STOICHIOMETRY: MOLE-MOLE PROBLEMS
The types of mole problems investigated so far have been ones involving only one
substance. Chemical calculations often involve more than one substance and take
into consideration information found in balanced reaction equations discussed in
Chapter 4. Recall that coefficients from a balanced equation can be used to
describe the numbers of atoms, ions, or molecules involved in the chemical
process. Also recall that the quantities of each must balance on both sides of the
equation to satisfy the Law of Conservation of Matter. Those coefficients can also
represent larger numbers of particles, namely moles of those substances, that are
reacting or being produced. Therefore, the balanced chemical reaction
2NaClO(s) → 2NaCl(s) + O 2 (g)can be interpreted in two ways.
- Decomposing 2 formula units of sodium hypochlorite produces 2 formula
units of sodium chloride and 1 molecule of oxygen. - Decomposing 2 moles of sodium hypochlorite produces 2 moles of
sodium chloride and 1 mole of oxygen molecules.
Coefficients in balanced chemical reaction equations therefore provide mole
ratios for reacting substances and substances produced.
Example 1
How many moles of sodium chloride can be produced from 0.0253 moles of
sodium hypochlorite?
Use dimensional analysis:
Example 2
How many moles of sodium hypochlorite are needed to produce 0.750 moles of
oxygen?
Use dimensional analysis:
STOICHIOMETRY: MASS-MASS PROBLEMS
In order to work with substances in the laboratory, chemists must work with