3.1.1 - Introduction

Question 1

What are good observations to make when DESCRIBING SUBSTANCES in practical work ?

Answer 1

. Solid, liquid or gas ?
. Colored or colorless ?
. Crystalline or powdered ? (For solids)
. Clear or cloudy (for liquids)

Question 2

What are good observations to make when DESCRIBING CHANGES during practical work ?

Answer 2

. Is there any fizzing ?
. Has a solid appeared or disappeared ?
. Has anything changed color ?
. Are there any unusual sounds or smells ?

Question 3

In general physical changes…

Answer 3

. Create NO NEW SUBSTANCE

. Are usually EASY TO REVERSE

. Absorb or release SMALL AMOUNTS OF ENERGY

Question 4

An example of a PHYSICAL change :

Answer 4

. Melting ice in a beaker:
- the particles are still water particles they just move around more afterwards

• you can reverse it, put the water back in the freezer
• the beaker doesn’t get much hotter or colder

Question 5

I’m general, CHEMICAL changes…

Answer 5

. Create NEW SUBSTANCES

. Are usually DIFFICULT TO REVERSE

. Absorb or release LARGE AMOUNTS OF ENERGY

Question 6

An example of a CHEMICAL change :

Answer 6

. Burning wood on the floor:
- the wood and oxygen particles turn into soot

-it’s impossible to collect the soot and turn it back into wood

• the floor gets really hot !

Question 7

CHEMICAL test for water:

Answer 7

. Anhydrous copper (II) sulphate
- turns from white to blue ⬜️➡️🟦

Question 8

Disadvantage of using the CHEMICAL test for water ?

Answer 8

. It tells you water is present, but not how pure it is

Question 9

Two PHYSICAL tests for water:

Answer 9

• Melting point (MP)= 0*C
• Boiling point (BP) = 100*C

. Pure water MATCHES THESE PROPERTIES MORE CLOSELY