Elements, Compounds and Mixtures

Question 1

What are elements?

Answer 1

Substances that can’t be split into anything simpler by chemical methods and only contain one type of atom

Question 2

What are compounds?

Answer 2

When 2 or more elements chemically combine in a fixed ratio

Question 3

What are mixtures?

Answer 3

When various substances are mixed and don’t chemically react

Question 4

What is the difference between pure substances and mixtures?

Answer 4

Pure substances have a fixed melting and boiling point, whereas mixtures may melt or boil over a range of temperatures

Question 5

What is filtration used for?

Answer 5

To separate a solid from a mixture or two solids if one of them is soluble in water

Question 6

What is crystallisation used for?

Answer 6

To separate a solute from a solution

Question 7

How is crystallisation done?

Answer 7

The solution is heated in an evaporating basin to boil off some solvent until an almost saturated solution is formed. This can be tested by dipping a glass rod in the solution and seeing if crystals form quickly. The crystals can be removed from the mixture by filtration

Question 8

What is simple distillation used for?

Answer 8

To separate the components of a solution

Question 9

What is fractional distillation used for?

Answer 9

To separate a mixture of liquids

Question 10

What is paper chromatography used for?

Answer 10

To separate a variety of mixtures such as ink or food colouring

Question 11

How is paper chromatography done?

Answer 11

1. Draw a line with a pencil across a piece of chromatography paper about 1cm from the bottom. Don’t use pen because the ink may move with the solvent
2. Put a spot of dye onto the paper and allow it to dry
3. Set up the apparatus as shown
4. When the solvent front is about 1cm from the top of the paper, remove the paper from the breaker and draw a pencil line to show where the solvent got to
5. Leave the paper to dry so that all the solvent evaporates