Question

Please explain

Answer 1

The empirical and molecular formulas deal with the NUMBER of atoms of each element in the compound. The question gives you the MASSES of each element. We therefore need to convert these masses into "numbers", and we can do that by converting to moles.

To find the number of moles of each element, divide the given masses by the corresponding molar mass. For nitrogen, we have 4.90 g / 14 g/mol = 0.35 mol, and for oxygen we have 11.2 g / 16 g/mol = 0.7 mol.

We can now find the RATIO of atoms of each element in the compound and thereby come up with the empirical formula. To do this, divide the moles of each element by the smallest number of moles you have. In this case, the smallest number of moles is 0.35, so you get 0.35/0.35 = 1 for nitrogen, and 0.7/0.35 = 2 for oxygen. This means that the ratio of N:O is 1:2, so the empirical formula is NO2.

We can determine the molecular formula since we're given the molar mass of the actual compound. The molar mass of the actual compound is 92 g/mol. If you calculate the molar mass of the empirical formula we just found, you'll see it's only 46 g/mol. Divide the actual molar mass by the empirical molar mass to find the factor we're off by: 92 g/mol / 42 g/mol = 2. This means that the molecular formula actually contains twice as many of each atom - in other words, the molecular formula of this compound is N2O4.

Let me know if that makes sense or if you need me to clarify anything!

Answer 2

Thank you this was very helpful. I might have another question and ill tag you:)