Methane whole-number mass

If we know the molar mass of a compound, we can use the empirical formula to obtain the molecular formula, the actual number of moles of each element in 1 mol of compound. In some cases, such as water (H2O), ammonia (NH3), and methane (CH4), the empirical and molecular formulas are identical, but in many others the molecular formula is a whole-number multiple of the empirical formula. Hydrogen peroxide, for example, has the empirical formula HO and the molecular formula H2O2. Dividing the molar mass of H2O2 (34.02 g/mol) by the empirical formula mass (17.01 g/mol) gives the whole-number multiple ... 

The empirical formula of a compound is the simplest whole number ratio of the atoms it contains (Chapter 1). For some alkanes, methane and propane for instance, the empirical formula is the same as the actual molecular formula. However, for others this is not true. The empirical formula of ethane, whose molecular formula is C2Hg, is CHj. In practical terms the empirical formula is the formula that can be derived from the percentage composition data obtained from combustion analysis. In order to use this to establish the actual formula, data on the relative molecular mass (M ) of the compound is required. 

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