# Question a69e3

May 5, 2016

$\text{30% m/m}$

#### Explanation:

A solution's percent concentration by mass, $\text{%m/m}$, essentially tells you how many grams of solute you get in $\text{100 g}$ of solution.

This means that in order to find a solution's percent concentration by mass, you must determine how many grams of solute you have in $\text{100 g}$ of solution.

In your case, the solution is said to contain $\text{90 g}$ of calcium iodide, ${\text{CaI}}_{2}$, which is your solute, and have a total mass of $\text{300 g}$.

This means that $\text{100 g}$ of solution will contain

100 color(red)(cancel(color(black)("g solution"))) * "90 g CaI"_2/(300color(red)(cancel(color(black)("g solution")))) = "30 g CaI"_2

So, if $\text{100 g}$ of solution contains $\text{30 g}$ of solute, it follows that its percent concentration by mass will be equal to

"% m/m" = color(green)(|bar(ul(color(white)(a/a)"30%"color(white)(a/a)|)))#