5.2 Separating Mixtures

Question 1

What is a pure substance?

Answer 1

All of its particles are the same.

Question 2

What is a mixture?

Answer 2

Contains 2 or more substances, which may be elements or compounds.

Question 3

How do you find out if a substance is pure?

Answer 3

A pure substance has a fixed melting and boiling point, its temperature stays at its melting point until all the solid has melted.

Question 4

What is a solution?

Answer 4

A mixture of a liquid with a solid or gas.

Question 5

What is a solvent?

Answer 5

The liquid something dissolves into.

Question 6

What is a solute?

Answer 6

What dissolves into the solvent when it is mixed.

Question 7

What is a saturated solution?

Answer 7

A solution that contains the maximum mass of a substance that will dissolve.

Question 8

What is solubility?

Answer 8

The maximum mass of the solute that dissolves in 100g of water.

Question 9

What does insoluble mean?

Answer 9

Substances that cannot dissolve - e.g. chalk and sand in water.

Question 10

What is a solubility curve?

Answer 10

A graph that shows how solubility of a solute changes depending on the temperature of the solvent. Most substances get more soluble as temperature increses.

Question 11

What is filtration?

Answer 11

A method of separating substances which separates a liquid or solution from an insoluble solid.

Question 12

How does filtering work?

Answer 12

You can separate some substances by pouring the mixture into filter paper. Filter paper has tiny holes in it, water particles are smaller than them so can pass through the holes. This is the filtrate. Something like sand cannot pass through so stays in the filter paper as residue.

Question 13

What are some uses of filtration?

Answer 13

• Separates coffee solution from ground up beans
• Oil filters in cars trap bits of dirt that would damage the engine if they stayed in the oil
• Sand filters help make water safe to drink.

Question 14

What are three uses of evaporation?

Answer 14

1. Obtaining lithium - huge amounts are dissolved in water under a desert in Bolivia.
2. To make crystals from solutions in a lab
3. To separate salt from seawater.

Question 15

What is distillation?

Answer 15

A separation method that uses boiling and condensing to separate substances with different boiling points.

Question 16

How does distillation work (separating seawater)?

Answer 16

• On heating, water in the solution boils, forming steam but the salt does not.
• Steam leaves the solution and travels through the condenser, cooling down.
• The steam condenses to form liquid water which drips into the beaker.

Question 17

What does chromatography do?

Answer 17

It separates dyes so you can find out which dyes make up colours.

Question 18

How does chromotography work?

Answer 18

Water moves up the chromatography paper and mixes with the dyes when it reaches the coloured spot. The mixture moves upwards and over time separates. Dyes that are attracted more strongly to the water than the paper travels further than other dyes, separating them. The separated dyes make a chromatogram.

Question 19

Why is chromatography useful?

Answer 19

You can use it to show the pigments in food. Each pigment is a different nutrient so you can compare different sorts of that food for their health benefits.