Question #46792

1 Answer
Stefan V.
May 17, 2015

You can go from "m/v%" to molarity by using the number of moles of solute, in your case sodium hydroxide.

A mass by volume percent concentration solution is defined as grams of solute per 100 mL of solution, and multiplied by 100

"%m/v" = "grams of solute"/"100 mL solution" * 100

If you assume a volume of 100 mL of solution, which would make the calculations easier, you'd get

5 = m_(NaOH)/"100 mL" * 100 => m_(NaOH) = (5 * 100)/100 = "5 g NaOH"

This means that each 100 mL of solution contains 5 grams of sodium hydroxide. Use sodium hydroxide's molar mass to see how many moles you'd get

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

This would make the solution's molarity be

C = n/V = "0.125 moles"/(100 * 10^(-3)"L") = "1.25 M"

SIDE NOTE Don't forget that molarity is defined as moles of solute per liters of solution, that's why I converted 100 mL to L in the above equation.

Related questions
See all questions in Percent Concentration
Impact of this question
11248 views around the world
You can reuse this answer
Creative Commons License