Question

Ethanol is $CH_3^{}C{H_2}OH$. Which species is formed when ethanol acts as a bronsted base?
A. $CH_3^{}C{H_2}O$
B. $C{H_3}C{H_2}^ + $
C. $C{H_3}C{H_2}O{H_2}^ + $
D. ${H_3}{O^ + }$

Answer 1

Hint: The Bronsted-Lowry theory is an acid base reaction theory proposed in 1923. The concept of this theory is that when an acid and base reacts with each other, the acid forms its conjugate base, and the base will form its conjugate acid.

Complete answer:
1. Arrhenius theory: This states that acid produces hydrogen cations when dissolved in water for example hydrochloric acid. Bases produce hydroxide ions when dissolved in water, for example sodium hydroxide. But this theory is only applicable in the aqueous solution.
2. Bronsted- Lowry theory: It was a broader definition than Arrhenius. According to them, acid is hydrogen – ion donor, and by donating a hydrogen ion its conjugate base will form. Similarly base is hydrogen- ion acceptor, and will form its conjugate acid.
Acid +base $ \rightleftharpoons $ conjugate base + conjugate acid
With an acid , HA, the equation can be written as
$HA + B \rightleftharpoons {A^ - } + H{B^ + }$
The equilibrium sign is used because the reaction can occur in both the direction, forward and backward.
In the question, we have ethanol, $CH_3^{}C{H_2}OH$ which when acted as bronsted base will form which species. So bronsted base will accept hydrogen ions and form a positive ion. So add a hydrogen to it and a positive charge.
Let’s react it with acid, HA, so we have the reaction as
$HA + C{H_3}C{H_2}OH \rightleftharpoons {A^ - } + C{H_3}C{H_2}O{H_2}^ + $

So the correct option will be C.

Note:
The 3rd theory was Lewis acid and base theory, which was based on electron pair donation and acceptance. According to this theory Lewis acids are electron pair acceptors. And Lewis bases are electron pair donors. That means here acids don’t even need hydrogen to show its acidic behavior.