# What is the percent by mass of a solution that contains 45.0 g "KNO"_3 in 295 mL water?

Jun 18, 2017

The solution is 13.3 % ${\text{KNO}}_{3}$ by mass.

#### Explanation:

The formula for percent by mass is

color(blue)(bar(ul(|color(white)(a/a)"% by mass" = "mass of component"/"total mass" × 100 %color(white)(a/a)|)))" "

We know the mass of the ${\text{KNO}}_{3}$, but we don't know the mass of the water.

Calculate the mass of the water

$\text{Mass of water" = 295 color(red)(cancel(color(black)("mL water"))) × "0.997 g water"/(1 color(red)(cancel(color(black)("mL water")))) = "294.1 g water}$

Now we can calculate the percent by mass.

$\text{Total mass = 45.0 g + 294.1 g = 339.1 g}$

"% by mass" = (45.0 color(red)(cancel(color(black)("g"))))/(339.1 color(red)(cancel(color(black)("g"))))× 100 % = 13.3 %