Chapter 2 – Analysis by Mass

Gravimetric Analysis The quantitative analysis of substances based on the measurement of mass is called gravimetric analysis. It is also used to determine the chemical formula of a compound.

Empirical Formulas Chemical analysis enables us to determine the empirical formula of a compound. This is the simplest whole number ratio of the atoms present in the compound.

Finding the Empirical Formula Set up the ratio Find the moles of each substance Divide all results by the smallest number Write empirical formula

Molecular Formulas A molecular formula gives the actual number of atoms of each element present in a molecule of a compound. The molecular formula of a compound is not necessarily the same as the empirical formula.

Finding the Molecular Formula Find empirical formula. Find M of empirical formula Divide molar mass in question by this number. Multiple empirical formula by this result. Write molecular formula.

Calculating Masses of Reactants and Products Write a balanced equation. Calculate the amount, in mol, of the substance with the known mass. Use mole ratio to find amount, in mol, of substance from question. Answer the question…find the mass of this substance.

Excess Reactants Write a balanced equation. Find the amount, in mol, of both reactants. Determine which is in excess, using the mol ratios. Use limiting reagent to find mol of substance in question. Answer the question…find the mass.