How to calculate the mass fraction of carbon and hydrogen in methane?

Given:
CH4

Find:
ω (C in CH4) -?
ω (H in CH4) -?

Solution:
1) Using the periodic system of D.I.Mendeleev, calculate the relative molecular weight of CH4:
Mr (CH4) = Ar (C) + Ar (H) * 4 = 12 + 1 * 4 = 16;
2) Calculate the mass fraction of C in CH4:
ω (C in CH4) = N (C) * Ar (C) * 100% / Mr (CH4) = 1 * 12 * 100% / 16 = 75%;
3) The methane molecule consists of two chemical elements. Calculate the mass fraction of H in CH4:
ω (H in CH4) = 100% – ω (C in CH4) = 100% – 75% = 25%.

Answer: Mass fraction of C in CH4 is 75%; H in CH4 – 25%.