1.3 Separating Mixtures

Question 1

What does a mixture mean?

Answer 1

A mixture is made up of two or more substances (elements or compounds) that are not chemically combined together.

Question 2

Why is separating mixtures important in scientific terms in forensics or medical investigation?

Answer 2

When analytical chemists working on forensic or medical investigations are given an unknown sample to identify. This is often give a mixture of different substances.

Question 3

What are the properties of compounds?

Answer 3

• Compounds have a fixed composition.
• Chemical reactions must be used to separate the elements in a compound.
• Chemical bonds between atoms of different elements in the compound

Question 4

What does composition mean?

Answer 4

Ratio of elements present is always the same in any particular compound.

Question 5

What are the properties of mixtures?

Answer 5

• Mixtures have no fixed composition. This varies depending on the amount of each substance mixed together.
• Different elements or compounds in a mixture can be separated again more easily.
• There are no chemical bonds between atoms of the different substances in a mixture.

Question 6

What are the different methods of separation?

Answer 6

• filtration
• crystallisation
• distillation
• crhomatography

Question 7

What do the different separation methods rely on?

Answer 7

• Differences in physical proper tires of the substances in the mixture
• Different solubility in a solvent
• Different boiling points.

Question 8

What does filtration mean?

Answer 8

The technique to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent.

Question 9

What equipment involves with filtration?

Answer 9

• Beaker
• Filter paper
• Filter tunnel

Question 10

Example:

How would you separate a mixture of sand , salt (sodium chloride and water) using the method of filtration?

Answer 10

1) Pour the solution inside the beaker
2) The sand collected on the filter paper can be washed with distilled water to remove any salt solution left
3) Rest is the salt solution (the filtrate)

Question 11

How can you get pure , dry sand from the wet sand?

Answer 11

Wet sand is finally dried in a warm oven to evaporate any water off

Question 12

Example:

How would you obtain pure salt (sodium chloride and separate the solution(filtrate) from the water?

Answer 12

1) Put the salt solution in the evaporating dish over the beaker full of water. This is placed over the bunsen burner.
2) Heating should stop when the point of crystallisation
3) Rest of water is left to evaporate the saturated solution at room temperature to get sodium chloride crystals.

Question 13

What equipment is involved in the crystallisation process?

Answer 13

• Evaporating dish
• Beaker full of water
• Tripod
• Bunsen burner

Question 14

How can you tell that the crystallisation happens?

Answer 14

• Small crystals appear around the edge of the solution / crystals appear in a drop of solution extracted from the dish with a glass rod.

Question 15

What is crystallisation?

Answer 15

Separates a soluble solid from a solvent

Question 16

What is distillation?

Answer 16

When collecting the solvent itself instead of letting it evaporate off into the air.

Question 17

What is the advantage of using distillation?

Answer 17

Example:

Some countries that have a lack of fresh water sources , purify sea water to obtain usable water.

Question 18

What is the process of distillation?

Answer 18

1) Solution is heated and boiled to evaporate the solvent
2) Vapour given off then enters a condenser
3) The outer glass tube with water flowing acts cooling around the inner glass tube from the flask.
4) The hot vapour is cooled and condensed back into liquid for collection in receiving vessel.

Question 19

What equipment are involved in distillation?

Answer 19

• Heat
• Thermometer
• Condenser (water in , water out)
• Beaker