Question

Composition of Compounds Calculate the mass percent composition of nitrogen in each nitrogen- containing compound. $$ \text { a. }\mathrm{N}_{2} \mathrm{O} \quad \text { b. NO } \quad \text { c. } \mathrm{NO}_{2} \quad \text { d. HNO }_{3} $$

Short answer

The mass percent compositions of nitrogen are approximately 63.65% in N2O, 46.68% in NO, 30.43% in NO2, and 22.22% in HNO3.

Step-by-step solution

Calculate the molar mass of each compound

Find the atomic masses of nitrogen (N) and oxygen (O) from the periodic table. Nitrogen has an atomic mass of approximately 14.01 g/mol, and oxygen has an atomic mass of approximately 16.00 g/mol. Calculate the molar mass of each compound by summing the atomic masses of its elements based on the number of atoms of each element in the compound.

Determine the mass of nitrogen in each compound

Multiply the atomic mass of nitrogen by the number of nitrogen atoms in the compound to find the total mass of nitrogen in one mole of the compound.

Calculate the mass percent composition of nitrogen

Divide the total mass of nitrogen in the compound by the molar mass of the entire compound, obtained in Step 1. Multiply the result by 100 to convert it to a percentage. This gives the mass percent composition of nitrogen for each compound.

Apply the calculations to each compound

Repeat Steps 1 to 3 for each given compound: (a) N2O, (b) NO, (c) NO2, and (d) HNO3 to find their mass percent compositions of nitrogen.

Key concepts

Molar Mass Calculation

Understanding molar mass calculation is essential for anyone studying chemistry. Molar mass is the mass of one mole of a substance, and it's typically expressed in grams per mole (g/mol). It's calculated by adding up the atomic masses of each element in a compound, multiplied by the number of atoms of that element present.

For instance, water (H₂O) has a molar mass that is the sum of the atomic masses of two hydrogen atoms (1.008 g/mol each) and one oxygen atom (16.00 g/mol). This would give water a molar mass of approximately 18.02 g/mol. The molar mass enables us to convert between the mass of a substance and the amount of substance in moles, a key step in many stoichiometry problems.

Atomic Mass

The concept of atomic mass is fundamental to the calculations in chemistry. It represents the mass of a single atom and is measured in atomic mass units (amu). Each element's atomic mass can be found on the periodic table; it's based on a weighted average of the masses of an element's isotopes and their relative abundance.

For example, carbon has an atomic mass of approximately 12.01 amu because it is composed primarily of two isotopes: carbon-12 and carbon-13. Students need to understand atomic mass to calculate the molar mass of compounds and to determine the ratios in which elements combine to form compounds.

Percent Composition by Mass

Understanding percent composition by mass is crucial for analyzing the makeup of compounds. It expresses the mass of each element relative to the total mass of the compound as a percentage. To find the percent composition by mass, you divide the mass of the element in the compound by the total molar mass of the compound and multiply by 100%.

This concept is not only useful in stoichiometry but also in determining the purity of a compound and formulating chemical equations. Students need to grasp this concept to accurately describe the composition of substances and to predict the outcomes of chemical reactions.

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative relationship between reactants and products in a chemical reaction. It involves using the balanced chemical equation to calculate the masses, volumes, and moles of reactants and products. Understanding stoichiometry is important for predicting the amounts of substances consumed and produced in reactions.

Key to stoichiometry is the concept of the mole, which allows for conversions between atoms or molecules and grams. By knowing the molar mass of the reactants and products, you can calculate how much of a reactant is needed to completely react with another reactant, or how much of a product will be formed from given amounts of reactants.