Define conjugate acid-base pair
A great advancement was made in the area of the conjugate acid-base pair when Bronsted and Lowry proposed in 1923 a new concept that is independent of solvents.
According to them, an acid is defined as any hydrogen-containing material (a molecule or a cation or an anion) that can release a proton (H⁺) to any other substance.
Whereas a base is a substance (a molecule or a cation or an anion) that can accept a proton from any other substance.
In short, an acid is a proton donor and a base is a proton acceptor.
A neutralization process has therefore involved a release of a proton by acid and the acceptance of proton by the base.
Neutral compounds or even ions could be designated as acids or bases according to this concept.
Examples of Bronsted acids
Examples of Bronsted Bases
What is conjugate acid-base pair with example?
When an acid release a proton (H+), the residue must be a base and this base can take up a proton (H+) to form original acid.
Thus acid-base neutralization involved two acid or two bases forming conjugated acid-base pairs.
Hence a conjugate base of an acid is that part left after the proton lost. Similarly, the conjugate acid of the base is the species formed on the addition of a proton to the base.
In the above reaction, HCl donates a proton to H2O, which is an acid. But H2O accepts a proton from HCl, which is a base.
In the reverse reaction which at equilibrium proceeds at the same rate as the forward reaction
H3O+ + Cl– → HCl + H2O
H3O+ ion donates a proton to Cl– ion, hence H3O+ ion is an acid. Cl– ion accepts a proton from H3O+ ion is a base.
Acid and conjugate base examples
The members of which can be formed from each other mutually by the gain or loss of protons are called conjugate acid-base pairs.
Thus a conjugate base of an acid is the part left after the proton (H+) lost. Similarly, the conjugate acid of a base is the species formed on the addition of a proton to a base.
|Conjugate Acid||Conjugate Base|
H+ + ClO4–
H+ + HSO4–
H+ + Cl–
H+ + NO3–
H+ + H2O
Conjugate acid-base pair reactions
An acid exhibits its acid properties only when it is allowed to react with a base. Similarly, a base displays its basic properties only when it exposed to an acid.
How do you identify acids and bases from an equation?
Conjugate acid of a species is the one that is obtained on the addition of a proton and the conjugate base of a species is one that is obtained on the release of a proton.
In the above reaction, HX– acts as a base and its conjugate acid is H2X.
In this reaction HX– acts as an acid thus its conjugated base is X-2.
In the same way, the conjugate acid of X-2 is HX– but X-2 cannot have any conjugated base because there is no proton that can release.
Conjugate base stability and acid strength
These hydrides become increasingly acidic order
Methane has negligible acidic properties, but ammonia donates a proton more to the strong base to form NH2–, water loses a proton even more readily and hydrogen fluoride is a fairly strong acid.
The increase in the acidic properties of these hydrides is due to the fact that as we move from CH4 to HF, the stability of their conjugate bases increases in the order,