Topic 3 - Quantitative Chemistry

• Moles are used to compare quantities of substances
• Due to conservation of mass, the total mass of reactants must equal the total mass of products even if a gaseous product leaves
• Moles = 'Grams'/'RAMS' = mass (g)/relative atomic mass or formula mass
• 1 mole = 6.022 x 10^23 atoms
• 12g of carbon = 1 mole
• Relative formula mass (Mr)= sum of relative atomic masses of all the atoms in the formula
• Relative atomic mass (Ar) = Atomic number of the atom
• Stoichiometry: the ration of moles of one substance to another in a reaction
• In order for no reactants to be left over, there must be the correct number of moles of both reactants in order to react completely, according to their stoichiometry.
• When a substance is dissolved in water, it dissociates into its ions as the does the water (H+ and OH-)
• Concentration can be given in g/dm^3 or mol/dm^3
• cm^3 divided by 1000 = dm^3
• concentration (mol/dm^3) = moles/volume (dm^3)
• Percentage yield tells you what mass of product is made in a reaction in reality, compared to the maximum theoretical mass that could be made.
• Yield = (total mass of products/total mass of reactants) x 100
• Atom economy tells you how much of a desired product can be made in a reaction compared to the total mass of reactants (using RAMS)
• Atom economy = RAM of desired product/total RAM of reactants
• 1 mole of any gas takes up a volume of 24dm^3
• Moles of gas = volume (dm^3) divided by 24
• Volume = moles of gas x 24