Question

Which halogen hydra acid is the weakest in aqueous solution?

Answer 1

Compound Chemical formula Aqueous phase (acid)

hydrogen fluoride (fluorane) HF hydrofluoric acid

hydrogen chloride (chlorane) HCl

hydrochloric acid

hydrogen bromide (bromane) HBr

hydrobromic acid

hydrogen iodide (iodane) HI hydroiodic acid

.

Answer 2

Answer:

HF is the weakest halogen hydra acid in aqueous solution.

Explanation:

• The halogen halides are soluble in water and their aqueous solution are acidic. The relative acidic strength of hydra acid increases down the group:

         HF < HCl < HBr < HI

• This order is exactly inverse that we expected on the basis of electronegativity. Because F is most electronegative so HF should have more ionic character and readily loss the H⁺ ion.
• In the aqueous solution:

          HX  ⇄   H⁺    +  X⁻

• The conjugate bases of HF, HCl, HBr and HI are F⁻, Cl⁻, Br⁻, I⁻ respectively. As we move down the group the size increases, the electron density from F⁻ to I⁻ decreases. With less electron density the tendency to attract the proton also decreases. Therefore basic character decrease down the group.
• Therefore F⁻ is strongest conjugate base of weakest acid HF.