How many times is a water molecule heavier than a hydrogen molecule and lighter than an oxygen molecule?

1. Let’s calculate the relative molecular weights of the presented substances:

Mr (H2O) = 2 * Ar (H) + Ar (O) = 2 * 1 + 16 = 18;

Mr (H2) = 2 * Ar (H) = 2 * 1 = 2;

Mr (O2) = 2 * Ar (O) = 2 * 16 = 32;

2. we find the ratio of the molecular weight of water to the molecular weight of hydrogen, and oxygen to water, that is, we calculate the relative densities:

DH2 (H2O) = Mr (H2O): Mr (H2) = 18: 2 = 9;

DH2O (O2) = Mr (O2): Mr (H2O) = 32: 18 = 1.78.

Answer: A water molecule is 9 times heavier than a hydrogen molecule, and 1.78 times lighter than an oxygen molecule.