# Question 203f7

Aug 15, 2016

See explanation.

#### Explanation:

The thing to remember about molarity is that you can use it as a conversion factor to go from moles of solute to liters of solution and vice versa.

As you know, molarity is defined as moles of solute present in exactly one liter of solution. In your case, a molarity of $\text{2.50 M}$ tells you that for that particular solution, one liter of solution contains $2.50$ moles of solute.

$\text{2.50 M" = "2.50 mol L"^(-1) = "2.50 moles"/"1 L solution}$

This means that if you know the volume of the solution, let's say $\text{0.75 L}$, you can use its molarity to find the number of moles of solute it contains

0.75 color(red)(cancel(color(black)("L solution"))) * "2.50 moles NaOH"/(1color(red)(cancel(color(black)("L solution")))) = "1.88 moles NaOH"

Similarly, if you know the number of moles of solute present in your sample, let's say $0.625$ moles, you can use its molarity to find the volume of solution that would contain that many moles

0.625 color(red)(cancel(color(black)("moles NaOH"))) * "1 L solution"/(2.50 color(red)(cancel(color(black)("moles NaOH")))) = "0.250 L solution"#