Recall that the molecular formula gives the actual number of different elements in a given compound, meaning it gives us the real formula for the compound. The empirical formula, on the other hand, just gives us the relative number of those different elements in that same compound. Up to this point, we've learned to calculate the empirical formula when given either the masses or the percentages of those elements within that compound.
But how exactly would we determine the molecular formula for those same compounds? Well, here we have a chart, and in this chart we're talking about 3 compounds, glucose, octane, and salicylic acid. We're going to say that their empirical formulas are given as C1H2O1. Remember that there are subscripts of one and one. There we have C4H9 and C7H6O3. In order to determine their molecular formulas, we can use N factors.
N factors are just numbers that we can multiply the empirical formula by in order to determine the molecular formula. So for example, glucose has an N factor of 6. That means I will multiply each of the subscripts of the empirical formula by 6 and that'll give me my molecular formula. So that would be 6 carbons, 12 hydrogens, and six oxygens. So the molecular formula of glucose is C6H12O6.
Octane has an N factor of 2, so multiplying those subscripts gives me C8H18. And then finally, salicylic acid has a factor of 1, which means that the molecular formula and empirical formula are the same. So just remember, when you're given the N factor, just multiply the empirical formula by it and you'll determine what your molecular formula will be.
But what happens when we don't have the N factor? How do we determine it? In the next series of videos, we'll go through the different steps required to find the different N factors for any given compound once you've determined its empirical formula.