Chemistry, Third edition

REACTIONS OF ACIDS

Bases and alkalis

A base is a substance that reacts with an acid in solution producing a salt and

water only.

Generalizing:

acidbasesaltwater

This reaction is known as neutralization.

An alkali is a base that dissolves in water(Fig. 6.5). A solution of an alkali

contains the hydroxide ion, OH(aq).

Alkalis are usually hydroxides of metals. The common alkalis are the hydroxides

of calcium, potassium and sodium. They are all are ionic solids which completely

dissociate into ions in water, for instance:

H 2 O

Na,OH(s)Na(aq)OH(aq)

sodium hydroxide hydroxide

ion

Ammonia solution is also regarded as an alkali because it contains the hydroxide ion.

Bases which are insoluble in water include the oxides of metals such as mag-

nesium oxide (Mg^2 ,O^2 ) and copper(II) oxide (Cu^2 ,O^2 ) and organic com-

pounds (compounds based on carbon) which contain nitrogen atoms such as

propylamine (C 3 H 7 NH 2 ).

91

Number of acidic hydrogen atoms

1.How many acidic hydrogen atoms do molecules of (i)sulfuric acid and (ii)hydrogen chloride

possess?

2.Hydrochloric acid forms salts known as chlorides. What are names of the types of salts

produced from (i)ethanoic acid and (ii)nitric acid?

Exercise 6I

Alkalis

Bases

Fig. 6.5Bases and alkalis –

although all alkalis are bases,

not all bases are alkalis.

Reactions of acids

The reactions of acids are the reactions of the H(aq) ion).

1. Effect on acid–base indicators

Taking litmus as our example:

OH(aq)

red coloured litmus \=====\blue coloured litmus

H(aq)

6.5

Dissolution of potassium and calcium hydroxides

Write an equation showing the dissolution of potassium and calcium hydroxides in water.

Exercise 6J