Question

What is the molecular formula of a compound if its empirical formula is `NO_2` and its molar mass is 138.02 g/mole?

Answer 1

138.02 g/mol `-:` molar mass of empirical formulae = whole number,
then
Molecular Formulae = Empirical Formulae `xx` whole number

Explanation:

If the molar mass of 138.02 g/mol has been provided for you,
divide it by the molar mass of `NO_2`.

Nitrogen has a molar mass of 14.0 g/mol, whereas oxygen is 16.0 g/mol
138.02 g/mol `-:` `(1 xx 14.0 +2 xx16.0)`
138.02 g/mol `-:` 46.0 g/mol = 3.00 (rounded to nearest whole number)

Since 3.00 is the whole number, multiply it by the empirical formula.

(`NO_2`)`xx`3.00 = `N_3O_6` is the molecular formula.