Page 35 - NCERT Science Class 10 English Medium

Common salt — A raw material for chemicals
The common salt thus obtained is an important raw material for various
materials of daily use, such as sodium hydroxide, baking soda, washing
soda, bleaching powder and many more. Let us see how one substance
is used for making all these different substances.

Sodium hydroxide
When electricity is passed through an aqueous solution of sodium
chloride (called brine), it decomposes to form sodium hydroxide. The
process is called the chlor-alkali process because of the products formed–
chlor for chlorine and alkali for sodium hydroxide.
2NaCl(aq) + 2H O(l) → 2NaOH(aq) + Cl (g) + H (g)
2 2 2
Chlorine gas is given off at the anode, and hydrogen gas at the cathode.
Sodium hydroxide solution is formed near the cathode. The three
products produced in this process are all useful. Figure 2.8 shows the
different uses of these products.

Figure 2.8
Figure 2.8
Figure 2.8
Figure 2.8 Important products from the chlor-alkali process
Figure 2.8
Bleaching powder
You have already come to know that chlorine is produced during the
electrolysis of aqueous sodium chloride (brine). This chlorine gas is used
for the manufacture of bleaching powder. Bleaching powder is produced
by the action of chlorine on dry slaked lime [Ca(OH) ]. Bleaching powder
2
is represented as CaOCl , though the actual composition is quite
2
complex.
Ca(OH) + Cl → CaOCl + H O
2 2 2 2

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