When $25 \mathrm{~g}$ of $\mathrm{Na}_2 \mathrm{SO}_4$ is dissolved in $10^3 \mathrm{~kg}$ of solution, its…
When $25 \mathrm{~g}$ of $\mathrm{Na}_2 \mathrm{SO}_4$ is dissolved in $10^3 \mathrm{~kg}$ of solution, its concentration will be
$2.5 \mathrm{ppm}$
$25 \mathrm{ppm}$
$250 \mathrm{ppm}$
$100 \mathrm{ppm}$
Solution
When a solute is present in very minute amounts (trace quantities), the concentration is expressed in ppm.
$\begin{aligned}
& \text { ppm of } A=\frac{\text { mass of component } A}{\text { total mass of solution }} \times 10^6 \\
& =\frac{0.025}{10^3} \times 10^6=25 \mathrm{ppm} \text {. } \\
&
\end{aligned}$