Empirical and Molecular Formula Chemistry

Empirical Formula

100

a chemical formula of a compound that gives the proportions of the elements present in the compound

What is the empirical formula?

200

Determine the empirical formula for a the unknown compound that has 66.4% Cu, 33.6% S

CuS

300

Find the empirical formula of a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen.

CH₂O

400

Determine the empirical formulas for an unknown compound that has 0.366 g Na, 0.220 g N, 0.752 g O

 NaNO₃

500

What is the empirical formula of a compound containing 60.0% sulfur and 40.0% oxygen by mass?

S₃O₄

Molecular Formula

100

It tells us the actual numbers of atoms and how many of each type of atom are present in a molecule.

Molecular Formula

200

11.25% C, 88.75% Cℓ; mol. wt. = 320

C₃Cℓ₈

300

TRUE OR FALSE 

An empirical formula is always the same as the molecular formula?

FALSE! A molecular formula is either the empirical formula or a multiple of the empirical formula.

400

65.45% C, 5.45% H, 29.10% O; mol. wt. = 110

C₆H₆O₂

500

Caffeine has the following composition: 49.48% of carbon, 5.19% of hydrogen, 16.48% of oxygen, and 28.85% of nitrogen. The molecular weight is 194.19 g/mol. Find out the molecular and empirical formula.

C₄H₅N₂O.

Percent Composition

100

Percent composition of oxygen in CO₂

What is 72.7%?

200

Percent composition of nitrogen in NH₃

What is 82.4%?

300

Percent composition of Na in NaNO₂

What is 33.33%?

400

Percent Composition of CO₃ in H₂CO₃

What is 96.75%?

500

Percent Composition of NO₃ in Mg(NO₃)₂

What is 83.53%?