When a 13.60-g sample of a compound containing only magnesium and oxygen is decomposed, 5.40 g of oxygen is obtained. What is the percent composition of this compound?

1 Answer
Dec 10, 2016

Answer:

#O: %# #=# #(5.40*g)/(13.60*g)xx100%=39.7%#

#Mg: %# #=# #(100-39.7)%=60.3%#

Explanation:

All we have done is to divide the elemental mass by the compound mass, and made it into a percentage.

We could also use these percentages to give an empirical formula. We assume that there are #100*g# of unknown compound.

And thus there are #(60.3*g)/(24.31*g*mol^-1)=2.48*mol# #Mg#, and likewise:

#(39.7*g)/(16.00*g*mol^-1)=2.48*mol# #O#.

We divide thru by the lowest molar quantity to give an empirical formula of #MgO#, as we would have expected.