Which is the stronger Bronsted acid? Explain.

Question

Which is the stronger Bronsted acid? Explain.

a) HBrO or HBr

b) HNO or HNO₂

Answer 1

A Bronstead acid is one that can donate a proton (H+).

(a). HBr is stronger than HBrO because in HBr there is an H-Br bond and in HBrO there is an O-H bond. The O-H bond is stronger than the H-Br bond, so in HBr it is easier for the H⁺ to be liberated. We might better write the HBrO as BrOH since it really is an O-H bond.

(b). HNO₂ is a stronger acid because it has an additional oxygen and since oxygen is electronegative, it makes it easier for the H⁺ to be donated. Also, higher oxidation state of N in HNO₂ predicts stronger acid, and finally, more stable conjugate base suggests stronger acid (NO₂^- more stable than NO^-).