# Question f2952

Oct 13, 2017

${\text{2.5 mol L}}^{- 1}$

#### Explanation:

The idea here is that in order to find the solution's molarity, you need to find the number of moles of potassium nitrate, the solute, present in exactly $\text{1 L} = {10}^{3}$ $\text{mL}$ of the solution.

To make the calculations easier, start with a sample of $\text{1 L} = {10}^{3}$ $\text{mL}$ of this 22%"m/m" potassium nitrate solution.

To find the mass of the sample, use the density of the solution.

10^3 color(red)(cancel(color(black)("mL solution"))) * "1.15 g"/(1color(red)(cancel(color(black)("mL solution")))) = "1150 g"

Now, you know that this solution is 22%"m/m" potassium nitrate, which means that every $\text{100 g}$ of this solution will contain $\text{22 g}$ of solute.

This implies that you sample will contain

1150 color(red)(cancel(color(black)("g solution"))) * "22 g KNO"_3/(100color(red)(cancel(color(black)("g solution")))) = "253 g KNO"_3

Next, convert the number of grams of potassium nitrate to moles by using the compound's molar mass

253 color(red)(cancel(color(black)("g"))) * "1 mole KNO"_3/(101.103 color(red)(cancel(color(black)("g")))) = "2.5 moles KNO"_3#

Since this represents the number of moles of potassium present in $\text{1 L} = {10}^{3}$ $\text{mL}$ of this solution, you can say that its molarity will be

$\textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{{\text{molarity = 2.5 mol L}}^{- 1}}}}$

The answer is rounded to two sig figs.