Page 38 - Spotlight A+ Form 4 & 5 Chemistry KSSM

Form
5 Chemistry Chapter 1 Redox Equilibrium

CHAP. Results: CHAP.
1 Copper, Cu Table 1.27 1
strip
Tongs A Black layer formed on the brown copper strip.
Bunsen burner
B The grey iron wool turns into a reddish-brown
solid.

Figure 1.40 Inference:
1. Copper(II) oxide, CuO is formed.
B Burning of iron, Fe wool 2. Iron(II) oxide, Fe O is formed.
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2 3
Procedure:
1. A small amount of iron, Fe wool is placed in a Discussion:
combustion spoon. 1. Copper, Cu is oxidised to copper(II) oxide,
2. The iron, Fe wool is heated until it starts to CuO which is black in colour.
burn. 2Cu(s) + O (g) → 2CuO(s)
3. The burning iron, Fe wool is quickly lowered 2
2+
into a gas jar filled with oxygen gas, O as Cu → Cu + 2e –
2
shown in Figure 1.41. Copper atom, Cu releases two electrons
4. All observations are recorded. to form copper(II) ion, Cu . Copper, Cu
2+
undergoes corrosion.
Combustion
spoon
2. Iron, Fe is oxidised to iron(III) oxide, FeO
Gas jar
which is reddish-brown in colour.
Oxygen gas, O
4Fe(s) + 3O (g) → 2Fe O (s)
2
Iron, Fe wool 2 2 3
Fe → Fe + 3e –
3+
Iron atom, Fe releases three electrons to form
Figure 1.41 iron(III) ion, Fe . Iron, Fe undergoes corrosion.
3+

• Corrosion of copper, Cu and iron, Fe
Corrosion of copper, Cu and iron, Fe will occur at moist open atmosphere. Iron, Fe is more electropositive than
copper, Cu. Thus, iron, Fe corrodes easily compared to copper, Cu.
• Rusting of iron
Rusting is the common term for corrosion of iron, Fe. Rusting is the reaction of iron, Fe
and oxygen, O in the presence of water, H O or moisture. When iron, Fe corrodes, it
2
2
forms a red-brown hydrated metal oxide, (Fe O .xH O), commonly known as rust.
2 3 2
• Corrosion Corrosion of
Corrosion of copper, Cu occur to the materials made of copper or copper alloys. When metal chains
exposed to the atmosphere, copper oxidises, causing the bright copper surfaces to
tarnish. After a few years, this tarnish gradually changes to dark brown or black, and
finally to blue green. This oxide layer, is called patina, CuCO .Cu(OH) firmly adheres to
2
3
the outer surface of the copper and protects the underlying copper layers from further
corrosion. This is the reason why copper, Cu is used on roofs, gutter work and outdoor
sculptures. Corrosion of copper, Cu occurs at negligible rates in polluted air, water
and deaerated non-oxidising acids. However, it is susceptible to more rapid attack in
oxidising acids, oxidising heavy metal salts, sulphur, ammonia and some sulphur and Formation of
ammonia compounds. patina on outdoor
sculpture

344 1.6.1