Introduction - 3.1

Question 1

What are good words to use when describing substances in practical work?

Answer 1

• solid, liquid or gas?
• coloured or colourless?
• crystalline or powdered? (for solids)
• clear or cloudy? (for liquids)

Question 2

What are observations to make when describing changes during practical work?

Answer 2

• is there any fizzing
• has a solid appeared or disappeared
• has anything changed colour
• are there any unusual sounds or smells

Question 3

In general physical changes:

Answer 3

• create no new substances
• are usually easy to reverse
• absorb or release small amounts of energy

Question 4

In general, chemical changes:

Answer 4

• create new substances
• are usually difficult to reverse
• absorb or release large amounts of energy

Question 5

What is the chemical test for water?

Answer 5

anhydrous copper sulphate: turns from white to blue
- this tells you water is present not how pure it is

Question 6

What are the two physical tests for water?

Answer 6

• Melting point = 0 degrees C
• Boiling point = 100 degrees C

purer water matches these properties more closely

Question 7

What is the definition of an element?

Answer 7

an element is a substance containing one type of atom

Question 8

Elements: Metal vs Non-metal properties

Answer 8

Metal
- High MP/BP
- electrical conductors
- malleable
- shiny

Non-metal
- Low MP/BP
- electrical insulators
- brittle
- dull

Question 9

What is the definition of a compound?

Answer 9

a compound is a substance containing more than one type of atom that are chemically bonded together

Question 10

How can compounds be formed?

Answer 10

compounds can often be formed by heating their compounds together

Question 11

What are the properties of compounds?

Answer 11

The properties of a compound are usually totally different from the properties of the elements the compound is made from.
e.g. sodium chloride

Question 12

What are the types of compounds?

Answer 12

Metals
- metallic
Non-metals
- covalent
Both
-ionic

Question 13

Key practical: Ammonium Chloride Tube

Answer 13

Two gases, ammonia and hydrogen chloride diffuse from the ends of the sealed tube.
Where they meet, the compound ammonium chloride forms as a white smoke:
Ammonia + Hydrogen chloride → Ammonium chloride
This shows that the hydrogen chloride molecules must be heavier, as they diffused slower.

Question 14

Solute

Answer 14

The substance which is going to be dissolved

Question 15

Solvent

Answer 15

The liquid which is going to do the dissolving

Question 16

Solution

Answer 16

The resulting mixture of solute dissolved in solvent

Question 17

Saturated

Answer 17

A solution in which no more solute can be dissolved

Question 18

Suspension

Answer 18

A solid floating in a liquid because it cannot dissolve

Question 19

Soluble

Answer 19

A substance which can be dissolved

Question 20

Insoluble

Answer 20

A substance which cannot be dissolved

Question 21

What are the three key parts of a solubility curve?

Answer 21

• the line = saturated
  shows the maximum mass of solid which can be dissolved at each temperature
• below = soluble
  less than the maximum mass of solid, so it will all dissolve
• above = insoluble
  More than the maximum mass of solid, so some will dissolve and some won’t. The mass that dissolves can be found by reading off the line.