An Introduction
to
MOLAR MASS
Section 5.2
MOLAR MASS
 Definition:
The mass in grams of
1 mol of a substance
 Symbol:
M or mm
 Unit: g/mol
Molar Mass of Atoms


Molar mass = Mass off the periodic
table (atomic mass), in grams
Means that 1 mole of an element IS
its atomic mass.
MOLAR MASS vs ATOMIC MASS
Element
Atomic Mass
Molar Mass
Hydrogen
1.01 µ
1.01 g/mol
Sodium
22.99 µ
22.99 g/mol
Gold
196.97 µ
196.97 g/mol
Indicates that 1 mole of gold Masses 196.97 g
MOLAR MASS (M) OF
COMPOUNDS
To find Molar mass (M)
of a compound
 Need  molar mass
(M) of each individual
element in the
compound
ELEMENTS (atoms)
make
COMPOUNDS (molecules)
CALCULATING M of compound

Ex 1: Calculate the M of H2O
M H 2O
= molar mass of H + molar mass of O
= 2(1.01g/mol) + 16.00g/mol
= 2.02g/mol + 16.00g/mol
= 18.02g/mol
CALCULATING M of compound

Ex 2: Calculate the M of BeO
M BeO
= MBe + MO
=9.01g/mol + 16.00 g/mol
= 25.01 g/mol
CALCULATING M of compound

Ex 3: Calculate the M of Ca3(PO4)2
M Ca 3( PO 4 ) 2
= MCa + MP + MO
= 3(40.08) + 2(30.97) + 8 (16.00)
= 310.18 g/mol
CONVERTING MASS TO MOLES
Divide by M


Mass (g)
Moles (mol)
n=m
M
Where n = moles (mol)
m = mass (g)
M = molar mass (g/mol)
CONVERTING MASS TO MOLES

Example 1 : How many moles of CH3COOH are in
a 236 g sample?
CONVERTING MOLES TO MASS
Multiply By M
MOLES (mol)

Mass (g)
m=nxM
Where
n = moles (mol)
m = mass (g)
M = molar mass (g/mol)
CONVERTING MOLES TO MASS
Example 2: What is the mass of
5.67 x 1024 molecules of cobalt (II) chloride

HOMEWORK
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