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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.
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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.