KEY POINTS:

  • The mole is the unit of measurement in chemistry. It just so happens that one mole of a substance contains 6.02 x 1023 particles of that substance. It’s like a baker’s dozen, but a slightly larger number.
  • The mass of one mole of atoms is equal to the mass number of the element in question expressed in grams. So 1 mole of carbon atoms has a mass of 12g.
  • Balanced equations and chemical formulae tell us the mole ratios in which substances react and combine together. In CO2 there are two moles of oxygen atoms combined with one mole of carbon atoms, with a total mass of (12 + 16 + 16) = 44g. This number 44 is the formula mass of carbon dioxide.
  • For solids the following formula applies: MOLES = MASS (in g) / FORMULA MASS
  • For solutions this is extended to: CONCENTRATION = MOLES / VOLUME (in dm3)
  • And for gases at room temperature and pressure: MOLES = VOLUME (in dm3) / 24
  • N.B. 1 dm3 = 1,000 cm3

How Big is a Mole?

Stoichiometry: Chemistry for Massive Creatures

THINK OUTSIDE THE BOX:

  • Why is exact quantification so important in chemistry?
  • Find out more about the life of Avogadro. What was the evidence he used to support the mathematics involved?

Chemical Formulae & Equations

Return to the previous page.

Particles

Return to the beginning of the section.