Hydrogen Peroxide is H2O2 with a molar mass of 34.015 g/mole
A 30% solution of H2O2 is 30% H2O2 and 70% H2O by volume.
So a liter of this solution contains 0.30 liter of H2O2 and 0.70 liter
of H2O. The density of H2O2 is 1.44 g/cm^3 = 1.44 g / 0.001 liter.
0.30 liter of H2O2 has a mass of (0.30 liter)(1.44 g / 0.001 liter) =
432 g, which is 432 g / 34.015 g/mole = 12.70 moles of H2O2.
This means that a 30% H2O2 solution = 12.70 M H2O2