JEE Main2013ChemistryIonic EquilibriumActual
Which one of the following arrangements represents the correct order of the proton affinity of the given species :
Options
- AI ⁻ < F ⁻ < HS ⁻ < NH ₂⁻
- BHS ⁻ < NH ₂⁻ < F ⁻ < I ⁻
- CF ⁻ < I ⁻ < NH ₂⁻ < HS ⁻
- DNH ₂⁻ < HS ⁻ < I ⁻ < F ⁻
Correct answer
A. I ⁻ < F ⁻ < HS ⁻ < NH ₂⁻
Step-by-step solution
The species with the greatest proton affinity will be the strongest base, and its conjugate acid will be the weakest acid. The weakest acid will have the smallest value of K _a . Since HI is a stronger acid than HF which is a stronger acid than H ₂ S , a partial order of proton affinity is I ⁻ < F ⁻ < HS ⁻ Since NH ₃ is a very weak acid, NH ₂⁻ must be a very strong base. Therefore the correct order of proton affinity is I ⁻ < F ⁻ < HS ⁻ < NH ₂⁻