Question

Question #f2952

Answer 1

`"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 `"1 L" = 10^3` `"mL"` of the solution.

To make the calculations easier, start with a sample of `"1 L" = 10^3` `"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 `"100 g"` of this solution will contain `"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 `"1 L" = 10^3` `"mL"` of this solution, you can say that its molarity will be

`color(darkgreen)(ul(color(black)("molarity = 2.5 mol L"^(-1))))`

The answer is rounded to two sig figs.