Empirical and Molecular Formulas

October 4th, 2012 

Hi everyone, I forgot to post yesterday and we did not really do anything today except take a homework quiz and work on the Web Assign review, so I will just go over what we did yesterday. Yesterday we learned about...

EMPIRICAL AND MOLECULAR FORMULAS!!

-Empirical formulas are the simplified formulas, which give the whole number ratio of the atoms in a compound-(example: H2O2 becomes HO)
               -always in whole numbers
               -can be the same as molecular formula


-Molecular formulas represent the total number of atoms per element in a compound

This might help you understand the difference between the two.

How to find the Empirical and Molecular Formulas If you have the percent of each element in a compound, assume that it is 100g, so that the percent is also the number of grams Convert the mass of each element to moles using the molar mass from the periodic table.  Divide each mole value by the smallest number of moles calculated.  Round to the nearest whole number These numbers make the subscripts for each element in the empirical formula Here is an example problem:

So in this problem, the empirical formula would be C14H18N2O5

Finding the molecular formula is very simple once you have found the empirical formula...

1. Find the molar mass of the empirical formula by using the periodic table

2. Divide the molar mass of the compound (which should be given to you) by the molar mass of the empirical formula 

3. Round the number from step 2 to the nearest whole number and multiply it by the subscripts for each atom in the empirical formula to get the molecular formula 

OK.....that's it. So here are the reminders....

Homework:

-study for unit 2 test 

-finish all web assigns 

THE NEXT SCRIBE IS.... ZACK 

Works cited: http://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm