Mole
The amount of a substance that contains 6.02 x 10^23 particles. One mole of a substance weighs its relative formula mass in grams.
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Analogy
A mole is like a dozen, but for atoms. A dozen is 12 things. A mole is a huge fixed number of things.
Example
Carbon (C): 12 gWater (H2O): 18 gSodium chloride (NaCl): 58.5 g
In practice
One mole of carbon atoms weighs 12 g. One mole of water molecules weighs 18 g.
Practice
Flashcards
- What is the Avogadro constant?6.02 x 10^23, the number of particles in one mole.
Interview questions
- Calculate the mass of 0.5 mol of calcium carbonate, CaCO3. (Ar: Ca = 40, C = 12, O = 16)
- Mr = 40 + 12 + 3 x 16 = 100
- Mass = moles x Mr
- 0.5 x 100 = 50 g
Questions people ask
Why do chemists use moles?
Atoms are far too small to count one by one. The mole links a number of particles to a mass that can be weighed on a balance. The relative formula mass in grams is always one mole, so you can measure out exactly equal numbers of different particles.
How many atoms are in one mole of carbon?
One mole of carbon contains 6.02 x 10^23 atoms, and weighs 12 g. The same number of atoms is in one mole of any element. So 24 g of magnesium holds the same number of atoms as 12 g of carbon, even though magnesium atoms are heavier.