Concentration of Solutions
Percent by Mass
Problem 2. A medical solution used in a hospital is 0.9% by mass of NaCl. How many grams of NaCl are present in 100 g of the solution?
Answer
1. Known: % NaCl (m/m) = 0.9; mass of solution = 100.0 g
2. Unknown: mass of NaCl
3. Process: Use the equation:
\[
\begin{aligned}
\text{mass of NaCl}
&=
\left(
\frac{
0.9\,\%\,\text{NaCl} \times \text{mass of solution}
}{
100\,\%
}
\right)
\end{aligned}
\]
Therefore:
\[
\begin{aligned}
\text{mass of NaCl}
&=
\frac{
0.9\,\%\,\text{NaCl} \times 100\,\text{g}
}{
100\,\%
}
\end{aligned}
\]
4. Answer: There is 0.9 g NaCl in a 0.9% NaCl by mass in 100 g of medical solution.
