USING MOLAR
CONVERSIONS TO
DETERMINE EMPIRICAL
AND MOLECULAR
FORMULAS
FORMULA OF A COMPOUND BASED ON
CHARGES
• PREDICTION:
• WHAT WOULD BE THE FORMULA FOR MAGNESIUM OXIDE?
FORMULA BASED ON DATA:
• Empirical formula: Reduced formula.
• Ex. CH2O
• Molecular formula: Not reduced formula; must take
into account atomic mass!
• Ex. C6H12O6
Empirical or Molecular?
P2Cl6
PCl5
APPLICATION: WHAT IS THE
MOLECULAR FORMULA?
• A compound has a molecular mass of 132 g/mol
and an empirical formula of CH2NO. What is its
molecular formula?
HOW TO FIND EMPIRICAL
FORMULA
• Change % to grams (if the % add up to 100)
• Change grams to moles.
• Find the mole ratio by dividing by the smallest
number.
• Change the ratio to a whole # ratio by multiplying
by a common multiple.
• Use the ratio as the subscripts in the formula.
FIND THE EMPIRICAL FORMULA OF:
• #1 A compound made of magnesium and oxygen
that has a total mass of 5 grams and was made by
reacting 3 grams of magnesium metal.
• #2 A compound made of 75% magnesium and 25%
oxygen.
ANOTHER EMPIRICAL FORMULA
QUESTION
• Example Problem #2
• NutraSweet is 57.14% C, 6.16% H, 9.52% N, and
27.18% O. Calculate the empirical formula of
NutraSweet (The molar mass of NutraSweet is
294.30 g/mol)
TO FIND MOLECULAR FORMULA:
• Find the mass of the empirical formula of the
molecule.
• Divide the mass of the molecular formula weight by
the empirical formula:
• If they are the same (1): the empirical formula IS the
molecular formula.
• If they are not the same: multiple each atom in the
empirical formula by the number you got when you
divided.
MOLECULAR FORMULA OF
NUTRASWEET
• (The molar mass of NutraSweet is 294.30 g/mol)
• What is the molecular formula?
EMPIRICAL AND MOLECULAR
FORMULA
• The sample contains 2.143g of carbon and 0.358g of
hydrogen.
•
•
•
•
What is the total molecular weight of this compound?
Find the empirical formula.
Find the mass of the empirical formula.
What is the molecular formula of this compound?