A compound weighing 115 g contains 68.3 g of carbon, 13.2 g of hydrogen, 15.9 g of nitrogen, and some amount of oxygen. What is the mass percent of oxygen in the compound?

1 Answer
anor277
May 8, 2016

The balance, the mass that is not accounted for by carbon, hydrogen, and nitrogen is taken to be oxygen.

Explanation:

An analyst will typically report #%C; %H; %N#. If these percentages do not sum to #100%#, the balance is taken to be oxygen.

Why? Because it is fairly difficult to measure oxygen (especially as the atmosphere is some 30% dioxygen).

Given this, the mass of oxygen present in your sample is:

#[(115-68.3(C)-13.2(H)-15.9(N)]%# #=# #17.6*g#

Thus #%O# #=# #(17.6*g)/(115*g)xx100%# #=# #??%#

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