Common Behaviour of Acids and Bases
In the following section, we will find the answers of following questions-
(i) All acids have similar chemical properties. All bases have similar chemical properties. What lead to this similarity in properties?
(ii) How acids and bases are different chemically?
Group A Group B
Hydrochloric acid (HCl) Sodium hydroxide ((NaOH))
Sulphuric acid (H2SO4) Calcium hydroxide [Ca(OH)2]
Nitric acid (HNO3) Potassium hydroxide (KOH)
Acetic acid (CH3COOH) Magnesium hydroxide [Mg(OH)2]
Formic acid (HCOOH) Ammonium hydroxide (NH4OH)
Carbonic acid (H2CO3)
Phosphoric acid (H3PO4)
Compounds of group ‘A’ behave similar on indicators and in properties, are denoted as acids. While, compounds of group ‘B’ show similarity on indicators and in properties, are called as bases. Group A and B behave opposite to each other.
All acids contain hydrogen atoms. When an acid is dissolved in water or react with metals, it liberates hydrogen ion(s) (H+) and negatively charged counterpart. For e.g. HCl gives H+ and Cl–.
HCl (aq) → H+ (aq) + Cl– (aq)
H2SO4 (aq) → 2H+ (aq) + SO4– 2 (aq)
HNO3 (aq) → H+ (aq) + NO3– (aq)
CH3COOH (aq) → H+ (aq) + CH3COO– (aq)
HCOOH (aq) → H+ (aq) + HCOO– (aq)
H2CO3 (aq) → H+ (aq) + HCO3– (aq)
H3PO4 (aq) → H+ (aq) + H2PO4– (aq)
It means, presence of H+ ion(s) and liberation of H+ ion when dissociates / ionizes in water from acids, give them acidic properties. It is also important to note that all compounds containing hydrogen are not acids.
Like acids, when a base is dissolved in water, it gives hydroxide ion(s) (OH –) and its positive counterpart.
NaOH (aq) → Na+ (aq) + OH– (aq)
Ca(OH)2 (aq) → Ca+ (aq) + 2OH– (aq)
KOH (aq) → K+ (aq) + OH– (aq)
Mg(OH)2 (aq) → Mg+ (aq) + 2OH– (aq)
NH4OH (aq) → NH4+ (aq) + OH– (aq)
Thus, liberation of OH– ions from a base when dissociates / ionizes in solution, give basic properties. Further, all compounds containing hydroxide group are not bases.
♦ NH3 does not contain hydroxyl group, even then it is considered as a base because when it is dissolved in water, it forms ammonium hydroxide (NH4OH) which ionizes to give OH– ions in the solution.
♦ The aqueous solutions of acids and bases conduct electricity.
♦ Acids produce H+ (aq) ion(s) in solution whereas bases produce OH– (aq) ion(s) in solution
♦ H+ ions are highly active. They combine immediately with polar water molecules and form hydronium ions (H3O+)
H+ + H2O → H3O+
Thus, hydrogen ions [H+ (aq)] can also be represented as hydronium ion (H3O+ ).
When an acid and a base are mixed, they neutralize each other’s effects. Such reactions are called neutralization reaction. This is the reason, an acid turns blue litmus into red and oppositely, a base turns red litmus into blue.
Acid + Base → Salt + Water
HA + BOH → HOH + BA
H+ (aq) + OH– (aq) → HOH(l)
Acidic / Basic behaviour in presence of water