# Question 8aa06

Mar 15, 2017

${\text{0.3 mol L}}^{- 1}$

#### Explanation:

A solution's molarity is supposed to express the number of moles of solute present for every $\text{1 L}$ of solution, so the first thing to do here is to convert the mass of sodium hydroxide to moles.

To do that, use the compound's molar mass

5 color(red)(cancel(color(black)("g"))) * "1 mole NaOH"/(40.0color(red)(cancel(color(black)("g")))) = "0.125 moles NaOH"

So, you know that this solution contains $0.125$ moles of solute in

500 color(red)(cancel(color(black)("mL"))) * "1 L"/(10^3color(red)(cancel(color(black)("mL")))) = "0.5 L"

of solution, which means that $\text{1 L}$ of this solution will contain

1 color(red)(cancel(color(black)("L solution"))) * "0.125 moles NaOH"/(0.5color(red)(cancel(color(black)("L solution")))) = "0.25 moles NaOH"#

You can thus say that the molarity of the solution is equal to

$\textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{{\text{molarity = 0.3 mol L}}^{- 1}}}}$

The answer must be rounded to one significant figure, the number of significant figures you have for the mass of sodium hydroxide and for the volume of the solution.