Chemistry, Third edition

92 6 · REACTIONS OF IONS IN SOLUTION

2. Reaction with bases (neutralization)

Acids neutralize bases, producing a salt and water only. Examples of reactions of

alkalis with acids include

NaOH(aq)HCl(aq)NaCl(aq)H 2 O(l)

2KOH(aq)H 2 SO 4 (aq)K 2 SO 4 (aq)2H 2 O(l)

Both neutralization reactions reduce to the ionic equation

H 3 O+(aq) + OH(aq)2H 2 O(l)

or, more simply, as

H(aq)OH(aq)H 2 O(l)

Two examples of the reactions of insoluble bases with acids are

CuO(s)H 2 SO 4 CuSO 4 (aq)H 2 O(l)

MgO(s)2HNO 3 (aq)Mg(NO 3 ) 2 (aq)H 2 O(l)

Both reactions reduce to the ionic equation

O^2 (s)2H(aq)H 2 O(l)

where O^2 (s) is the oxide ion in the solid state.

A dramatic example of the reaction between H 2
and O 2. The airship Hindenbergcontained
200 000 m^3 of hydrogen in gas bags. A mixture
of air (oxygen) and hydrogen is extremely
flammable, and a stray spark caused the
Hindenbergto explode as it was landing in the
USA in 1937. The gas helium is also less dense
than air, and since it does not burn is much
safer to use in airships than hydrogen. However,
helium is very much more expensive.