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Chemistry

Define the following as per ionic theory with examples and ionic equations wherever relevant :

(i) acid (ii) base (iii) alkali (iv) neutralization

Acids Bases Salts

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Answer

(i) Acid — An acid is a compound which when dissolved in water yields hydronium ions [H3O+] as the only positively charged ion.

HCl (aq) ⇌ H+ + Cl-

H+ + H2O ⇌ H3O+ [hydronium ion]

HCl + H2O ⇌ H3O+ + Cl-

(ii) Base — A base is a compound which reacts with hydronium ions of an acid to give salt and water only.

CuO + 2HCl ⟶ CuCl2 + H2O

Cu(OH)2 + H2SO4 ⟶ CuSO4 + 2H2O

  • Bases are oxides or hydroxides of a metal [including ammonium hydroxide]

  • Examples of insoluble bases [i.e., not alkalis] — ZnO, PbO, CuO, Fe(OH)2, Pb(OH)2, Cu(OH)2

(iii) Alkali — An alkali is a compound which when dissolved in water yields hydroxyl ions [OH-] as the only negatively charged ions.

NaOH [aq.] ⇌ Na+ + OH- [Hydroxyl or hydroxide ion]

Alkali is a base, soluble in water. [All alkalis are bases, but all bases are not alkalis.]

Examples of soluble bases [i.e., alkalis] — KOH, NaOH [strong alkalis] , Ca(OH)2, NH4OH (weak alkalis).

(iv) Neutralization — It is the process due to which [H+] ions of an acid react completely or combine with [OH-] ions of a base to give salt and water only.

Acid + Base ⟶ Salt + Water

HCl + NaOH ⟶ NaCl + H2O

H+Cl- + Na+OH- ⟶ Na+Cl- + H2O

[H+ (aq) + OH- (aq) ⇌ H2O (l)]

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