Separation and Purification

Question 1

What is a mixture? Examples?

Answer 1

Made up of two or more substances that are not chemically combined

Mineral water
Air
Stainless steel
Orange juice

Question 2

What is a pure substance? Examples?

Answer 2

Made up of one single element or compound. It is not mixed with any other substance

Nitrogen gas
Sodium chloride crystal
Mercury liquid
Pure water

Question 3

How to determine whether a substance is pure?

Answer 3

1. Fixed melting point

2. Fixed boiling point

Question 4

Impurities affects

Answer 4

1. Impurities lower the melting point and cause the substance to melt over a range of temperatures
2. Impurities raise the boiling point and cause the substance to boil over a range of temperatures

Question 5

What is filtration?

Answer 5

Used to separate insoluble solid particles from a liquid

Sand and water
Chalk and water

Question 6

What is a residue?

Answer 6

The solid that remains on the filter paper

Question 7

What is a filtrate?

Answer 7

The liquid that passes through the filter paper

Question 8

What is evaporation to dryness? And stuff + caution

Answer 8

Used to obtain a soluble solid from a solution by heating the solution until all the water has been boiled off

The solid obtained will not always be pure

Not suitable for solids that decompose upon heating

Safety goggles must be worn as very hot concentrated liquid can sputter from the dish

Salt and water
Sugar and water

Question 9

What is crystallisation?

Answer 9

Used for obtaining a pure solid sample from its solution

Question 10

Steps of crystallisation

Answer 10

1. Heat the solution to saturation point
2. Allow solution to cool, crystals will form
3. Wash the crystals with deionized water
4. Dry the crystals between sheets of filter paper

Question 11

What is simple distillation? Why are boiling chips added?

Answer 11

Used to separate a pure solvent from a liquid

Ensures smooth boiling

To recover water from seawater
To extract water from sodium chloride solution

Question 12

What is fractional distillation?

Answer 12

Used to separate a mixture of miscible liquids with different boiling points

Separate
Ethanol
Liquid air

Question 13

What is chromatography? Uses?

Answer 13

The method of separating two or more components that dissolve in the same solvent

Determine whether a sample is pure
Identify substances

Dyes
Pencil is used instead of pen because ink will dissolve in the solvent