Acids, Bases and Salts — Question 10

(a) Carbonic acid is a dibasic acid i.e., it has two replaceable hydrogen ions. Hence, it forms one acid salt or one normal salt. On the other hand, hydrochloric acid is a monobasic acid with one replaceable hydrogen ion. Hence, it forms only one normal salt.

(b) Concentration of an acid means the amount of water present in the acid and not at all the strength of an acid. Strength of an acid is the measure of concentration of hydronium ions it produces in its aqueous solution. Thus, dil. HCl is stronger acid than highly concentrated acetic acid.

(c) H₃PO₃ is not a tribasic acid but dibasic because in oxyacids of phosphorus, hydrogen atoms which are attached to oxygen atoms are replaceable. Hydrogen atoms directly bonded to phosphorus atoms are not replaceable.

(d) Generally, acids liberate carbon dioxide on reaction with metallic carbonates and bicarbonates. But if the salt produced is insoluble, then the reaction does not proceed. So, we do not expect lead carbonate to react with hydrochloric acid.

(e) Nitrogen dioxide is called double acid anhydride because two acids – nitrous acid and nitric acid – are formed when it reacts with water.

    2NO₂ + H₂O ⟶ HNO₂ + HNO₃