Conjugate Acids & Bases (DP IB Chemistry)
Revision Note
Conjugate Acids & Bases
A Brønsted-Lowry acid is a species that can donate a proton
A Brønsted-Lowry base is a species that can accept a proton
In an equilibrium reaction, the products are formed at the same rate as the reactants are used
CH3COOH (aq) + H2O (l) ⇌ CH3COO- (aq) + H3O+ (aq)
acid base conjugate base conjugate acid
The reactant CH3COOH is linked to the product CH3COO- by the transfer of a proton from the acid to the base
Similarly, the H2O molecule is linked to H3O+ ion by the transfer of a proton
These pairs are therefore called conjugate acid-base pairs
A conjugate acid-base pair is two species that are different from each other by a H+ ion
Conjugate here means related
In other words, the acid and base are related to each other by one proton difference
Worked Example
In the equilibrium reaction shown below, which species are a conjugate acid-base pair?
CH3CH2CH2COOH (aq) + H2O (l) ⇌ CH3CH2CH2COO- (aq) + H3O+ (aq)
A. CH3CH2CH2COOH and H2O
B. H2O and H3O+
C. H2O and CH3CH2CH2COO-
D. CH3CH2CH2COO- and H3O+
Answer:
The correct option in B
A conjugate acid-base pair differ only by an H+ ion
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