Page 34 - NCERT Science Class 10 English Medium

n Identify the acids and bases from which the above salts may be
obtained.
n Salts having the same positive or negative radicals are said to
belong to a family. For example, NaCl and Na SO belong to the
2 4
family of sodium salts. Similarly, NaCl and KCl belong to the family
of chloride salts. How many families can you identify among the
salts given in this Activity?

2.4.2 pH of Salts

Activity 2.142.14
Activity 2.14
Activity 2.14
Activity 2.14
Activity
n Collect the following salt samples – sodium chloride, potassium
nitrate, aluminium chloride, zinc sulphate, copper sulphate,
sodium acetate, sodium carbonate and sodium hydrogencarbonate
(some other salts available can also be taken).
n Check their solubility in water (use distilled water only).
n Check the action of these solutions on litmus and find the pH
using a pH paper.
n Which of the salts are acidic, basic or neutral?
n Identify the acid or base used to form the salt.
n Report your observations in Table 2.4.

Salts of a strong acid and a strong base Table 2.4
are neutral with pH value of 7. On the other
hand, salts of a strong acid and weak base Salt pH Acid used Base used
are acidic with pH value less than 7 and those
of a strong base and weak acid are basic in
nature, with pH value more than 7.

2.4.3 Chemicals from Common Salt

By now you have learnt that the salt formed
by the combination of hydrochloric acid and
sodium hydroxide solution is called sodium
chloride. This is the salt that you use in food.
You must have observed in the above Activity
that it is a neutral salt.
Seawater contains many salts dissolved
in it. Sodium chloride is separated from these
salts. Deposits of solid salt are also found in
several parts of the world. These large crystals
are often brown due to impurities. This is
called rock salt. Beds of rock salt were formed
when seas of bygone ages dried up. Rock salt
is mined like coal.
You must have heard about Mahatma Gandhi’s Dandi March. Did
you know that sodium chloride was such an important symbol in our
struggle for freedom?

Acids, Bases and Salts 29

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