Question #8aa06

1 Answer
Mar 15, 2017

Answer:

#"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.