1
Stoichiometry:
Calculations with Chemical
Formulas and Equations
Chapter 3
Chapter 3
•
Chemical Equations
–
Balancing, Types of Equations
•
Compound Composition
–
Atom mass; Atomic and formula weight
–
% Composition
–
Empirical Formulas/Molecular Formulas
–
Mole ratio - Stoichiometry
•
Amounts in chemical reactions
–
Limiting reagents
–
Theoretical yield
–
Percent yield
Determining the
Empirical Formula
Can we determine the formula for a
compound from the % composition?
•
Empirical formula
←
% Composition
(mole ratio)
(mass ratio)
Determining the Empirical
Formula for a Compound
Given that the % composition of a compound
is 30.45% N
and 69.56% O
, what is the
empirical formula for the compound?
•
1.
Assume 100 g of compound
•
2.
Convert g of each element to moles.
•
3. Divide or multiply each by the same number to
get whole-number subscripts.
Determining the Empirical
Formula for a Compound
Given that the % composition of a compound
is 30.45% N
and 69.56% O
, what is the
formula for the compound?
•
1.
Assume 100 g of compound
30.45 g N
69.56 g O
Determining the Empirical
Formula for a Compound
Given that the % composition of a compound
is 30.45% N
and 69.56% O
, what is the
formula for the compound?
•
2.
Convert grams of each element to moles.
(30.45 g N)(1 mol/14.01g N) = 2.173 mol N
(69.56 g O)(1 mol/16.00g O) = 4.348 mol O

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