Lecture 4-Chemical Substances and Mole concept
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Moles and Atoms
Molar Mass for Compounds
) + O2(
) 2 H2O(
2 molecules H2(
) + 1 molecule O2(
) 2 molecules H2O(
2 moles H2(
) + 1 mole O2(
) 2 moles H2O(
This relationship can be made because of Avogadro’s number (NA)
Calculate the number of atoms found in 4.50 moles of silicon.
How many moles of silicon are in 2.45 x 1045 atoms?
The molar mass (μ)
of a substance is the mass per mole of its entities (atoms,
or formula units
Its unit is:
the mass of one
mole of a substance in grams
Carbon = 12.0 grams/mole
Sodium = 22.9 grams/mole
Molar mass (μ) of O2 = 2 ×μ of O = 2 ×16 = 32
What is molar mass for each of the following?
Copper metal =
Helium gas =
Calcium metal =
of a compound is the sum of the molar masses of the atoms of the elements in the formula.
Molar mass is the mass of one mole per single element while atomic mass is the mass of an atom at rest or is the number of protons and neutrons.
Molar mass is measured in grams per mole while atomic mass is “unitless.
What is the relationship between molar mass and atomic mass?
Mass for Compounds
Calculate the molar mass for water (H2O )?
H 2 x 1.01 g/mol = 2.02
O 1 x 16.00 g/mol =
Molar mass = 18.02 g/mol
Calculate the molar mass for each of the following:
Carbon dioxide (CO2)
Oxygen gas (O2)
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