unit v: the mole concept v.5. empirical and molecular formulae

Unit V: The Mole Concept

V.5. Empirical and Molecular Formulae

Empirical Formula

Empirical Formula Simplest Formula Gives the simplest whole number ratio of

elements in a compound

Molecular Formula

Molecular Formula Gives the ACTUAL number of each kind of atom

in a molecule and compound

Molecular vs. Empirical

Molecular vs. Empirical

Molecular Formula Empirical Formula

P4O10

C10H22

C6H18O3

C5H12O

N2O4

Molecular vs. Empirical

Molecular Formula Empirical Formula

P4O10 P2O5

C10H22 C5H11

C6H18O3 C2H6O

C5H12O C5H12O

N2O4 NO2

Finding Empirical Formulas

A sample of an unknown compound is analyzed and found to contain 8.4 g of “C” 2.1 g of “H” and 5.6 g of “O”.

Find the empirical formula.

Finding Empirical Formulas

Element Mass (g)

AtomicMass

Moles MolesSm.Moles

SmallestRatio

C

H

O

Finding Empirical Formulas

0.888 grams of a compound made up of carbon, hydrogen and oxygen are found to contain 0.576 g of carbon and 0.120 g of hydrogen.

a) Find the mass of oxygen

b) Find the empirical formula

Finding Empirical Formulas

Element Mass (g)

AtomicMass

Moles MolesSm.Moles

SmallestRatio

C

H

O

Finding Empirical Formulas

A while powder used in paints has the following composition:

Ba 69.58% C 6.090% O 24.32%

Find the Empirical Formula

Finding Empirical Formulas

Element Mass(g) AtomicMass

Moles MolesSm.Moles

SmallestRatio

Ba

C

O

WHAT HAPPENS WHEN…….. is not near a whole # __ Moles__

smallest moles

If ends in

a decimal of

Multiply ALL numbers by…. to get the Smallest

Ratio

≈ 0.5 2

≈0.33 or ≈0.66 3

≈0.25 or ≈0.75 4

≈0.2, ≈0.4, ≈0.6, ≈0.8 5

molessmallest

moles

Empirical to Molecular Formula A compound has a molar mass of 60.0g/mol and its

empirical formula is CH2O. Find the molecular formula.

Empirical Molecular

Formula

Mass

Hebden

Do Exercises 46 (d, g, & m) on pages 93 & Exercises 48 and 52 on page 95 of Hebden

Read through Tutorial 5-1: Percent Mass and Empirical Formulas (Working in Pairs)

Do the Self-Test on Tutorial 5-1