Chemistry: Formula Mass and Percent Composition

Formula Mass

• Formula mass is the sum of the atomic masses of all atoms in a chemical formula.
• It is calculated by summing the atomic masses of each element in the formula, taking into account the number of atoms of each element.
• Formula mass is often used to calculate the molar mass of a compound.
• Formula mass units are typically in amu (atomic mass units) or g/mol (grams per mole).

Percent Composition

• Percent composition is the percentage of each element in a compound by mass.
• It is calculated by dividing the mass of each element in the formula by the formula mass, then multiplying by 100%.
• Percent composition can be used to determine the empirical formula of a compound.
• Percent composition is often expressed as a decimal value, with the percentage symbol (%) omitted.

Stoichiometry

• Stoichiometry is the study of the quantitative relationships between reactants and products in chemical reactions.
• It involves the use of chemical formulas and equations to calculate the amounts of substances required or produced in a reaction.
• Stoichiometry is based on the law of definite proportions, which states that a chemical compound always contains the same proportion of elements by mass, regardless of its source.
• Stoichiometric calculations often involve the use of mole ratios, which are the ratios of the number of moles of reactants to the number of moles of products.

Some common stoichiometric calculations include:

• Mole-to-mole conversions: using mole ratios to calculate the number of moles of a reactant or product.
• Mass-to-mass conversions: using mole ratios and molar masses to calculate the mass of a reactant or product.
• Limiting reactant problems: determining the amount of product formed when one reactant is completely consumed.
• Percent yield calculations: determining the percentage of the theoretical yield of a product that is actually obtained.

Formula Mass

• The formula mass of a chemical compound is the sum of the atomic masses of all its atoms.
• It is calculated by adding the atomic masses of each element in the formula, considering the number of atoms of each element.
• Formula mass is used to calculate the molar mass of a compound.
• Formula mass is typically expressed in amu (atomic mass units) or g/mol (grams per mole).

Percent Composition

• Percent composition is the percentage of each element in a compound by mass.
• It is calculated by dividing the mass of each element in the formula by the formula mass, then multiplying by 100%.
• Percent composition is used to determine the empirical formula of a compound.
• Percent composition is often expressed as a decimal value without the percentage symbol (%).

Stoichiometry

• Stoichiometry is the study of the quantitative relationships between reactants and products in chemical reactions.
• It involves using chemical formulas and equations to calculate the amounts of substances required or produced in a reaction.
• Stoichiometry is based on the law of definite proportions, which states that a chemical compound always contains the same proportion of elements by mass, regardless of its source.
• Stoichiometric calculations often involve mole ratios, which are the ratios of the number of moles of reactants to the number of moles of products.

Stoichiometric Calculations

• Mole-to-mole conversions: use mole ratios to calculate the number of moles of a reactant or product.
• Mass-to-mass conversions: use mole ratios and molar masses to calculate the mass of a reactant or product.
• Limiting reactant problems: determine the amount of product formed when one reactant is completely consumed.
• Percent yield calculations: determine the percentage of the theoretical yield of a product that is actually obtained.

Learn about formula mass, its calculation, and its relation to molar mass, as well as percent composition of compounds. Understand the concept of atomic mass units and grams per mole.