2.1.3 Amount of substance

• a quantity to count number of particles in substance • measured in unit called mole (mol)

• the unit for amount of substance • 1 mole is the amount of substance that contains 6.02 x 10*23 particles

• N • the number of particles per mole • 6.02 x 10*23

• M • links moles with mass > it’s the mass per mole of a substance • units are gmol-1

moles = mass / mr - mr = mass / moles

• the volume per mole of a gas • units are dm3mol-1 • at room temp + pressure the vol is approx 24.9 dm3mol-1

volume (dm3) = amount of gas (moles) x 24

• the simplest whole number ratio of atoms of each element present in a compound

• divide the amount (g) of each element by molar mass - gives you molar ratio • divide the answer of each element by smallest number

• the number and type of atoms of each element in a molecule

• you would divide the relative molecular / formula mass (given) by the empirical formula mass (total mr) to give the number of units of that compound in a molecule • you would multiply that number by the compound to get the molecular formula

• anhydrous = without water • hydrated = with water

• many crystals are hydrated meaning they contain water molecules as part of their crystalline structure • the water is known as the water of crystallisation

• salt crystals containing waters of crystallisation

• a specific number

• how accurate is an experimental formula / how pure is it • all the water has been evaporated • no further decomposition

• concentration = moles / volume

• multiply your concentration by your mr to get gdm-3

• ‘M’ means molar and refers to a solution with a concentration in moles per cubic decimeter moldm-3 • example: 2 moldm-3 = 2M

pV = nRT - p = pressure (Pa) - V = volume (m3) - n = amount of gas molecules (mol) - R = ideal gas constant = 8.31 Jmol-1K-1 - T = temperature (K)

• maximum possible amount of product

• reaction may not have gone to completion • side reactions may occur, leading to by-products • reactants may may not be pure • some of reactants / products may be left behind in the apparatus • separation + purification may result in loss of some product

• percentage yield = (actual yield / theoretical yield) x 100

• a measure of how well atoms have been utilised > describes the efficiency of a reaction in terms of all atoms involved (takes into account all products including waste products)