Question

Giving suitable reasons, arrange hydrogen halides in the increasing order of their acidic strength.

Answer 1

1. As we move down the group from fluorine to iodine, the bond strength between hydrogen and the halogen \[\ce{(H - X)}\] decreases. A weaker bond means easier release of H⁺ ions, increasing acidity.
2. The size of the halogen atom increases down the group, making the bond longer and weaker.
3. Lower energy is needed to break the \[\ce{H - X}\] bond for heavier halogens, so they release H⁺ ions more easily.
4. Although fluorine is the most electronegative, its strong \[\ce{H - F}\] bond makes HF the least acidic among hydrogen halides.

Hence, the acidic strength increases from HF to HI due to decreasing bond strength and increasing atomic size of halogens. The acid strength order is HF < HCl < HBr < HI.