Which is heavier, methane or oxygen? Calculate the relative oxygen density of methane.

Given:
Methane – CH4
Oxygen – O2

To find:
CH4 and O2 – which is heavier?
D O2 (CH4) -?

Decision:
1) Using the periodic system of D.I.Mendeleev, calculate the molar masses of CH4 and O2:
M (CH4) = Mr (CH4) = Ar (C) * N (C) + Ar (H) * N (H) = 12 * 1 + 1 * 4 = 16 g / mol;
M (O2) = Mr (O2) = Ar (O) * N (O) = 16 * 2 = 32 g / mol;
2) Compare the molar masses of CH4 and O2:
O2 is heavier than CH4;
3) Calculate the density of CH4 by O2:
D O2 (CH4) = M (CH4) / M (O2) = 16/32 = 0.5.

Answer: O2 is heavier than CH4; the CH4 O2 density is 0.5.