Page 45 - Science Class 07

2Ca + O 2CaO Test for Bases
2
(Calcium (Oxygen) (Calcium oxide) v Bases turn red litmus-paper blue.
Metallic oxides are called basic oxides, as these v Methyl orange turns yellow.

can react with acids to form salts and water. v Phenolphthalein turns pink.
PREPARATION OF ALKALIES Uses of Bases

Alkalies can be prepared by dissolving metal Bases are extensively used by us in our daily
oxides in water. life. They are used as laboratory reagents and
For example: in industries. The most commonly used bases

CaO + H O Ca (OH) 2 are calcium hydroxide [Ca(OH) ], sodium
2
2
hydroxide (NaOH) and ammonium hydroxide
(Calcium (Water) (Calcium
oxide) hydroxide) (NH OH).
4
MgO + H O Mg(OH) Calcium Hydroxide
2 2
(Magnesium (Water) (Magnesium Calcium hydroxide is commonly known as
Oxide) hydroxide)
slaked lime.
Proper es of Alkalies
Its main uses are as follows:
v Alkalies are bi er in taste.
v As a subs tute for cement in low cost
v They are slippery in nature.
construc on.
v Strong alkalies are corrosive in nature. They
v For white washing of buildings.
produce painful blister if fall on our skin.
v To manufacture bleaching powder.

v For neutralizing acidity of soil : Soil
becomes acidic because of excessive use of
Prepara on of an aklali Mg (OH)
2 chemical fer lizers. Plants do not grow well
Take a strip of magnesium wire and hold it in acidic soil. Quicklime (calcium oxide) or
with a pair of tongs over a flame. It will start slaked lime (calcium hydroxide) is added to
burning. Collect the ash produced by it. It is soil to neutralize the acid present in it.
magnesium oxide. Dissolve it in a glass of
v For treatment of waste water : Wastes
water.
from many factories contain acids. If such
In a few minutes, the
magnesium oxide will water is released into a water body, it can
harm the fish and other water animals. The
completely dissolve in
water. The water will turn factory wastes are therefore treated with
in to a soapy solu on. Dip calcium hydroxide to neutralize the acid
a red litmus paper in the before the waste water is disposed off.
solu on. It will turn blue. Sodium Hydroxide
So, the solu on formed is Sodium hydroxide is commonly known as
an alkali magnesium
caus c soda. It is obtained commercially from
hydroxide.
concentrated brine (salt water).

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