Question

Why is hydroiodic acid a strong acid?

Answer 1

Acid:

• A substance that furnishes ${\mathrm{H}}_3{\mathrm{O}}^{+}$ions in an aqueous solution is an acid.

Based on strength acids are of two types:

• A Strong acid (An acid that dissociates completely in an aqueous solution).
• A Weak acid (An acid that does not dissociate completely in an aqueous solution).

Strong acid:

• An acid that completely dissociates in an aqueous solution is a strong acid.
• For example: Hydrochloric acid $\left(\mathrm{HCl}\right)$, Sulphuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$.
• Here, the given acid is Hydroiodic acid $\left(\mathrm{HI}\right)$is a strong acid because it completely dissociates in water.
• Iodine is larger in size, whereas hydrogen is of small size. Due to this, the overlapping of the electron cloud is also not very proper.
• Due to this reason the bond energy between hydrogen and Iodine is very low. When treated with water they tend to ionize quickly.

Therefore, Hydroiodic acid is a strong acid because it gives ${\mathrm{H}}_3{\mathrm{O}}^{+}$ ions easily in an aqueous solution, and also it completely dissociates in water.

$\mathrm{HI}\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_3{\mathrm{O}}^{+}\left(\mathrm{aq}\right)+{\mathrm{I}}^{-}\left(\mathrm{aq}\right)$