Explain how to identify a conjugate acid and a conjugate base in an acid base reaction.
– Identify the acid and base in the reaction.
– What is left of the base after the reaction is known as the conjugate acid, while what is left of the acid after the reaction is known as the conjugate base.
Types of acids and bases:
When we are looking at conjugate acid and base, the type of acid and base we should focus on are Brønstead acid and base.
Brønsted acid: proton donor
Brønsted base: proton acceptor
Do note that proton here refers to hydrogen ion, H⁺.
Other types of acids and bases includes arrhenius acid/base and Lewis acid/base.
Conjugate acid is what remains of the acid when a Brønsted acid donates a proton, while conjugate base is the newly formed protonated species when a Brønsted base accepts a proton.
Let’s look at an example of a Brønsted acid-base reaction:
NH₃(aq) +H₂O(l) ⇌ NH₄⁺(aq) +OH⁻(aq)
Here, the base is NH₃ and the acid is H₂O.
NH₄⁺ is the conjugate acid, while OH⁻ is the conjugate base.
For a Brønsted acid- base reaction, whether a substance behaves as an acid or a base depends on what it is reacting with. Although H₂O behaves as an acid in this example, it behaves as a base when reacting with HCl.
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