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JEE MainChemistryIonic Equilibrium

Consider the following ionization reactions for hydrogen sulfide ( H₂S ) and their corresponding negative logarithmic equilibrium constants ( pK values): (i) H₂S H^+ + HS^- ; pK₁ (ii) HS^- H^+ + S²⁻ ; pK₂ (iii) H₂S 2H^+ + S²⁻ ; pK The correct relationship between pK , pK₁ , and pK₂ is:

Options

  1. ApK = pK₁ + pK₂
  2. BpK = pK₁ pK₂
  3. CpK = pK₁ - pK₂
  4. DpK = pK₁ pK₂

Correct answer

A. pK = pK₁ + pK₂

Step-by-step solution

The overall dissociation reaction (iii) is obtained by adding the stepwise dissociation reactions (i) and (ii). When chemical equations are added, their equilibrium constants are multiplied. Therefore, the equilibrium constant K for reaction (iii) is given by: K = K₁ K₂ Taking the negative base-10 logarithm on both sides, we get: - K = - (K₁ K₂) Using the properties of logarithms, this expands to: - K = - K₁ - K₂ Since pK = - K , substituting the respective pK values yields: pK = pK₁ + pK₂ Answer: pK = pK₁ + pK₂

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