Question

Which is NOT a conjugate acid-base pair, respectively?

A. HCN : CN⁻
B. SO₄²⁻ : HSO₄⁻
C. H₂O : OH⁻
D. H₃O⁺ : H₂O

Answer 1

Option B, SO₄²⁻ : HSO₄⁻, is not a conjugate acid-base pair because HSO₄⁻ is the conjugate acid of SO₄²⁻, not the conjugate base.

Step-by-step explanation:

To determine which is not a conjugate acid-base pair, it's essential to understand that a conjugate acid-base pair consists of two species that differ by one proton (H+). A conjugate acid has one more proton than its conjugate base.

• A. HCN : CN⁻ is a conjugate acid-base pair. HCN (hydrogen cyanide) is the conjugate acid and CN⁻ (cyanide ion) is the conjugate base.
• B. SO42⁻ : HSO4⁻ is not a conjugate acid-base pair because HSO4⁻ has one more proton than SO42⁻. SO42⁻ is the conjugate base of HSO4⁻.
• C. H2O : OH⁻ is a conjugate acid-base pair. H2O (water) is the conjugate acid and OH⁻ (hydroxide ion) is the conjugate base.
• D. H3O+ : H2O is a conjugate acid-base pair. H3O+ (hydronium ion) is the conjugate acid and H2O (water) is the conjugate base.

Therefore, the option that is not a conjugate acid-base pair is B. SO42⁻ : HSO4⁻.