# Calculating the Formula of a Compound from Reacting Mass Data

## Understanding the Concept

• The formula of a compound can be deduced using the masses of the reactants.
• This approach is based on the conservation of mass principle, which states that the total mass of a chemical reaction’s reactants equals the total mass of products.

## Molar Ratios

• A chemical formula reflects the molar ratio of elements in a compound.
• The molar ratio is the ratio of the amounts (in moles) of each element in the reaction.

## Calculating Moles from Mass

• The number of moles of a substance can be calculated from its mass using the formula: Moles = Mass / Molar mass
• The molar mass (Mr) of an element or compound is the mass per mole.

## Balanced Equations and Molar Ratios

• A balanced chemical equation provides the molar ratio between the reactants and products.
• The coefficients (numbers in front of the reactants or products) in a balanced chemical equation indicate this molar ratio.

## Determining the Chemical Formula

• Once the moles of each reactant are known, their simplest ratio can be calculated to determine the formula.
• It might be necessary to round to the nearest whole number, as chemical formulas must consist of integer values.

## Example of Calculations

• For instance, if 2.00 g of hydrogen reacts with 16.00 g of oxygen to produce water, the molar amounts will be 1.00 mol of hydrogen and 1.00 mol of oxygen since H₂’s molar mass is about 2 g/mol and O₂’s molar mass is about 32 g/mol.
• This provides a molar ratio of 1:1, producing the formula H₂O.