Page 34 - Curriculum Visions Dynamic Book

The reaction of acids with bases
The reaction of acids and bases is very common. For example when naturally acidic rainwater falls on to (basic) limestone (calcium carbonate), the products are a salt, water and carbon dioxide. We know this reaction
as weathering. It is the action that changes solid rocks to small particles and soluble substances that can readily be moved by running water.
Such reactions have created the landscape all around us. The same thing happens when acid rain falls on the land, although in this case, neutralising the acid may be at the expense of nutrients in the soil.
In many industrial processes, chemists react one substance with another to produce useful products. It is also important to use just the right amount of each reagent so that nothing is wasted. In some cases it is also vital that the product be neutral (shampoos and face creams for example).
EQUATION: Titration of hydrochloric acid and sodium hydroxide
Sodium hydroxide + hydrochloric acid ➪ sodium chloride + water
NaOH(aq) + HCl(aq) ➪ NaCl(aq) + Sodium ion
H2O(l)
The sodium hydroxide (the alkali) contributes sodium ions and hydroxide ions.
The hydrochloric acid solution (the acid) contributes chloride ions and hydrogen ions (the latter associated with water molecules).
The sodium and chloride ions remain in solution unless the water is evaporated, causing the salt
to crystallise from the solution. Chemists call ions that have not been involved in the chemical reaction “spectator ions”.
Meanwhile, water molecules
are formed by the “neutralisation” of H+(aq) and OH–(aq) ions.
Chloride ion
Sodium and chloride ions
Hydroxide ion
Hydrogen ion associated with water
Water molecules
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