Question #8aa06

1 Answer
Stefan V.
Mar 15, 2017

"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.

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