Download Molecular Formula

EMPIRICAL AND MOLECULAR
FORMULA
MOLECULAR FORMULAS
A
molecular formula tells
exactly how many atoms of each
element are in a molecule.
 It
is a whole number multiple of
the empirical formula.
EMPIRICAL/MOLECULAR FORMULA
Empirical Formula
Molecular Formula
An empirical formula indicates
the simplest whole-number
ratio for a molecule
A molecular formula tells exactly
how many atoms of each element
are in a molecule.
**Not common**
Is a multiple of the empirical
formula
CH2
C2 H4
C5 H 10
 Using
ratios- think whole numbers
FIND THE EMPIRICAL FORMULA FOR…
C6H12O6
C6H12O2
N2H2
CH4
DETERMINING MOLECULAR FORMULA
FROM EMPIRICAL FORMULA
 Step
1: Actual molar mass ÷
empirical molar mass (find)
 Step 2: Multiply each subscript by
the answer from step one
**You need the actual molar mass of
the compound**
MOLECULAR FORMULA EXAMPLE
 Find
the molecular formula of a compound
with empirical formula of CH2O and
molar mass of 180.18g
.
A
brown gas has the empirical
formula of NO2. Its experimental
molar mass is 46 g/mol. What is its
molecular formula?
FINDING THE MOLECULAR FORMULA FROM
THE PERCENT COMPOSITION
 Step
1: Find empirical formula
 Step 2: Divide the molar mass of the
compound (given in the problem) by
the molar mass of the empirical
formula
 Step 3: Multiply each subscript by
the answer to Step 2
A COMPOUND HAS A MOLAR MASS IS 30.0
GRAMS AND A COMPOSITION IS 20.0 % H
AND 80.0% C?
1.
What is the empirical formula?
2.
What is the molecular formula?