CELEBRITY CHEMIST of THE DAY
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MOLE CONCEPT
Unit of measure for matter
Number of particles in one mole =
Avogadro’s number = 6.02 X 10 23
602 000 000 000 000 000 000 000
How many molecules are present in 4 moles
of H2O? How many atoms are present?
SOLUTION:
One mole of any substance contains 6.02 X 10 23
particles, therefore:
(4 moles) 6.02 X 10 23 = 2.41 X 10 24 molecules
mole
Since there are 3 atoms per H2O molecule,
the total number of atoms is:
(3 atoms) 2.41 X 10 24 molecules = 7.23 X 10 24 atoms
molecule
MOLAR MASS
Mass of one mole = mass of one
atom/molecule expressed in grams rather
than atomic mass unit (amu)
1 amu = based on 1/12 the mass of C-12 (most
common carbon isotope)
Example:
1 atom of He = 4 amus
1 mole of He = 4 grams
1 molecule of O2 = 2 x 16 amus/O = 32 amus
1 mole of O2 = 32 grams

FORMULA
NUMBER OF
=
MOLES
n
=
GIVEN WEIGHT
MOLAR MASS
GW
MM
1. How many moles of carbon
atoms are contained in 4 g of
carbon?
The atomic mass of carbon is 12 amu,
therefore the molar mass of carbon is 12
grams.
4g X
1 mole = 0.333 mole C
12 g
CONVERSION
FACTOR
(from periodic table)
2. How many moles of water are
there in 36 g of water?
SOLUTION:
The molecular mass of H2O is 18 amu.
The molar mass of H2O is 18 g.
36 g
X 1 mole = 2 moles H2O
18 g
3. Calculate the mass of aluminum
carbonate (Al2(CO3)3) in 5.85 moles
of the compound.
In Al2(CO3)3 , there are 2 Al, 3 C and 9 O
Formula mass = (2 X 27 g/Al) +
(3 X 12 g/C) + (9 X 16 g/O) = 234 g
Molar mass = 234 g
Mass of Al2(CO3)3 = 5.85 moles X 234 g
= 1369 g
MOLAR VOLUME
Volume of one mole of solid and liquids = varies from one
substance to another based on their density
Example:
1 mole of H2O (density = 1.00 g/mL) has a mass of 18
grams and will therefore occupy 18 mL
1 mole of NaCl (density = 2.165 g/mL) has a mass 58 g
(Na = 23 g + Cl = 35 g) and would occupy a
volume of 26.8 mL (58 g /2.165 g/mL)
Volume of one mole of gas =equal to 22.4 liters at standard
temperature (0oC) and pressure (1 atm or 760 mm Hg)
(STP)
1 mole of O2 gas = 22.4 L at STP
1 mole of He = 22.4 L at STP
1. How many moles of nitrogen are
present in 4.48 liters of nitrogen
at STP?
Since there are 22.4 liters of any gas at
STP, the solution is
4.48 L X 1 mole = 0.2 moles N2
22.4 L
CONVERSION
FACTOR
PERCENT COMPOSITION
-
Percent by mass of each element
present in the compound.
% by
mass of
each
element
Total mass of element X 100%
=
Total mass of compound
What is the percentage composition
of H2O?
% H in
2 X 1 g x 100% =
=
H2O
18 g
11.11 %
% O in
1
X
16
g
x
100%
=
=
H2O
18 g
88.89%
TO CHECK =
100.00%