Mole, Avogadro Constant & Molar Mass
Mole & Avogadro constant
- An amount of substance containing 6.02 × 1023 particles is called a mole (often abbreviated to mol).
- 6.02 × 1023 is called the Avogadro constant.
Example:
One mole of carbon contains 6.02 × 1023 of carbon atoms
One mole of oxygen contains 6.02 × 1023 of oxygen molecules
Molar mass
- The mass of one mole of a substance is called the molar mass.
- The molar mass of a substance is equal to its relative formula mass in grams.
Example:
What is the mass of 1 mole of carbon?
Solution:
The mass of 1 mole of carbon = relative formula mass of carbon = 12 grams
Example:
What is the molar mass of calcium carbonate (CaCO3)?
Solution:
Step 1: Look up the relative atomic masses of the atoms from the periodic table.
Relative atomic mass (rounded to the nearest whole number):
Ca = 40, C = 12, O = 16
Step 2: Calculate the relative formula mass.
Calcium carbonate (CaCO3) contains one calcium atom, one carbon atom and three oxygen atoms.
Relative formula mass = 40 + 12 + (3 × 16) = 100
Step 3: Express the relative formula mass in grams per mole.
The molar mass of ethanol is 100 g/mol
Example:
What is the molar mass of ethanol (C2H5OH)?
Solution:
Step 1: Look up the relative atomic masses of the atoms from the periodic table.
Relative atomic mass (rounded to the nearest whole number):
H = 1, C = 12, O = 16
Step 2: Calculate the relative formula mass.
Ethanol (C2H5OH) contains two carbon atoms, six hydrogen atoms and one oxygen atom.
Relative formula mass = (2 × 12) + (6 × 1) + 16 = 46
Step 3: Express the relative formula mass in grams per mole.
The molar mass of ethanol is 46 g/mol
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