Question

Question #8aa06

Answer 1

`"0.3 mol L"^(-1)`

Explanation:

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

`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.