Seperation Techniques

Question 1

Give the definition of a pure substance

Answer 1

Has only one element or compound

Question 2

Give a definition of a mixture

Answer 2

Contains two or more different substances, not chemically joined together

Question 3

Give a definition of a compound

Answer 3

Contains two or more types of atom joined together

Question 4

Give an example of a pure element

Answer 4

Oxygen

Question 5

Give an example of a compound

Answer 5

Carbon dioxide

Question 6

Give an example of a mixture of elements

Answer 6

Oxygen and helium

Question 7

Do pure substances have sharp or a range of melting points?

Answer 7

Sharp

Question 8

Do mixtures melt at a sharp or have a range of melting points?

Answer 8

Range of melting points

Question 9

What is filtration used to do?

Answer 9

Separate an insoluble solid from a liquid

Question 10

What does insoluble mean?

Answer 10

Unable to dissolve in a particular solvent eg. Sand in water

Question 11

Why does filtration work?

Answer 11

The filter paper has tiny holes, or pores in it- large enough to let small molecules and dissolved ions through but not larger particles

Question 12

What is crystallisation used to produce?

Answer 12

Solid crystals from a solution

Question 13

Give how you can obtain crystals from crystallisation

Answer 13

-put solution in an evaporation basin
-warm the solution by placing the evaporating basin over a boiling water bath
- stop heating before all the solvent has evaporated
- after cooled, dry the crystals using a warm oven or in air

Question 14

What is simple distillation used to separate?

Answer 14

A solvent from a solution- producing water from a salt solution

Question 15

Why does simple distillation work?

Answer 15

The dissolved solute has a much higher boiling point than the solvent- the solvent evaporated from the solution, is cooled and condensed

Question 16

What’s fractional distillation used to separate?

Answer 16

Different liquids from a mixture of liquids

Question 17

Why does fractional distillation work?

Answer 17

The different liquids have different boiling points

Question 18

Give how liquids are collected from fractional distillation

Answer 18

-vapour rises through a column which is hot at the bottom-cold at the top
-vapour condenses when they reach a part of the column that’s below the temp of their boiling point
-the liquid flows out of the column

Question 19

What is paper chromatography used to separate?

Answer 19

Mixtures of soluble substances- food dye

Question 20

Give the two phases of chromatography

Answer 20

Stationary phase
Mobile phase

Question 21

Give what happens during the stationary phase

Answer 21

Very uniform, absorbent paper

Question 22

Give what happens during the mobile phase

Answer 22

The solvent that moves through the paper, carrying different substances with it

Question 23

How do you know if a substance is pure on a chromatogram?

Answer 23

Has one spot on the chromatogram

Question 24

How do you know if a substance is impure on a chromatogram?

Answer 24

Produces two or more spots

Question 25

Give the calculation for Rf value

Answer 25

Distance traveled by substance / distance travelled by solvent

Question 26

What does potable mean?

Answer 26

Safe to drink

Question 27

What is the aim for investing the compositions of ink practical?

Answer 27

To investigate the compositions of inks using simple distillation and chromatography

Question 28

Give the hazards and harm for the practicals for the ink practical

Answer 28

Bunsen burner- skin burns/fire
Harmful solvent- skin irritation/ breathing difficulty