An oxide of chromium is found to have the following composition: 28.2% Cr and 71.8% O. How would you determine this compound's empirical formula?

1 Answer

Answer:

Change the % to grams, change grams to moles, and then find a mole ratio.

Explanation:

#28.2 % = 28.2 g# Cr.

#71.8 % = 71.8 g# O

If there were 100 grams of the compound 28.2 grams would be Cr and 71.8 grams would be oxygen.

# (28.2 g)/(52.0 g//mol) = 0.542 mol Cr#

#(71.8 g)/(16.0 g//mol) = 4.49 mol O#

To set up a ratio divide the moles Cr into the moles O

#4.49/0.542 = 8.28 # round this off to a 8:1 ratio.

The empirical formula based on the data given would be

#CrO_8# which does not make sense chemically