Question

According to Arrhenius theory HCl gas is an acid - True or False?

• A. True
• B. False

Answer 1

The correct option is B

False

According to the Arrhenius theory of acids and bases:
Acids donate $H^{+}$ ions in solution while bases donate OH^- in solution. Neutralization is the reaction between $H^{+}$ and ${OH}^{-}$ ions to yield water.
This theory has some limitations.
$N{H}_3$ (aq) + HCl (aq) →$N{H}_{4}Cl$ (aq)
Note the reactants and the product in the above reaction. Arrhenius theory explains the acidic nature of HCl (aq). The same reaction happens in the gaseous phase to give the same product! But there are no H⁺ or OH^- ions. So this theory does not consider the following reaction as an acid-base reaction.
$N{H}_3$ (g) + HCl (g) →$N{H}_{4}Cl$ (s)
Arrhenius theory fails to explain the acidic nature of HCl gas
Bronsted Lowry theory:
This is a slight modification of Arrhenius theory. According to the Bronsted-Lowry theory of acids and bases,
An acid is a proton donor while a base is a proton acceptor.
Here, the reaction $N{H}_3$ (g) + HCl (g) →$N{H}_{4}Cl$ (s) is consistent with an acid-base explanation. In other words, HCl (g) is an acid. $N{H}_3$ (g) (or aq) is a base. For that matter, anything that accepts a proton H⁺ is a Bronsted-Lowry base.
The current definition of acids and bases is based on the Lewis acid-base theory, which states that:
Acids are electron-pair acceptors. Ex: $AlC{l}_3$ $B{F}_3$
Bases are electron-pair donors. Ex $N{H}_3$, $RN{H}_2$

Throughout ionic equilibrium, the Arrhenius definition is good enough. Though outdated, this theory is more than sufficient for this chapter.