Molecular Formulas!

For our final lesson in this unit, we spent about ten minutes learning molecular formulas. Then, we spent the rest of the class studying for our test on Thursday. This topic is really quite simple if you already understand the previous lesson. Let's get to it!




Molecular formulas tell us exactly how much of each atom are in a compound. If we know the empirical formula and the molar mass, we can easily determine the molecular formula. Here is yet another chart to help us write a molecular formula:

That really is all there is to it! Told you it was easy! Now for some examples:

EXAMPLES:
-The empirical formula for a substance is CH₂O and its molar mass is 60.0g/mol. Determine the molecular formula.

Simply find the molar mass of the empirical formula using your periodic table. You should arrive at 30.0g/mol. Then, divide 60 by 30, and you should arrive at 2. So, multiply all of the subscripts in the empirical formula by 2 to arrive at the molecular formula, C₂H₄O₂.

-The empirical formula for a compound is C₂H₆O and the molar mass is 138g/mol. Determine the molecular formula.

Simply find the molar mass of the empirical formula using your periodic table. You should arrive at 46g/mol. Then, divide 138 by 46, and you should arrive at 3. So, multiply all of the subscripts in the empirical formula by 3 to arrive at the molecular formula, C₆H₁₈O₃.

 
Next time: Unit 3 Test! (Study hard!)