# What is the percent by mass of KBr if 58.2 grams are dissolved in 344 grams of water?

Apr 20, 2018

14.5%

#### Explanation:

The idea here is that you need to determine how many grams of potassium bromide will be present for every $\text{100. g}$ of this solution, which is what the solution's percent concentration by mass represents.

If you dissolve $\text{58.2 g}$ of potassium bromide in $\text{344 g}$ of water, the total mass of the solution will be

$\text{58.2 g + 344 g = 402.2 g}$

So this solution contains $\text{58.2 g}$ of potassium bromide in $\text{402.2 g}$ of the solution, which means that in $\text{100. g}$ of this solution you will have

100. color(red)(cancel(color(black)("g solution"))) * "58.2 g KBr"/(402.2 color(red)(cancel(color(black)("g solution")))) = "14.5 g KBr"

You can thus say that the solution's percent concentration by mass is equal to

$\textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{\text{% m/m = 14.5% KBr}}}}$

The answer is rounded to three sig figs, the number of sig figs you have for your figures.

Apr 20, 2018

The percent by mass of $\text{KBr}$ is $\text{14.4%}$.

#### Explanation:

"%(m/m)"=("mass of solute")/("mass of solution")xx100

The mass of the solution is the mass of the solute and solvent.

The given mass of the solute $\text{KBr}$ is $\text{58.2 g}$.

The mass of the solution is $\text{58.2 g KBr + 344 g H"_2"O"="404.2 g}$

Plug in the known values and solve.

"%(m/m)"=(58.2"g KBr")/(404.2"g solution")xx100=14.4%