# Question 97eda

Jul 27, 2017

$\text{2% NaCl}$

#### Explanation:

Your goal here is to figure out the number of grams of sodium chloride, your solute, present in $\text{100 g}$ of this solution.

Since you know that your sample contains $\text{0.5 g}$ of sodium chloride in $\text{20 g}$ of water, you can say that the mass of the solution is equal to

overbrace("0.5 g")^(color(blue)("mass of solute")) + overbrace("20 g")^(color(blue)("mass of solvent")) = overbrace("20.5 g")^(color(blue)("mass of solution"))

Now, you know that you have $\text{0.5 g}$ of sodium chloride in $\text{20.5 g}$ of solution, which means that $\text{100 g}$ of this solution will contain

100 color(red)(cancel(color(black)("g solution"))) * overbrace("0.5 g NaCl"/(20.5color(red)(cancel(color(black)("g solution")))))^(color(blue)("known composition")) = "2.439 g NaCl"#

Since a solution's percent concentration by mass, $\text{m/m %}$, tells you the number of grams of solute present for every $\text{100 g}$ of solution, you can say that your solution will be

$\textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{\text{% by mass = 2% NaCl}}}}$

The answer must be rounded to one significant figure, the number of sig figs you have for your values.