Transcript Relating Mass to numbers of atoms

RELATING MASS TO
NUMBERS OF ATOMS
The Mole, Avogadro’s Number, and Molar Mass
The Mole
■ The SI base unit used to measure the amount of a
substance.
■ It is the number of representative particles, carbon atoms,
in exactly 12 g of pure carbon-12.
■ A mole of anything contains 6.022 136 7 x 10 23
representative particles.
■ Note: A representative particle is any kind of particle such
as atoms, molecules, formula units, electrons, or ions.
Avogadro’s Number
■ Avogadro’s number, in honor of the Italian
physicist and lawyer Amedeo Avogadro
who, in 1811, determined the volume of
one mole of a gas.
■ 602 000 000 000 000 000 000 000
■ Round to three significant figures = 6.02 x
10 23
Converting: Moles to Particles &
Particles to Moles
Conversion Factors
1 mole
6.02 x 10 23 particles
6.02 x 10 23 representative particles
1 mole
How many particles of sucrose are in
3.5 moles of sucrose?
Number of moles x 6.02 x 10 23 representative particles
1 mole
3.5 moles x 6.02 x 10 23 particles
1 mole
= 2.11 x 10 24 particles of sucrose
Practice Problems
■ Determine the number of atoms in 2.5 mol. Zn.
■ Given 3.25 mol. AgNO3, determine the number of
formula units.
■ Calculate the number of molecules in 11.5 mol. H2O.
How many moles of Zinc contain 4.50 x
10 24 atoms of Zinc?
Number of representative particles
x
1 mole
6.02 x 10 23
4.50 x 10 24 atoms x 1 mole of Zinc
6.02 x 10 23 atoms
=7.48 mol. Zn
Practice Problems
How many moles contain each of the following:
a. 5.75 x 10 24 atoms Al
b. 3.75 x 10 24 molecules CO2
c. 3.58 x 10 23 formula units ZnCl2
d. 2.50 x 10 20 atoms Fe
Molar Mass
■ The molar mass of any element is numerically equal
to the atomic mass and has the units g/mol.
For example: An atom of manganese has an atomic
mass of 54.94 amu.
Therefore: the molar mass of manganese is 54.94
g/mol.
Converting: Moles to Mass & Mass to
Moles
Conversion Factors
Molar mass (g)
1 Mole
1 Mole
Molar mass (g)
How many grams of manganese are in
3.00 moles of manganese?
Number of moles x molar mass (g) =
1 mole
3.00 mol. of Mn. x 54,9 g of Mn. =
1 mol. Mn.
=165 g Mn
Practice Problems
Determine the mass in grams of each of the
following.
a. 3.57 mol Al
b. 42.6 mol Si
c. 3.45 mol Co
d. 2.45 mol Zn
How many moles of Calcium are in 525
g Calcium?
Mass (g) x 1 mole
=
Molar mass
525 g Ca x 1 mol Ca
40.08 g Ca
=13.1 mol Ca
Converting: Mass to Particles &
Particles to Mass
Step 1: Mass to Moles
Mass (g) x Molar mass
1 Mole
Step 2: Moles to Particles
23
Moles x 6.02 x 10 representative particles
1 mole
Molar Mass of Compounds
■ Water is composed of Hydrogen and Oxygen
■ H2O
■ WE HAVE: 2 H atoms
■ molar mass per H = 1 g … for 2 H = 2 g
WE HAVE :1 O atom molar mass per O = 16 g….
Therefore the molar mass for H2O = 2 g + 16 g = 18 g
Practice Problems
■ Find the molar mass for each of the following:
1. CO2
2. H2SO4
3. HCl
4. Ba(NO3)2
5. PbCl2