Hydrogen sulfide ( H₂S ) is a weak diprotic acid that ionizes in two successive steps in an aqueous solution, with ionization constants K_ a₁ and K_ a₂ . If K_ eq represents the overall ionization constant for the complete dissociation of H₂S into S²⁻ ions, which of the following statements are correct? A. pK_ eq = pK_ a₁ + pK_ a₂ B. pK_ a₁ > pK_ a₂ C. H₂S is a stronger acid than HS^- D. K_ eq = K_ a₁ K_ a₂ Choose th

Step-by-step solution

The ionization steps of H₂S are: H₂S H^+ + HS^- with ionization constant K_ a₁ HS^- H^+ + S²⁻ with ionization constant K_ a₂ The overall reaction is: H₂S 2H^+ + S²⁻ with overall ionization constant K_ eq From the equations, K_ eq = K_ a₁ K_ a₂ . Taking the negative logarithm on both sides: - K_ eq = - K_ a₁ - K_ a₂ pK_ eq = pK_ a₁ + pK_ a₂ Thus, statement A is correct and statement D is incorrect. For a polyprotic acid, the first ionization constant is always greater than the second because it is more difficult to