Chapter 15, Problem 42A

Interpretation Introduction

Interpretation: Reason as to why the equivalent weight of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is half its molar mass is to be explained. Also the number of hydrogen ions that each ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ produces when reacting with an excess of ${\text{OH}}^{-}$ ions is to be given.

Concept introduction: Equivalent weight of an acid is the weight of the acid that is required to furnish one mol of hydrogen ions and molar mass of an acid is the mass of one mol of the acid.

Answer to Problem 42A

One mol of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ yields 2 moles of hydrogen ions. Accordingly, equivalent weight of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is half its molar mass. The number of hydrogen ions that each ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ produces when reacting with an excess of ${\text{OH}}^{-}$ ions is 2.

Explanation of Solution

Equivalent weight of an acid is the weight of the acid that is required to furnish one mol of hydrogen ions and molar mass of an acid is the mass of one mol of the acid.

One mol of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ yields hydrogen ions = 2 mol

One equivalent weight of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ yields hydrogen ions = 1 mol

So, two equivalent weight of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ yields hydrogen ions = 2 mol

Two equivalent weight of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ = Molar mass of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$

Thus, equivalent weight of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$

  $=\frac{1}{2}\text{Molar mass of acid}$

Also, each ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ molecule consists of 2 hydrogen atoms. So, number of hydrogen ions that each ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ produces when reacting with an excess of ${\text{OH}}^{-}$ ions is 2.

Conclusion

One mol of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ yields 2 moles of hydrogen ions. Accordingly, equivalent weight of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is half its molar mass. The number of hydrogen ions that each ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ produces when reacting with an excess of ${\text{OH}}^{-}$ ions is 2.