Chapter 10.4, Problem 55PP

Interpretation Introduction

Interpretation:

The largest percent by mass of sulphur needs to be determined.

${\text{H}}_{\text{2}}{\text{SO}}_{\text{3}}\left(\text{Sulphuric acid}\right)$ or ${\text{H}}_{\text{2}}{\text{S}}_2{\text{O}}_8\left(\text{Peroxydisulphuric acid}\right)$

Concept used: In stachiometry, a compound which is formed from atoms of elements, can be used to find out percentage by mass composition of that atom from the molecular formula of the compound.

$\text{Percent composition by mass = }\frac{\text{Mass of atom}}{\text{Total mass of compound}}\times 100$

Answer to Problem 55PP

${\text{H}}_{\text{2}}{\text{SO}}_{\text{3}}$ has larger percent by mass of sulphur

Explanation of Solution

To find the percent by mass of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{3}}$ and ${\text{H}}_{\text{2}}{\text{S}}_2{\text{O}}_8$

Atomic mass of Hydrogen $\text{=1 g}$

Atomic mass of Sulphur $\text{=32 g}$

Atomic mass of oxygen $\text{=16 g}$

$\text{Mass of atom in the compound}\Rightarrow \text{number of atoms in the compound}\times \text{molarmass of that compound}$ For ${\text{H}}_{\text{2}}{\text{SO}}_{\text{3}}$

Total molecular mass $\Rightarrow 2\times 1+32+3\times 16$

$\Rightarrow 82\text{ g}$

Percent composition of sulphur $=\frac{32}{82}\times 100=39\%\mathrm{.......}\text{ 1}$

For ${\text{H}}_{\text{2}}{\text{S}}_2{\text{O}}_8$

Total molecular mass $\Rightarrow 2\times 1+2\times 32+8\times 16\Rightarrow 194\text{ g}$

Percent composition of sulphur $=\frac{64}{194}\times 100$

$=32.9\%\mathrm{.......}\text{ 2}$

Comparing 1 and 2

${\text{H}}_{\text{2}}{\text{SO}}_{\text{3}}$ has more percentage by mass of sulphur than ${\text{H}}_{\text{2}}{\text{S}}_2{\text{O}}_8$.