3N: The Mole Concept

What is a mole?

To a biologist, a mole is an animal:

To a plastic surgeon, a mole is a bodily imperfection:

But to a chemist, a mole is a unit of measurement.

SI unit: mole
Symbol: mol
Definition: Amount of substance containing 6 x 10²³ particles

Why do we need this mole concept?

The mole concept enables us to calculate the amount of chemicals needed to make our clothing, food, drinks, toothpaste, medicine, printer inks and almost everything that has been manufactured.

What are the ways to measure a substance's mass?

There are three ways:

Relative atomic mass (A_r): 

• average mass of 1 atom compared to 1/12 of the mass of carbon-12 atom
• find directly from the Periodic Table
• no units

Relative molecular mass (M_r):

• average mass of 1 molecule compared to 1/12 of the mass of carbon-12 atom
• need to know chemical formula first, then sum up the A_r of all the atoms present in the compound
• no units

molar mass:

• mass of 1 mole of substance
• equivalent to A_r and M_r, but with units
• units: g/mol

What is the formula you need to know?

Have fun with the numbers!

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