Chem Catalyst
Calculate the percent composition of ibuprofen (C
13
H
18
O
2
)

1.
2.
3.
4.
Today’s Agenda:
Catalyst
Finish Notes- Empirical Formula
Practice Problems
HW: p. 312 #45-46

Chemical Formulas:
Empirical formula: the lowest whole-number ratio of the atoms of elements in a compound
Molecular formula: the exact number of atoms of elements in a compound
For example, styrene (C
2
H
2
), and acetylene (C
8
H
8
) have different molecular formulas but the same empirical formula (CH)

Finding Empirical Formulas:
Determining the MOLE RATIO of elements in a compound.
1. Find percent composition (if not given)
2. Divide percent composition by molar mass of element to get mole ratios
3. Simplify to whole numbers by dividing all mole ratios by the smallest one
4. Write the formula with the subscripts

Empirical Formula: Example
A compound contains 25.9% nitrogen, and 74.1% oxygen. What is the empirical formula of this compound?

Empirical Formula: Example
Calculate the empirical of these compounds:
1) 94.1% O, 5.9% H
2) 67.6% Hg, 10.8% S, 21.6% O

Molecular Formula: Example
A compound has an empirical formula CH and a molar mass of 104.2 g/mol. What is its molecular formula?
1.
2.
Divide the molar mass of the empirical formula by molar mass of the molecular formula.
Multiply all subscripts by that value.

Molecular Formula: Example
A compound has an empirical formula CH and a molar mass of 104.2 g/mol. What is its molecular formula?

Empirical Formula: Example
Calculate the empirical formula of these compounds:
3) 36.1% Ca, 63.9% Cl
2) 40.0% C, 6.7% H, 53.3% O