Question: use ammonia to explain what is meant by the percent composition by mass of a compound?
Answer: The percent composition is the percent by mass of each element in a compound. One mole of ammonia (NH3) contains one mole of nitrogen (N) atom and 3 moles of hydrogen (H) atoms. ... Thus, the molar mass of NH3 is the sum of the atomic masses of N and 3 times the molar mass of H.