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Like magnesium oxide, iron oxide will also behave basic in nature when
dissolved in water.
Copper also gets corroded due to exposure to moist air. It develops a coating
of green colour on it. The green coating is a mixture of copper hydroxide
Cu(OH) 2 and copper carbonate CuCO 3. The green coating is also known as
‘Patina’.
The equation can be written as.
2Cu + H 2O + CO 2 + O 2 Cu (OH) 2 + CuCO 3
(Copper) [Moist air ] (Copper hydroxide) (Copper carbonate)

 You might have observed silver ornaments turning black in colour after
some time. It is known as the silver has tarnished. This process is
called tarnishing of silver. It happens when silver is exposed to air
containing Sulphur gas, it discolours and then darkens as it reacts with
the gas to form a surface layer of tarnish.
The equation can be given as
2Ag + H 2S Ag 2S + H 2
Silver Hydrogen sulphide Silver sulphide Hydrogen
Note: - Silver is one of the noble metals, it doesn’t react easily.
 Gold being the least reactive doesn’t react easily.
 Metal Oxides like Aluminium oxide (Al 2O 3) and Zinc oxide (ZnO) show both
the acidic as well as basic oxide. These kind of oxides are known as
amphoteric oxide. You will study in detail in higher class.

Reaction of non-metals with oxygen.When non-metals react with oxygen,
respective non-metallic oxides are formed which is acidic in nature.

E.g. when powdered Sulphur is burnt in presence of air, Sulphur dioxide is formed.
When this gas (Sulphur dioxide) is passed through water it forms sulphurous acid
which turns blue litmus red showing that non-metallic oxide are acidic in nature.

S + O 2 SO 2

Sulphur Oxygen Sulphur dioxide

SO 2 + H 2O H 2SO 3

Sulphur dioxide Water Sulphurous acid.

Similarly, when coal (carbon) is brunt in air, it releases carbon dioxide gas. When
this gas is mixed with water it produces carbonic acid, which turns blue litmus red.

C + O 2 SO 2

Coal/ carbon Oxygen Carbon dioxide

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