2.2 the mole and the avogadro constant Flashcards
What is a mole?
The mole is a way of measuring the amount of a substance in chemistry. It is commonly shortened to ‘mol’.
1 mole of any substance contains 6.02x1023…
atoms / molecules. For example, 1 mole of H2O contains 6.02x1023 molecules of H2O and 1 mole of Fe contains 6.02x1023 atoms of Fe.
We can calculate the number of particles in a substance using…
number of particles = Avogadro’s number x number of moles.
(Example) How many particles make up 0.67 moles of ammonia (NH3)?
Number of particles = 6.02x1023 x 0.67
number of particles = 4.03x1023
The number of moles can be calculated from mass and Mr/Ar.
Number of moles = mass (g) / Mr or Ar
(Example) Calculate the number of moles of 23g of gold. Give your answer to 2 significant figures.
Number of moles = mass / Ar
number of moles = 23 / 197
number of moles = 0.12mol (2 s.f)
The mole - solutions. The number of moles of a substance in a solution can be calculated from concentration and volume.
Number of moles = concentration (moldm-3) x volume (dm3)
(Example) Calculate the number of moles of 200cm3 of 0.35moldm-3 HCl.
Number of moles = concentration x volume
200cm3 must be in dm3: 200 / 1000 = 0.2 dm3
number of moles = 0.35 x 0.2 = 0.07moldm-3