state Bronsted Lowery concept of acid and base prove with one example
Answers
Brønsted-Lowry theory of acid and bases took the Arrhenius definition one step further, as a substance no longer needed to be composed of hydrogen (H+) or hydroxide (OH-) ions in order to be classified as an acid or base. For exmapl, consider the following chemical equation:
\[ HCl \; (aq) + NH_3 \; (aq) \rightarrow NH_4^+ \; (aq) + Cl^- \; (aq) \]
Here, hydrochloric acid (HCl) "donates" a proton (H+) to ammonia (NH3) which "accepts" it , forming a positively charged ammonium ion (NH4+) and a negatively charged chloride ion (Cl-). Therefore, HCl is a Brønsted-Lowry acid (donates a proton) while the ammonia is a Brønsted-Lowry base (accepts a proton). Also, Cl- is called the conjugate base of the acid HCl and NH4+ is called the conjugate acid of the base NH3.
A Brønsted-Lowry acid is a proton (hydrogen ion) donor.
A Brønsted-Lowry base is a proton (hydrogen ion) acceptor.
In this theory, an acid is a substance that can release a proton (like in the Arrhenius theory) and a base is a substance that can accept a proton. A basic salt, such as Na+F-, generates OH- ions in water by taking protons from water itself (to make HF):
\[F^-_{(aq)} + H_2O_{(l)} \rightleftharpoons HF_{(aq)} + OH^-\]
When a Brønsted acid dissociates, it increases the concentration of hydrogen ions in the solution, \([H^+]\); conversely, Brønsted bases dissociate by taking a proton from the solvent (water) to generate \([OH^-]\).
Acid dissociation
\[HA_{(aq)} \rightleftharpoons A^-_{(aq)} + H^+_{(aq)}\]
Acid Ionization Constant:
\[K_a=\dfrac{[A^-][H^+]}{[HA]}\]
Base dissociation:
\[B_{(aq)} + H_2O_{(l)} \rightleftharpoons HB^+_{(aq)} + OH^-_{(aq)}\]
Base Ionization Constant
\[K_b = \dfrac{[HB^+][OH^-]}{[B]}\]
The determination of a substance as a Brønsted-Lowery acid or base can only be done by observing the reaction. In the case of the HOH it is a base in the first case and an acid in the second case.
To determine whether a substance is an acid or a base, count the hydrogens on each substance before and after the reaction. If the number of hydrogens has decreased that substance is the acid (donates hydrogen ions). If the number of hydrogens has increased that substance is the base (accepts hydrogen ions). These definitions are normally applied to the reactants on the left. If the reaction is viewed in reverse a new acid and base can be identified. The substances on the right side of the equation are called conjugate acid and conjugate base compared to those on the left. Also note that the original acid turns in the conjugate base after the reaction is over.
Answer:
In the Brønsted-Lowry definition of acids and bases, an acid is a proton (H⁺) donor, and a base is a proton acceptor. When a Brønsted-Lowry acid loses a proton, a conjugate base is formed. Similarly, when a Brønsted-Lowry base gains a proton, a conjugate acid is formed.
HCl(g) is the proton donor and therefore a Brønsted-Lowry acid, while H 2O is the proton acceptor and a Brønsted-Lowry base. These two examples show that H 2O can act as both a proton donor and a proton acceptor, depending on what other substance is in the chemical reaction.