2.1.3 amount of substance

• amount of substance: the quantity that has moles as its unit

  chemists use 'amount of substance' as a way of counting atoms
• mole: the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon 12 isotope
• avogadro's constant: the number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol-1)
• molar mass: the mass per mole of a substance. units = g mol -1
• molar gas volume: gas volume per mole, units dm^3 mol-1

  this is the volume of 1 mole of a gas at a given temperature, all gases have this same volume

  at room pressure (1 atm) and room temp 25 degrees celsius, the molar gas volume is 24 dm3 mol-1
• no. of moles (mol) = mass (g) / molar mass (g mol -1)
• empirical formula: the simplest ratio of atoms of each element in the compound
• molecular formula: the actual number of atoms of each element in the compound
• anhydrous: refers to a substance that contains no water molecules
• hydrated: refers to a crystalline compound containing water molecules
• water of crystallisation: refers to the water molecules that form an essential part of the crystalline structure of a compound