Question

What volume (in mL) of 30% (by mass) H2O2 is needed to prepare 25.0 mL of 3.6 M H2O2?

Answer 1

first find out the molarity of 30% H2O2

he has given 30% by mass that means 30 grams H2O2 present in 100 gram water

first calculate the moles of H2O2

moles of H2O2 = weight of H2O2 / molar mass of H2O2

moles of H2O2 = 30 gr / 34

= 0.88 moles

volume of the solution 100 gram

use the density = mass / volume

volume = mass / density (density of 30% H2O2 = 1.11

volume = 100 / 1.11

= 90.09 ml

= 0.09 L

now use the formula

Molarity = no of moles / volume in liters

Molarity = 0.88 / 0.09

Molarity = 9.77 M

now use the dilution formula M1V1 = M2V2

9.77 x V1 = 3.6 x 25.0

V1 = 9.2 mL of 30 % H2O2 required