- The mole concept allows chemists to conveniently keep track of large numbers of particles. A mole is defined as 6.02 x 1023 particles, whether atoms, molecules, ions, etc. - The formula mass (or molar mass) of a compound is the sum of the atomic masses of each element in its chemical formula. It has units of grams per mole (g/mol). - Calculations involving moles, mass, particles and formula mass allow conversions between the microscopic and macroscopic scales in chemistry.

1. THE
MOLE
CONCEPT

2. - 6.02 x 1023 is
Avogadro’s
number
- Equivalent to
one mole
AVOGADRO’S NUMBER

3. Mole (mol)is a measure of the amount
of particles in matter. It is the
chemists’dozen.
Mole is always represented by
Avogadro’s number 6.02 x 1023
1 molar mass of any substance contains one mole of particles
(ions, molecules, atoms, formula units)

4. • Mole = mass/molecular mass;
• Mole= no. of particles/Avogadro’s number
Example:
1 mole of Aluminum = 6.02 x 1023 atom

5. Is the sum of the masses of the atoms represented
in a formula:
If the formula represents a molecule, the term
molecular mass is often used.
Example: O2 specifies two oxygen atoms per molecule of
oxygen, the formula (or molecular mass) of oxygen (O2) is twice
the atomic mass of oxygen.
2 x atomic mass of O = 2 x 16.0 u = 32.0 u
FORMULA MASS

6. Calculate (a) the molecular mass of nitrogen
dioxide (NO2), an amber colored gas that is a
constituent of smog, and (b) the formula mass
of ammonium sulfate [(NH4)2SO4] a fertilizer
commonly used by home gardeners.
CALCULATING MOLECULAR MASS

7. 1. Calculate the formula mass of (a) sodium
azide (NaN3) used in automobile airbags, and
(b) phosphoric acid (H3PO4)
2. Find the formula mass of (a) para-
dichlorobenzene (C6H4Cl2)used as a moth
repellent, and (b) calcium dihydrogen
phosphate [Ca(H2PO4)2], used as a mineral
supplement in foods.
PRACTICE:

8. The molar mass of a substance is the mass of one
mole of that substance. It is numerically equal to the
atomic mass or formula mass, but is expressed in the
unit grams per mole (g/mol)
Example: 1 mol Na = 23.0 g Na
1 mol CO2 = 44.0 g CO2
1 mol (NH4)2SO4 = 132.1g (NH4)2SO4
MOLAR MASS

9. How many grams of N2 are in 0.400 moles N2?
Solution:
The molecular mass of N2 is 2 x 14.0 u = 28.0 u.
The molar mass of N2 is therefore, 28.0 g/mol. Using the
molar mass as a conversion factor:
g N2 = 0.400 moles N2 x = 11.2 g N2
MOLE-TO-MASS CONVERSIONS
28.0 g N2
1 mol N2

10. Calculate the mass, in grams of (a) 0.0728 mol silicon,
(b) 55.5 mol H2O, and (c) 0.0728 mol Ca(H2PO4)2
PRACTICE:

11. Find the formula mass of the following compounds:
1. C6H12O6 6. AlPO4
2. (NH2Cl)3MnO4 7. ZnCO3
3. NH4 8. KOH
4. F2 9. Al2(SO4)3
5. H2O2 10. [(Fe2O3)(SO2)]
SEATWORK:

12. Calculate the mass of SO2 that could be produced
from 2.50 moles O2. (5 points)
SEATWORK:

13. Conversion of Number of Atoms to
Moles
Mole= Avogadro’s number
Number of atoms__
Example:
How many moles are 2.80 x 1024 atoms of silicon?
Mol= 2.80 x 10 24 atoms
6.02 x 1023 atoms/mole
= 4.65 moles Si
Practice:
Find the number of moles in 5.12 x 1024 atoms of Mercury?

14. Conversion of number of moles to
atoms
Example: How many atoms are 0.360 moles of
Aluminum?
No. of atoms = mole x Avogadro’s number
= 0.360 mole x 6.02 x 1023 atoms/mole
= 2.17 x 1023 atoms Al

15. Conversion of Moles to Number of
Molecules
Example: How many molecules are 5.0 moles of
table sugar?
No. of molecules = mole x Avogadro’s number
= 5.0 moles x 6.02 x 1023 molecules/mol
= 3.01 x 1024 molecules sugar

16. Example: How many moles are there in 4.65 x
1024 molecules of CO2?
Mol =
Conversion of Molecules to Number
of Moles
4.65 x 1024 molecules
6.02 x 1023 molecules/mol
= 7.72 mol CO2

17. Conversion of moles to grams
Sample problem:
How many grams are in 2.5 moles of Calcium sulfide?
Solution: Calculate the formula mass of compound.
First step:
Ca = 1 x 40 g = 40 g
S = 1 x 32 g = 32 g
72g/mol
Second step:
2.5 mol CaS x
72 g CaS
1 mole CaS
= 180 g CaS

18. Percentage Composition
% mass of x =
____grams of x____
grams of compound X 100%

19. Percentage Composition
Sample problem: Calculate the percentage composition
of Aluminum hydroxide, a gastric antacid. The
formula is Al(OH)3 and the formula mass is 78 g.
% Al =
___Al__
Al (OH) 3
___27__
78g
= X 100 = 34.62%
% O
___O__
Al (OH) 3
= =
=
__48__
78g
X 100 = 61.54 %
% H
___H__
Al (OH) 3
= __3__
78g
X 100 = 3.85 %