Year 9 Cambridge Science

1. Chapter 5 :
REACTIVITY

2. 5.1 Reactivity
and
displacement
reactions
Reactivity series

5. Metal
with
oxygen
Metal with
water

6. Metal
with
acid

7. Displacement
reaction
Example 1
Copper sulfate + iron > iron sulfate + copper
Iron is more reactive than copper. Iron displace copper.
Copper covers the iron strip. Blue copper sulfate solution changes to
paler color
But if copper metal put into iron sulfate – no reaction

8. • Example 2
Copper + silver sulfate >
copper sulfate + silver
Copper is more reactive
than silver. Silver metal
formed – settle on copper
wire

9. 5.2 Using displacement reaction
Extracting metals in industry
Example: extracting iron
Use metal that is more reactive than iron, e.g. Aluminium
Aluminium + iron oxide > aluminium oxide + iron
This reaction need to be ignited (by heat). The reaction itself
will produce a lot of heat (exothermic), thus, the iron
produced is in molten form.
- Welding railway –the molten iron produced is shaped to
join the rails together

10. Extract metal
from ores
• Example 2: Using
carbon to extract metals
from ores
• Ores are rocks that
contain metal compound
(copper oxide. Zinc
oxide, iron oxide …)
• Eg :Iron oxide + carbon
> Iron + carbon dioxide

12. 5.3 Salts
Few methods making salt
Method 1 : Using acid
Salt formed from acid has its name
end with –ate, -ide
Acid + metal > salt + hydrogen
e.g – sodium + hydrochloric acid >
sodium chloride + hydrogen (word
equation) – symbol equation?

14. Crystallization of
salt

15. • Method 2: Using metal oxide
Metal oxide + acid > salt + water
E.g.

16. • Method 3: Using carbonates and acid
Carbonates itself are salts – formed by carbonic acid with metal
Carbonates can form other salts by reacting with acid
Carbonates + acid > salt + water + carbon dioxide
e.g. hydrochloric acid + calcium carbonate > calcium chloride +
water + carbon dioxide
Limestone is made of calcium carbonate. Skeletons of coral in the
sea also are of calcium carbonate. When it react with acid, it
produces carbon dioxide that dissolve in the sea making it slightly
acidic. The salt produced (calcium chloride), make the water salty.

17. Hydrochloric acid + Magnesium carbonate >
magnesium chloride + water + carbon dioxide
MgCO3(aq) + 2HCl(aq) → MgCl2(aq) + CO2(aq) +
H2O(l)

18. • Method 4: Using acid and alkali (neutralization)
Acid + alkali > salt + water
E.g. sodium hydroxide + hydrochloric acid >
sodium chloride + water
NaOH(aq)+HCl(aq)→NaCl(aq)+H2O(l)

20. Difference between base and alkali
• Both are low in pH, react with acid to form salt
(neutralization)
• Base are solid, when it dissolves in water, it
forms alkali
• Metal oxides are bases. If it solubilize in water, it
forms alkali, for example sodium oxide.
• Some oxides are not soluble in water : copper
oxide

21. 5.5 Rearranging atoms
• In chemical reactions, atoms rearrange themselves
to form new compounds
• No atom were lost, nor any new ones produced
• Example: hydrochloric acid + zinc → zinc chloride + hydrogen
2HCl + Zn → ZnCl2 + H2
All elements in the reactants also present in the
products, nothing new produced, and nothing lost

22. Conservation of mass
• Look at page 196, who is correct?
• The mass you begin with in a chemical
reaction is the mass you end up with.
Nothing is lost nor added. This is the
law of conservation of mass
But, see page 198, if ..…
Calcium carbonate + hydrochloric acid >
Calcium chloride + water + carbon
dioxide
Why mass decrease?

23. • Heating magnesium cause
mass increase?
1. Weight magnesium in the
crucible
2. Heat up, open the lid
from time to time
3. All magnesium will turn
to ash
4. Weight them again
Magnesium + oxygen >
magnesium oxide

24. Exothermic and endothermic reaction
• Energy is involved in all chemical reaction.
• It is used to break bonds between elements in the compound, and
when new compound is formed, energy is released
• Exothermic – energy that released when forming new bonds in the
products is more than the energy which break bonds in the reactants.
e.g. sodium in water: sodium + water > sodium hydroxide + hydrogen
Fizzes vigorously and flames formed.
• Endothermic – energy taken in to break bonds in the reactants is
higher than the energy released when forming new bonds in the
products
E.g. Sodium hygencarbonate + citric acid (candy) > sodium citric +
water + carbon dioxide