Counting particles: the mole
Atoms and molecules are far too small to count one by one, so chemists count them in moles. Put water, carbon, salt, carbon dioxide or glucose on a balance, change the mass, and find the moles and the number of particles.
Core concept
One mole of a substance is 6.022 × 10²³ particles (Avogadro's number), and its mass in grams equals the molar mass; so moles = mass ÷ molar mass, and particles = moles × 6.022 × 10²³
Topic: Atoms and molecules
A spoonful of water holds more molecules than there are grains of sand on many beaches, so chemists count particle: A tiny piece that matter is made of, far too small to see. All key words in big bundles called moles. One mole is 6.022 × 10²³ particles, Avogadro's number. The mass: How much matter something has, measured in grams or kilograms. It is the same everywhere. All key words of one mole in grams is the molar mass: add up the atomic masses in the formula. Water, H₂O, is 2 × 1 + 16 = 18 g/mol, so 18 g of water is one mole. To find moles, divide the mass by the molar mass; to find the particles, multiply the moles by 6.022 × 10²³.
What you will learn
- Find the molar mass of a substance from its formula.
- Calculate the number of moles in a given mass.
- Calculate the number of particles from the number of moles.
- Compare equal masses of different substances.
Before you start
- Know atomic masses and chemical formulae such as H₂O and CO₂.
Materials
- A kitchen balance, water, sugar and salt (to see what a mole looks like)
Equipment
- A calculator
Procedure
- Record 36 g of water.
- Record 18 g of water.
- Record 36 g of carbon.
- Record 90 g of glucose.
How this simulation is simplified
- Molar masses use whole atomic masses (H = 1, C = 12, O = 16, Na = 23, Cl = 35.5).