JE #___: Stoichiometry “Particle” Problems
 If number of particles (atoms, ions, molecules or formula units) are
involved, 2 alternate steps may be needed to complete the problem
# of
part.of
known
moles
of
known
moles
of
unknown
mass
of
known
# of
part. of
unknown
mass
of
unknown
Ex: “How many grams of C5H8 form 1.89 x 1024 molecules of C5H12?”
C5H12(l)  C5H8 + 2 H2
1. Starting Point
given: 1.89 x 1024 molecules of C5H12
box: “# of particles of known”
2. Ending Point
unknown: grams of C5H8
box: “mass of unknown”
3. Set up picket fence and follow through
1.89 x 1024 molc. C5H12 1 mol C5H12
6.022 x 1023
molc. C5H12
1 mol C5H8
68.13g C5H8
= 21.3825 x 101 or
1 mol C5H12
1 mol C5H8
214g C5H8
  
Avo’s #
mole ratio
molar mass