
mobile phase= solvent in liquid state.

Question 18

Describe gas chromatography

Answer 18

gas chromatography separates the components of a mixture and also measures their amounts. Stationary phase= silica/alumina powder packed into metal column and mobile phase= unreactive carrier gas(e.g: nitrogen)

Question 19

What is the formula for Rf

Answer 19

Rf= distance travelled by substance/ distance travelled by solvent

Question 20

Describe Rf values

Answer 20

Rf values always vary from 0 to 1 and have no units.

Question 21

Why is TLC better than paper chromatography?

Answer 21

its quicker, more sensitive(smaller sample used); larger range of solvents and stationary phase; can scrape dots for further analysis.

Question 22

What separation methods should be used if the mixture contains insoluble and soluble?

Answer 22

dissolving and filtration.

Question 23

What separation methods should be used if the mixture contains a solution?

Answer 23

crystallisation and simple distillation

Question 24

What separation methods should be used if the mixture contains 2 or more liquid substances?

Answer 24

fractional distillation

Question 25

What separation methods should be used if the mixture contains coloured soluble substances?

Answer 25

paper chromatography or thin layer chromatography.