CHAPTER 3
CHEMICAL EQUATIONS AND STOICHIOMETRY
MOLECULAR
FORMULA
A CHEMICAL FORMULA
THAT SHOWS THE
ACTUAL NUMBER OF
ATOMS OF EACH
ELEMENT PESENT IN A
COUMPOUND
EMPIRICAL FORMULA

DEFINITION:A formula that shows the simplest ratio of atoms of an element
present in a compound.

E.g. Molecular formula of glucose:C6H12O6
empirical formula of glucose: CH20
RELATIONSHIP BETWEEN
MOLECULAR FORMULA
AND EMPIRICAL
FORMULA

TELLS HOW MANY
ATOMS OF EACH
ELEMENT ARE IN A
COMPOUND AND
EMPIRICAL FORMULA
TELLS YOU THE SIMPLEST
OR MOST REDUCED
RATIO OF ELEMENTS IN A
COMPOUND.
DETERMINING EMPIRICAL FORMULA
I.
Start with the number of grams of each element,given
in the problem
II.
Convert the mass of each element to moles
III.
Divide each mole value by the smallest number of
moles calculated
IV.
Round off to the nearest whole number.
Determine the empirical formula of a compound contains 2.1% H,65.3% O,and 32.6% of S
( H=1.0 , O=16.0 , S= 32.0 )
HYDROGEN
MASS ( GRAMS )
MOLE
SIMPLEST WHOLE
NUMBER RATIO
Thus,the empirical formula of the compound is
OXYGEN
SULPHUR
What is the empirical formula of a compound containing 60.0% sulphur and 40.0%
oxygen by mass.(S:32.0 , O:16.0 )
SULPHUR
MASS ( GRAMS )
MOLE
SIMPLEST WHOLE NUMBER
RATIO
OXYGEN