Page 32 - Curriculum Visions Dynamic Book

Sodium hydroxide
Sodium hydroxide, commonly known as caustic soda, is used in a wide range of chemical processes, from soap-making (see page 34),
to manufacturing dyes and cosmetics, paper and petrol. It can also be used as an environmentally friendly agent because it is able to remove sulphur-containing gases that might otherwise form acid rain.
Sodium hydroxide solution is colourless and reacts with many metal compounds or acids.
The action of sodium hydroxide on aluminium
is quite remarkable, as shown below, which suggests that you don’t clean aluminium pans with caustic soda.
Sodium hydroxide is made from brine by passing an electric current through it as shown
on page 26. Alternatively it can be made by reacting calcium hydroxide with sodium carbonate (the product of the Solvay process, page 28).
 The demonstration below shows how sodium hydroxide corrodes aluminium.
Properties of sodium hydroxide
Sodium hydroxide is a base, and as such it will produce an alkaline reaction when tested with a chemical indicator.
Sodium hydroxide is one of the few bases that are soluble in water. This makes it a very useful chemical. However, sodium hydroxide is a caustic material and will burn the skin and corrode some metals.
 The small aluminium container used in the demonstration.
 Sodium hydroxide is poured in and a reaction immediately begins.
EQUATION: Dissolving aluminium in sodium hydroxide
 Within a few minutes the base of the container has reacted and dissolved.
Aluminium + sodium hydroxide + water ➪ sodium aluminate + hydrogen 2Al(s) + 2NaOH(aq) + 6H2O(l) ➪ 2NaAl(OH)4(aq) + 3H2(g)
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