Question

Which one is stronger $\mathrm{HCl}$ or ${\mathrm{H}}_2{\mathrm{SO}}_4$?

Answer 1

Stronger acid:

1. An acid is a substance that is able to donate the hydrogen ion to another substance.
2. $\mathrm{HCl}$ and ${\mathrm{H}}_2{\mathrm{SO}}_4$ both are strong acids when compared to other acids.
3. $\mathrm{HCl}$ dissolves in water and gives ${\mathrm{H}}^{+}$and ${\mathrm{Cl}}^{-}$ions. The ions are completed dissociated.
4. ${\mathrm{H}}_2{\mathrm{SO}}_4$dissolves in water and gives ${\mathrm{H}}_3{\mathrm{O}}^{+}$and ${\mathrm{HSO}}_4^{-}$. But the ions are partially dissociated.
5. $\mathrm{HCl}$ is stronger than ${\mathrm{H}}_2{\mathrm{SO}}_4$ because of the acid dissociation constants of the acids.
6. The smaller the ${\mathrm{pK}}_{\mathrm{a}}$, the stronger the acid.
7. The ${\mathrm{pK}}_{\mathrm{a}}$of $\mathrm{HCl}$ is $-6.3$. The ${\mathrm{pK}}_{\mathrm{a}}$of ${\mathrm{H}}_2{\mathrm{SO}}_4$ is $-3.0$.
8. Since the acid dissociation constant of $\mathrm{HCl}$ is low, it can dissociate very easily and it is more acidic.

Therefore, $\mathrm{HCl}$ is stronger than ${\mathrm{H}}_2{\mathrm{SO}}_4$.