Calculate the mass fraction of hydrogen: a. in water b. In Methane CH4

Formula for calculating the mass fraction of an element in a substance:
w = n * Ar (chemical element) / Mr (substance), where n is the number of atoms of a given chemical element.

A) 1) Find the relative molecular weight of the substance (H2O):
Mr (H2O) = 2 * Ar (H) + Ar (O) = 2 + 16 = 18
2) Find the mass fraction of this element in the substance:
w (H) = 2/18 = 0.11 or 11%

B) 1) Find the relative molecular weight of the substance (CH4):
Mr (CH4) = Ar (C) + 4 * Ar (H) = 12 + 4 = 16
w (H) = 4/16 = 0.26 or 25%
Answer: A) Mass fraction of hydrogen in water is 11%. B) Mass fraction of hydrogen in methane 25%.