Question

A solution is 2.00% (w/w) in ethanol and has a density of 1.10g/mL. How many grams of this solution are required to be transferred into a 250.0mL volumetric flask (and then diluted with solvent) to make a new solution that is 2.50x10^-2 M in ethanol?

Answer 1

w/w % of ethanol = 2.00 %

Molarity = 10 x density x wt % / Molar mass

             = 10 x 1.10 x 2 / 46

             = 0.48 M

volume V2 = 250 ml

Molarity M2 = 2.50 x 10^-2 M

from M1 V1 = M2 V2

0.48 x V1 = 2.5 x 10^-2 x 250

V1 = 13 ml

mass of solution = density x volume

                           = 1.10 x 13

                          = 14.3 g