Section 2 - States of matter and mixtures - Purification, chromatography and water treatment

Question 1

What is a pure substance?

Answer 1

A substance completely made up of a single element or compound

Question 2

What is simple distillation used for?

Answer 2

Separating out a liquid from a solution (e.g. pure water from sea water)

Question 3

What is fractional distillation used for?

Answer 3

Separating a mixture of liquids

Question 4

What is filtration used for?

Answer 4

Separating an insoluble solid form a liquid

Question 5

What is crystallisation used for?

Answer 5

Separating a soluble solid from a solution

Question 6

4 methods of purification?

Answer 6

Simple distillation, fractional distillation, filtration, and crystallisation

Question 7

What is chromatography used for?

Answer 7

Separating a mixture of soluble substances and identifying them

Question 8

Two phases in chromatography and what are they?

Answer 8

Mobile phase - where molecules can move. This is always a liquid or a gas
Stationary phase - where the molecules can’t move. This can be solid or really thick liquid

Question 9

In chromatography, why do the components in a mixture separate out as mobile phase moves over stationary phase and end up in different places?

Answer 9

Each of the chemicals in mixture spend different amounts of time dissolved in mobile phase and stuck to stationary phase

Question 10

In paper chromatography, what is the stationary phase and the mobile phase?

Answer 10

Stationary phase - piece of filter paper (chromatogram)

Mobile phase - Solvent

Question 11

Why should the baseline on a chromatogram in paper chromatography be drawn in pencil and not pen?

Answer 11

Pencil marks are insoluble and won’t move with solvent as ink might

Question 12

Two things the amount of time the molecules spends in each phase depend on in paper chromatography?

Answer 12

How soluble they are in solvent and how attracted they are to stationary phase

Question 13

What is the Rf value? Formula for Rf value?

Answer 13

The ratio between distance travelled by dissolved substance (solute) and distance travelled by solvent
Rf = distance travelled by solute ÷ distance travelled by solvent

Question 14

What is potable water?

Answer 14

Water that is fit to drink

Question 15

3 types of water sources?

Answer 15

Surface, ground and waste water

Question 16

3 processes in which water is purified in water treatment plants and what happens in each process?

Answer 16

Filtration - wire mesh screens out large twigs etc. then gravel and sand bends filter out any other solid bits
Sedimentation - iron- or aluminium- sulfate added to water to make fine particles clump together and settle at bottom
Chlorination - chlorine gas bubbled through to kill harmful bacteria and other microbes

Question 17

Con of distillation sea water to get potable water?

Answer 17

Distillation needs loads of energy so really expensive

Question 18

What is deionised water?

Answer 18

Water that has had the ions present in normal tap water removed