C2.1

Question 1

What is an empirical formula?

Answer 1

Shows the simplest whole number ratio of the atoms of each element in a compound
C4H10 = C2H5

Question 2

What does pure mean?

Answer 2

A substance that consists of just one element or compound

Question 3

What is an impure substance?

Answer 3

A mixture, as it contains more than one element or compound

Question 4

What is an alloy?

Answer 4

A mixture of a metal with one or more elements

Question 5

What is the melting point?

Answer 5

The temperature at which it changes from the solid to liquid state

Question 6

What is the melting point f a pure & impure substance?

Answer 6

Pure:
- melting point is a single temperature
Impure:
- melting point I less than that of the pure substance
- normally over a range of temperatures

Question 7

How to determine a melting point?

Answer 7

• by heating it and measuring the temperature it melts at
• heat the substance nd measure the temperature at regular time intervals and plot a graph

Question 8

What is a solution?

Answer 8

What forms when one substance dissolves in another

Question 9

What is a solute?

Answer 9

The substance that dissolves

Question 10

What is the solvent?

Answer 10

The substance the solute dissolves in

Question 11

What does filtration do?

Answer 11

Separates an insoluble substance in the solid state from substances in the liquid state

Question 12

How does filtration work?

Answer 12

Filter paper has tiny microscopic holes so when a mixture of water and sand is poured through, the water molecules are small enough to pass through but the insoluble sand remains as a residue and the water is the filtrate in the conical flask

Question 13

How does crystallisation work?

Answer 13

1) heat the solution gently until saturated (no more solute can be dissolved at that temperature)
2) as the solvent evaporates slowly crystals form
3) you can separate them from the solution with filtration

Question 14

What does does simple distillation do?

Answer 14

Separates a solvent from a solution

Question 15

How does simple distillation work?

Answer 15

Relies on the solvent having a lower boiling point than the solvent
1) heat the conical flask with a Bunsen burner
2) the solvent will boil but the solute won’t
3) the solvent escapes the solution in gas state
4) it is then cooled and condensed back into liquid state by the condenser
5) the liquid is then collected in a test tube after being purified

Question 16

What does fractional distillation do?

Answer 16

Separates two or more substances from a mixture

Question 17

How does fractional distillation work?

Answer 17

Relies on the substance having different boiling points:
1) the solution is heated by a Bunsen burner to the temperature of the lower boiling point
2) this substance will rise and evaporate first
3) the vapour will pass through the condenser where it cools and condenses and is collected into a beaker
4) the other substance will evaporate once the temperature increases to its boiling point

Question 18

Why is a fractional column used?

Answer 18

It improves the separation of the mixtures
Has a large SA for the vapour to condense on
The column is hottest at the bottom and coolest at the top

Question 19

What are the two phases chromatography?

Answer 19

Stationary phase - doesn’t move (absorbent paper)(thin layer of silica or alumina powder)
Mobile phase - does move (solvent)

Question 20

What is paper chromatography?

Answer 20

Used to separate coloured substances in ink or sweets

Question 21

How does thin layer chromatography work?

Answer 21

1) Put the solvent in a chromatography tank
2) add a small amount of the substance to the baseline
3) let the solvent travel through the powder and take the plate out before it reaches the top
4) analyse the pattern of the chromatogram

Question 22

What is the Rf value?

Answer 22

Used to compare different spots on a chromatogram
If two substances have the same Rf value they’re the same

Question 23

What is gas chromatography?

Answer 23

Used to separate a mixture of gases
Mobile phase = unreactive carrier gas
Stationary phase = unreactive liquid

Question 24

How does gas chromatography work?

Answer 24

1) mixture is injected into the column
2) mixture is carried by the carrier gas through the column
3) different substances in the mixture will take different James to travel through the column (depending on their attraction to the stationary phase)
4) as each component leaves the column a peak is plotted against travel time on a chromatogram generated by a computer

Question 25

How to interpret gas chromatogram?

Answer 25

Number of peaks = number of compounds in the mixture
Height of peak = how much of each compound is present
Position of peak = retention time of compound