This is a powerpoint presentation about chemical changes, directly following the specification of igcse oxford aqa

1. CHEMICAL CHANGES
REVISION LESSON

2. METALS: REACTIVITY SERIES

3. METALS ARE USEFUL BECAUSE…
• They are good conductors of
• Heat
• Electricity
• Why?
• Because they have free/delocalized
electrons
• When heated, the delocalized electrons
gain more energy and move faster,
colliding with neighboring electrons and
metal ions. Heat is thus transferred
throughout the metal.
• They can be
• Bent
• Hammered into shape
• Why?
• Because the layers of atoms are able to
slide over each other

4. ALLOYS
• An alloy is a mixture of at least two
elements, at least one of is a metal.
• Alloys often have properties that are
different from the metals they contain,
making them more useful than the pure
metals alone.
• Steels are a mixture of iron with carbon and
sometimes other metals.

5. COPPER IS USEFUL FOR…
 Electrical wiring
• It is a good conductor of heat and
electricity
 Plumbing
 It can be bent but is hard enough to
be used to make pipes or tanks
 It does not react with water

6. THE REACTIVITY
SERIES
• Metals can be arranged in
order of reactivity from
their reactions with water
or dilute acids.
Perhaps making
a mnemonic
from this could
help

7. DISPLACEMENT IN THE REACTIVITY SERIES
• Try and complete this ionic equation
2
+
0 2
+ 0
Which metal is being:
Reduced?
Oxidized?

8. ANSWERS
• Copper is reduced • Zinc is oxidised

9. EXTRACTING GOLD
Gold is unreactive
Found on Earth as metal itself
Most metals are found as
compounds that require
chemical reactions to extract
the metal

10. EXTRACTING IRON
• Metals that are less reactive than carbon can be extracted from their oxides by
reduction with carbon:
• For example, iron oxide is reduced in the blast furnace to make iron.
• Carbon is more reactive than iron, so it can displace iron from iron(III) oxide.
Here are the equations for the reaction:
• Iron(III) oxide + carbon → iron + carbon dioxide
• 2Fe2O3(s) + 3C(s) → 4Fe(l) + 3CO2(g)
• In this reaction, the iron(III) oxide is reduced to iron, and the carbon
is oxidised to carbon dioxide.

11. EXTRACTING COPPER
• New ways of extracting copper from low-grade
ores are being researched to limit the
environmental impact of traditional mining
• Some examples of these include:
• Phytomining
• phytomining uses plants to absorb
metal compounds and that the
plants are burned to produce ash
that contains the metal compounds
• Bioleaching
• bioleaching uses bacteria to
produce leachate solutions that
contain metal compounds

12. EXTRACTING COPPER (CONTINUED):
ELECTROLYSIS
• Copper can be obtained from
solutions of copper salts by
electrolysis.
• This electrolysis involves graphite
electrodes
• When electrolyzing copper sulphate
solution, copper is reduced:
• Cu2+
(aq) + 2e– ==> Cu(s)
• Oxygen is oxidized:
• 4OH- → O2 + 2H2O +4 2e
This is a
required
practical!

13. EXTRACTING COPPER (CONTINUED)
DISPLACEMENT
• Copper can be obtained from solutions of
copper salts by displacement using scrap iron.
• Iron is more reactive than copper. It
can displace copper from the leachate. For
example:
• iron + copper sulfate → iron(II) sulfate + copper
• Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
• Cu2+
(aq) + 2e– ==> Cu(s)
• Fe(s) ==> Fe2+
(aq)+ 2e–
• Since iron is cheaper than copper, the use of
scrap iron is a cost-effective way to produce
copper from the leachate.

14. RECYCLING METALS
We should recycle metals
because extracting them
uses limited resources, and
is expensive in terms of
energy and in terms of
effects on the environment

15. METALS: METAL CARBONATES

16. METAL CARBONATES
THERMAL DECOMPOSITION
• The carbonates of magnesium, copper,
zinc, calcium and lithium decompose on
heating (thermal decomposition) in a
similar way.
• Not all carbonates of metals in Group 1 of
the periodic table decompose at the
temperatures reached by a Bunsen
burner.
• Metal carbonate = metal oxide + carbon
dioxide

17. METAL CARBONATES: CONTINUED
• Metal carbonates react with acids to produce carbon dioxide, a
salt and water
• Metal carbonate + acid = carbon dioxide + salt + water
• H2SO4(aq)+CaCO3(aq)→CaSO4(s)+CO2(g)+H2O (l)
• Since there is carbon dioxide as one of the products, we can
bubble some of this CO2 (using a delivery tube and a bung) into
limewater and it should turn cloudy

18. ELECTROLYSIS

19. IONIC COMPOUNDS AND ELECTROLYSIS
• When an ionic substance is melted or dissolved in water, the ions are free to
move about within the liquid or solution (and thus carry the current).
• Passing an electric current through ionic substances that are molten, e.g. lead
bromide, or in solution breaks them down into elements.
• This process is called electrolysis and the substance broken down is called the
electrolyte.

21. BREAK DOWN OF ELECTROLYSIS
• At the cathode, positively charged ions gain electrons.
• Reduction
• At the anode, negatively charged ions lose electrons.
• Oxidation
• If there is a mixture of ions:
• at the cathode, the products formed depend on the reactivity of the elements
involved
• at the anode, the products formed also depend on (both reactivity and) the relative
concentrations of the ions present

22. ELECTROLYSIS AND ELECTROPLATING
• Electrolysis can be used to
electroplate objects.
• This may be for reasons such as:
• Appearance
• Durability
• Prevention of corrosion
• It includes copper plating and
silver plating.

23. EXTRACTING
ALUMINIUM
• Aluminium is manufactured by the electrolysis of a molten
mixture of aluminium oxide and cryolite
1. Aluminium ore is called bauxite. The bauxite is purified
to produce aluminium oxide
2. The ions in the aluminium oxide must be free to move
so that electricity can pass through it.
3. Aluminium oxide has a very high melting point (over
2000°C) so it would be expensive to melt it because of
the large amounts of energy needed in the extraction
process
1. so we dissolve it in molten cryolite.
4. The use of cryolite reduces some of the energy costs
involved in extracting aluminium.
5. Aluminium forms at the negative electrode and oxygen
at the positive electrode
6. The positive electrode is made of carbon, which reacts
with the oxygen to produce carbon dioxide

24. ELECTROLYSIS OF SODIUM CHLORIDE
• The electrolysis of sodium chloride (aq) results
in the following ions:
• Na+
• Cl-
• H+
• OH-
• Both the Na+ and H+ ions go to the cathode
(negatively-charged), but the hydrogen is
electrolyzed because Na+ is too reactive. This
makes hydrogen gas bubble around the
cathode.
• 2H+(aq) + 2e- → H2(g)
• Both OH- and Cl- ions go to the anode
(positively-charged), but the Cl- is
electrolyzed, making chlorine gas around
the anode.
• 2Cl-(aq) → Cl2(g) + 2e-
• Na+ and OH- ions are left behind, making
NaOH (sodium hydroxide)
• NaOH can then be used to produce bleach
and plastics
• Cl is used to sterilise water supplies, and
to make bleach and hydrochloric acid
• H is used as a fuel and for making
ammonia.

25. DONE!
Thanks for listening 