Page 145 - Chemistry_Form_2

Chemistry
for Secondary Schools

calcium chloride to absorb water vapour explains its use as a drying agent for
many gases, except ammonia gas because it reacts with it. The water absorbed
by the salt may result in changes in the physical properties, such as boiling point
and viscosity.
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Efflorescent salts
An efflorescent salt is the one which when left in air loses all the water of
crystallisation. Examples of efflorescent salts are hydrated sodium carbonate
(Na CO 10H O), hydrated sodium sulfate (Na SO 10H O), and hydrated iron(II)
●
●
2 3 2 2 4 2
sulfate (FeSO 7H O).
●
4 2
Uses of salts
Salts have many uses in our daily lives. Some common uses include controlling
soil pH, acting as antacids, serving as fertilisers, and helping to alleviate certain
health disorders. They are also used for flavouring and preservating food, as well
as in the production of pesticides.

Control of soil pH: Soils that are excessively acidic or alkaline are unsuitable for
crop production. Calcium oxide (lime) is usually added to acidic soils to neutralise
their acidity. When the soil is too alkaline, elemental sulfur or acidifying fertilisers
like ammonium sulfate (SA) are added to remedy the condition.

Uses of salts as antacids: Antacids are substances that are in the forms of
hydroxides or salts. These are used to relieve heartburn and acid build-up in the
stomach. Some of the common antacids are magnesium sulfate (Epsom salt),
aluminium hydroxide, and sodium hydrogencarbonate.

As inorganic fertilisers: Inorganic fertilisers are salts. Examples of these are
ammonium sulfate, ammonium nitrate, and calcium phosphate.

Alleviation of health disorders: Various salts are used to alleviate problems that
are associated with different health conditions. These salts include chlorides,
phosphates, and sulfates of sodium, potassium, and calcium.

Production of pesticides: Certain salts are used as pesticides to kill or control
pests such as insects, rodents, weeds and fungi. For example, copper(II) sulfate,
iron(II) sulfate, and sodium chlorate(V) are used as pesticides for controlling
fungi in crops.

Other uses of salts: There are many uses that are specific to some salts as
summarised in Table 5.13.

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