Wake-up

1. Determine the empirical formula for the following: 28.4% Copper and 71.6% Bromine

Molecular Formula

What are Molecular Formulas?How to calculate molecular formulas?

Empirical FormulaA chemical formula that shows the lowest whole

number ratio of all atoms in a compound

Molecular FormulaA chemical formula that shows the total number

and kinds of atoms in a molecule

Recall from yesterday

Compound A is Empirical Formula

Compound B is Molecular Formula

How to find Molecular Formulas?1. Write down what you know.

The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of

butane?

Empirical formula = C2H5

Molar Mass = 60g/mol

How to find Molecular Formulas?2. Calculate/Find the Empirical Formula

(if needed)

C2H5

The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of

butane?

How to find Molecular Formulas?3. Calculate the empirical formula mass (efm)

using the empirical formula

C = 2 x 12.01 = 24.02H = 5 x 1.00 = 5

Empirical Formula Mass = 24.02 + 5

29.02

How to find Molecular Formulas?4. Divide the molar mass (that is provided in the

problem) by the empirical formula mass

The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of

butane?

60g/mol29.02g = 2 mole

How to find Molecular Formulas?5. Multiply the empirical formula subscripts by

the whole number you found in step 4 to get the molecular formula.

C2H5 x 2 = C4H10

Example #1The simplest formula for vitamin C is C3H4O3.

Experimental data indicates that the molecular mass of vitamin C is about 180 g/mol. What is

the molecular formula of vitamin C?

Example #2A compound contains 18.8% sodium, 29%

chlorine, and 52.2% oxygen, by mass. If the molar mass of the compound in 122.44 g/mol,

determine the empirical and molecular formulas.

Example #3Caffeine has an elemental analysis of 49.48%

carbon, 5.190% hydrogen, 16.47% oxygen, and 28.85% nitrogen. It has a molar mass of 194.19

g/mol. What is the molecular formula of caffeine?

Molecular Formula

What are Molecular Formulas?How to calculate molecular formulas?