Question

All of the following anions are considered basic except A) F-. B) CN-. C) PO43-. D) HPO42-. E) Cl-.

Apparently the answer is E) Cl- but I dont understand, if Cl- is not basic than why isn't F- not also basic? Even with the differences in electronegativity I don't understand.

Thanks for ypur help!

Answer 1

Ans :- Cl^- is not a base .

Explanation :- HF , HCN , HPO₄^2- and H₂PO₄^- are weak acids therefore their conjugate bases i.e F^- , CN^- , PO₄^3- and HPO₄^2- respectively must be strong bases .  Hence F^- , CN^- , PO₄^3- and HPO₄^2- are basic ions .

On the other hand HCl is a strong acid therefore its conjugate base i.e Cl^- must be a very weak base ( even it is a weaker base than H₂O) . Cl^- has very limited potential to act as a base in the presence of acid because it has very low value of K_b. the effect on pH is almost negligible when chloride ions are introduced into aqueous solution . Hence Cl^- is a non-base .