Explain in detail whole bronsted lowry acid base theory
Answers
Definition of Brønsted-Lowry acids and bases, strong and weak acids and bases, and how to identify conjugate acid-base pairs.
Key points
A Brønsted-Lowry acid is any species that is capable of donating a proton—\text{H}^+H
+
.
A Brønsted-Lowry base is any species that is capable of accepting a proton, which requires a lone pair of electrons to bond to the \text{H}^+H
+
.
Water is amphoteric, which means it can act as both a Brønsted-Lowry acid and a Brønsted-Lowry base.
Strong acids and bases ionize completely in aqueous solution, while weak acids and bases ionize only partially.
The conjugate base of a Brønsted-Lowry acid is the species formed after an acid donates a proton. The conjugate acid of a Brønsted-Lowry base is the species formed after a base accepts a proton.
The two species in a conjugate acid-base pair have the same molecular formula except the acid has an extra \text H^+H
+
compared to the conjugate base.The Brønsted-Lowry theory describes acid-base interactions in terms of proton transfer between chemical species. A Brønsted-Lowry acid is any species that can donate a proton, \text{H}^+H
+
, and a base is any species that can accept a proton. In terms of chemical structure, this means that any Brønsted-Lowry acid must contain a hydrogen that can dissociate as \text H^+H
+
. In order to accept a proton, a Brønsted-Lowry base must have at least one lone pair of electrons to form a new bond with a proton.
Using the Brønsted-Lowry definition, an acid-base reaction is any reaction in which a proton is transferred from an acid to a base. We can use the Brønsted-Lowry definitions to discuss acid-base reactions in any solvent, as well as those that occur in the gas phase. For example, consider the reaction of ammonia gas, \text{NH}_3(g)NH
3
(g), with hydrogen chloride gas, \text{H}\text{Cl}(g)HCl(g), to form solid ammonium chloride, \text{NH}_4 \text{Cl}(s)NH
4
Cl(s):
\text{NH}_3(g)+\blueD{\text{H}}\text{Cl}(g)\rightarrow\text{N}\blueD{\text{H}}_4\text{Cl}(s)NH
3
(g)+HCl(g)→NH
4
Cl(s)
This reaction can also be represented using the Lewis structures of the reactants and products, as seen below:
Lewis structure of ammonia—a nitrogen with a lone pair of electrons that is also bound to 3 hydrogens—plus the Lewis structure of hydrochloric acid forms ammonium chloride.
Lewis structure of ammonia—a nitrogen with a lone pair of electrons that is also bound to 3 hydrogens—plus the Lewis structure of hydrochloric acid forms ammonium chloride.
In this reaction, \blueD{\text{H}}\text{Cl}HCl donates its proton—shown in blue—to \text{NH}_3NH
3
. Therefore, \text{HCl}HCl is acting as a Brønsted-Lowry acid. Since \text{NH}_3NH
3
has a lone pair which it uses to accept a proton, \text{NH}_3NH
3
is a Brønsted-Lowry base.
Note that according to the Arrhenius theory, the above reaction would not be an acid-base reaction because neither species is forming \text{H}^+H
+
or \text{OH}^-OH
−
in water. However, the chemistry involved-−a proton transfer from \text{HCl}HCl to \text{NH}_3NH
3
to form \text{NH}_4 \text{Cl}NH
4
Cl-−is very similar to what would occur in the aqueous phase.
To get more familiar with these definitions, let's examine some more examples.
Identifying Brønsted-Lowry acids and bases
In the reaction between nitric acid and water, nitric acid, \text{HNO}_3HNO
3
, donates a proton—shown in blue—to water, thereby acting as a Brønsted-Lowry acid.
\blueD{\text{H}}\text{NO}_3(aq)+\text{H}_2\text{O}(l)\rightarrow\blueD{\text{H}}_3\text{O}^+(aq)+\text{NO}_3^-(aq)HNO
3
(aq)+H
2
O(l)→H
3
O
+
(aq)+NO
3
−
(aq)
Since water accepts the proton from nitric acid to form \blueD{\text{H}}_3\text{O}^+H
3
O
+
, water acts as a Brønsted-Lowry base. This reaction highly favors the formation of products, so the reaction arrow is drawn only to the right.
Let's now look at a reaction involving ammonia, \text{NH}_3NH
3
, in water:
\text{NH}_3(aq)+\blueD{\text{H}}_2\text{O}(l)\rightleftharpoons\text{N}\blueD{\text{H}}_4^+(aq)+\text{OH}^-(aq)NH
3
(aq)+H
2
O(l)⇌NH
4
+
(aq)+OH
−
(aq)
In this reaction, water is donating one of its protons to ammonia. After losing a proton, water becomes hydroxide, \text{OH}^-OH
−
. Since water is a proton donor in this reaction, it is acting as a Brønsted-Lowry acid. Ammonia accepts a proton from water to form an ammonium ion, \text{NH}_4^+NH
4
+
. Therefore, ammonia is acting as a Brønsted-Lowry base.
Bronsted-Lowry Theory of acids and bases. The theory. An acid is a proton (hydrogen ion) donor. A base is a proton (hydrogen ion) acceptor.