# Question #745c2

Mar 9, 2017

$1.0 \cdot {10}^{- 4} \text{g NaCl}$

#### Explanation:

The thing to remember about concentrations expressed in parts per million is that they are calculated by looking at the number of parts of solute present for every ${10}^{6}$ parts of solution.

In other words, you're looking for the number of grams of solute present in ${10}^{6}$ grams of solution. This value will get you the solution's concentration in parts per million.

A $\text{1 ppm}$ solution will thus contain $\text{1 g}$ of solute for every ${10}^{6}$ $\text{g}$ of solution. Similarly, a $\text{100.0 ppm}$ solution will contain $\text{100.0 g}$ of solute for every ${10}^{6}$ $\text{g}$ of solution.

Now, you know that your solution must have a concentration of $100.0$ ppm and that the mass of the solution is equal to $\text{1.0 g}$.

Your goal here will be to use the solution's parts per million concentration as a conversion factor to calculate the number of grams of sodium chloride, your solute, needed to make this solution.

$1.0 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{g solution"))) * overbrace("100.0 g NaCl"/(10^6color(red)(cancel(color(black)("g solution")))))^(color(blue)("= 100.0 ppm NaCl solution")) = color(darkgreen)(ul(color(black)(1.0 * 10^(-4)color(white)(.)"g NaCl}}}}$

The answer is rounded to two sig figs, the number of sig figs you have for the mass of the solution.