8. Acids, Bases and Salts (41.1 MB)

Acids, Bases and Salts
[H + ] > [OH – ]
and [H + ] > 1.0 × 10 –7 mol L –1
In other words the acidic solution is the one in which the concentration of H + (aq)
is greater than that of OH – (aq) ions.
We have seen earlier that the ionic product of water Kw is constant at a given
temperature. It can remain so only if the concentration of OH – (aq) ions decreases.
[OH – ] < 10 –7 mol L –1
(iii) Basic solutions
Bases furnish OH – (aq) ions in their solutions. This results in an increase in their
concentration. Therefore, in basic solution
[OH – ] > [H + ]
and [OH – ] > 1.0 × 10 –7 mol L –1
In other words, the basic solution is the one in which the concentration of H + (aq)
ions is smaller than that of OH –1 (aq) ions.
Here also, because of constancy of ionic product of water Kw, the concentration
of H + (aq) decreases. Thus
and [H + ] < 1.0 × 10 –7 mol L –1
We may summarize the nature of aqueous solution in terms of concentration of
hydrogen ions H + (aq) as shown in table 8.3.
Table 8.3 Concentration of H + (aq) ions in different
types of aqueous solutions
Nature of solution
Concentration of H + ions
at 25°C (298 K)
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Matter in our Surroundings
Notes
Neutral [H + ] = 1.0 × 10 –7 mol L –1
Acidic [H + ] > 1.0 × 10 –7 mol L –1
Basic [H + ] < 1.0 × 10 –7 mol L –1
INTEXT QUESTIONS 8.3
1. Why does the colour of dry blue litmus paper remains unchanged even when
it is brought in contact with HCl gas?
2. How does water help in dissociation of acids and bases?
3. Identify the nature of the following aqueous solutions (whether acidic, basic or
neutral)
(a) Solution A: [H + ] < [OH – ]
(b) Solution B: [H + ] > [OH – ]
(c) Solution C: [H + ] = [OH – ]
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