# Question #8aa06

##### 1 Answer

#### Explanation:

A solution's **molarity** is supposed to express the number of moles of solute present **for every** **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 **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

#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

#color(darkgreen)(ul(color(black)("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.