Which of the following is not a conjugate acid-base pair?
A) NH4+/NH3 B) H30-OH OC) H2SO3/HSO3 D) C2H302-/HC2H302
The Correct Answer and Explanation is:
The correct answer is: B) H3O+/OH-
Explanation
In acid-base chemistry, a conjugate acid-base pair consists of two species that differ by one proton (H+). When an acid donates a proton, it forms its conjugate base, and when a base accepts a proton, it forms its conjugate acid. The pairs share this proton-exchange relationship.
Let’s analyze each option:
- A) NH4+/NH3
In this pair, NH4+ (ammonium) is the conjugate acid, and NH3 (ammonia) is the conjugate base. NH4+ can donate a proton to become NH3, making them a classic conjugate acid-base pair. - B) H3O+/OH-
H3O+ (hydronium) and OH- (hydroxide) do not form a conjugate acid-base pair. While both are common species in acid-base reactions, they do not differ by a single proton. Instead, H3O+ is the conjugate acid of water (H2O), and OH- is the conjugate base of water. In the reaction of water dissociating into H3O+ and OH-, they are not directly related as a conjugate pair; rather, they form as a result of water’s self-ionization. - C) H2SO3/HSO3-
In this case, H2SO3 (sulfurous acid) is the conjugate acid, and HSO3- (hydrogen sulfite) is the conjugate base. H2SO3 can lose a proton to become HSO3-, making them a proper conjugate acid-base pair. - D) C2H3O2-/HC2H3O2
This pair consists of acetate (C2H3O2-) as the conjugate base and acetic acid (HC2H3O2) as the conjugate acid. Acetic acid can donate a proton to become acetate, making them a correct conjugate acid-base pair.
In summary, H3O+ and OH- do not constitute a conjugate acid-base pair because they are not directly related by the loss or gain of a single proton; they exist as separate ions in the dissociation of water. Thus, option B is the correct answer, as it is the only choice that does not represent a conjugate acid-base relationship.