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
1.
2.
3.
4.
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
1. Find empirical formula.
2. Find M of empirical formula
3. Divide molar mass in question by this
number.
4. Multiple empirical formula by this result.
5. Write molecular formula.
Calculating Masses of Reactants and
Products
1. Write a balanced equation.
2. Calculate the amount, in mol, of the
substance with the known mass.
3. Use mole ratio to find amount, in mol, of
substance from question.
4. Answer the question…find the mass of this
substance.
Excess Reactants
1. Write a balanced equation.
2. Find the amount, in mol, of both reactants.
3. Determine which is in excess, using the mol
ratios.
4. Use limiting reagent to find mol of substance
in question.
5. Answer the question…find the mass.