A nitrogen and oxygen containing molecule is decomposed into its elements. It is found to contain 14 g of nitrogen and 40 g of oxygen. What is the empirical formula of the compound?

1 Answer
Jan 27, 2016



In order to find a compound's empirical formula you must find the smallest whole number ratio that exists between the elements that are a part of this compound.

You know that your unknown compound contains #"14 g"# of nitrogen and #"40 g"# of oxygen.

Your first goal here will be to use the molar masses of these two elements to figure out how many moles of each you get in this sample.

#"For N: " 14 color(red)(cancel(color(black)("g"))) * "1 mole N"/(14.007color(red)(cancel(color(black)("g")))) = "0.9995 moles N"#

#"For O: " 40 color(red)(cancel(color(black)("g"))) * "1 mole O"/(15.9994 color(red)(cancel(color(black)("g")))) = "2.500 moles O"#

In order to find the mole ratio that exists between these two elements in the compound, divide both values by the smallest one

#"For N: " (0.9995 color(red)(cancel(color(black)("moles"))))/(0.9995color(red)(cancel(color(black)("moles")))) = 1#

#"For O: " (2.500 color(red)(cancel(color(black)("moles"))))/(0.9995color(red)(cancel(color(black)("moles")))) = 2.501 ~~ 2.5#

In order to correctly determine the empirical formula of the compound, you need the smallest whole number ratio that exists between these two elements.

To get that, simply multiply both values by #2#. This will get you

#("N"_1"O"_2.5)_2 <=> "N"_2"O"_5#