Question

How would you compare the Arrhenius and Bronsted-Lowry models of acids and bases?

Answer 1

Hint: Arrhenius explained acid and bases as dissociation hydrogen ions and hydroxide ions in water respectively whereas Bronsted Lowry explained acids and bases by donation or acceptance of protons that are hydrogen ions respectively.

Complete step-by-step answer: Let us discuss Arrhenius and Bronsted-Lowry models of acids and bases.
-According to Arrhenius model, acids are the substances which dissociates in water to give ${{H}^{+}}_{(aq)}$ ions or increase the concentration of ${{H}^{+}}_{(aq)}$ions whereas bases are the substances which dissociates in water to give $O{{H}^{-}}_{(aq)}$ ions or increase the concentration of $O{{H}^{-}}_{(aq)}$ ions.
Ionization of Arrhenius acid in water is represented below:-
$H{{X}_{(aq)}}\xrightarrow{{}}{{H}^{+}}_{(aq)}+{{X}^{-}}_{(aq)}$
Since, bare proton is very reactive and cannot exist freely in aqueous solutions, therefore it bonds with solvent such as water to form hydronium ion (${{H}_{3}}{{O}^{+}}$).
$H{{X}_{(aq)}}+{{H}_{2}}{{O}_{(l)}}\xrightarrow{{}}{{H}_{3}}{{O}^{+}}_{(aq)}+{{X}^{-}}_{(aq)}$
Similarly, the ionization of Arrhenius base is represented below:-
$MO{{H}_{(aq)}}\xrightarrow{{}}{{M}^{+}}_{(aq)}+O{{H}^{-}}_{(aq)}$
-According to Bronsted-Lowry model, acids are the substances which are capable of donating hydrogen ions ${{H}^{+}}$whereas bases are the substances which are capable of accepting hydrogen ions ${{H}^{+}}$. In other words, acids can be said as proton donors and bases can be said as proton acceptors.
 $N{{H}_{3}}_{(aq)}+{{H}_{2}}{{O}_{(l)}}\xrightarrow{{}}N{{H}_{4}}{{^{+}}_{(aq)}}+O{{H}^{-}}_{(aq)}$
Here, we can observe that ammonia ($N{{H}_{3}}$ ) acts as Bronsted-Lowry base because it accepts ${{H}^{+}}$ion and water (${{H}_{2}}O$ ) as Bronsted-Lowry acid because it donates ${{H}^{+}}$ion.
$HC{{l}_{(aq)}}+{{H}_{2}}{{O}_{(l)}}\xrightarrow{{}}{{H}_{3}}{{O}^{+}}_{(aq)}+C{{l}^{-}}_{(aq)}$
Here, we can observe that water (${{H}_{2}}O$ ) acts as Bronsted-Lowry base because it accepts ${{H}^{+}}$ion and hydrochloric acid (HCl) as Bronsted-Lowry acid because it donates ${{H}^{+}}$ion.

Note:-The limitation of Arrhenius model was that it was only applicable to aqueous solution and it wasn’t able to explain the basic nature of those substances which do not have hydroxide ions like ammonia.
-It is interesting to see that water acts as a base with HCl and as a base with $N{{H}_{3}}$ which represents its amphoteric (substances which can be acid as well as base) nature.