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

1 Answer
Ernest Z.
Jun 18, 2017

The solution is 13.3 % #"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 #"KNO"_3#, but we don't know the mass of the water.

Calculate the mass of the water

#"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.

#"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 %#

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