These notes are an introduction to stoichiometry. we take a look at many different important concepts, such as molar mass, concentration and percentage yield and much more. I explain what these concepts are, how to calculate them and I have included examples as well
STOICHIOMETRY
Atomic Masses
The atomic masses are measured in atomic mass units (amu).
1 amu = 1.661 × 10-24g
Because atoms are too small to be expressed in gram
Example: 12C atom has an atomic mass of 12 amu.
Formula Weight: is the sum of all the atomic weights in a chemical formula. In
case of a molecule, it is known as molecular weight.
Atomic weight is the same as the atomic mass in the periodic table
The mole
Normally atoms are too small.
They group themselves for us to actually see them.
The mol: is the amount of substance that contain as many
elementary particles as there are atoms in exactly 12 g of 12C.
1 mole particle = 6.022 × 1023 particles (known as Avogadro’s number).
Particles can be molecules as well
1 mole particle = 6.022 × 1023 molecules. This is known as Avogadro’s
number
Molar mass
Molar mass: is the mass in grams of 1 mole of a substance.
The units are gram per mole (g.mol-1 or g/mol).
Example 1: Calculate the molar mass of O atom
16
O atom weighs 16 amu or 16 u
Molar mass is 16 g or 16 g/mol
Example 2: Calculate the molar mass of H2SO4
Formula weight= 2× (AW of H) + (AW of S) + 4 × (AW of O)
= 2× 1 amu + 32.1 amu + 4 × 16.0 amu
= 98.1 amu
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