Use ammonia \(\left(\mathrm{NH}_{3}\right)\) to explain what is meant by the percent composition by mass of a compound.

At the heart of chemistry lies the concept of atomic mass, which is essentially the weight of an individual atom of an element. It's measured in atomic mass units (amu), or grams per mole when dealing with larger, macroscopic quantities.
Atomic mass takes into account the protons and neutrons in the nucleus, since electrons contribute negligibly due to their much smaller mass. Each element has its atomic mass listed on the periodic table, providing a handy reference for various calculations in chemistry.
For example, as we see in our exercise, nitrogen (N) has an atomic mass of 14 amu, while hydrogen (H) is much lighter, being approximately 1 amu. This atomic mass is crucial for understanding the composition of molecules and carrying out calculations such as the determination of the percent composition by mass of a compound.

Molar mass represents the mass of one mole of a substance and is expressed in grams per mole (g/mol). It is a crucial figure in chemistry that helps in converting between the mass of a substance and the number of moles present.
In our exercise, calculating the molar mass of ammonia (NH₃) involves adding the atomic masses of its constituent elements—nitrogen and hydrogen. We multiply the atomic mass of hydrogen by three since there are three hydrogen atoms in each molecule of ammonia. The sum provides us with the molar mass of ammonia, which is 17 g/mol (14 g/mol from nitrogen and 3 g/mol from hydrogen).
Understanding the molar mass is not only key to mastering stoichiometry but is also fundamental when calculating the percent composition by mass of ammonia, which illustrates how much of the compound's mass comes from each element.

Chemical composition calculations give us detailed insights into the makeup of compounds in terms of the mass percentage of each constituent element. The percent composition by mass is a ratio of the mass of each element to the total molar mass of the compound, multiplied by 100 to get a percentage.

Step-by-Step Example

Firstly, we determine the molar mass of the compound, as we did with ammonia. Subsequently, we calculate the mass of each element in one mole of the compound; for ammonia this was 14g for nitrogen and 3g for hydrogen. The percent composition is then the mass of the individual element divided by the total molar mass of the compound, times 100.
Through this process, we learn that ammonia is composed of 82.35% nitrogen and 17.65% hydrogen by mass. These calculations are indispensable for chemists as they allow for the analysis of chemical formulas, the design of chemical reactions, and the determination of formula weights, which are fundamental aspects of chemical research and application.