T3 quantitative chemistry

no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants

RAM - average mass of atoms in an element taking into account masses and abundance of its isotopes RFM - sum of all RAM’s of all atoms in the formula

number of atoms, molecules or ions in a mole of a given substance 6.02x10^23

mass = Mr x moles

in a chemical reaction involving two reactants, common to use an excess of one of the reactants to ensure that all of the other reactant is used reactant that is completely used up is called the limiting reactant because it limits the amount of products

concentration (g per dm3) = mass(g) / volume(dm3) concentration (mol per dm3) = nr of moles / volume (dm3)

1 mole of a gas at room temperature and pressure occupies 24dm3

technique for finding the concentration of a solution by reacting a known volume of this solution with a solution of known concentration

• rinse the pipette with a solution of unknown concentration, use the pipette to measure out the known volume of this solution • add an indicator (substance that changes colour at the end ) • rinse the burette with a solution of known concentration, discard the liquid, use a burette to gradually add the solution of a known concentration • when indicator changes colour, volume added is recorded • important to get concordant volume results, have to lie close to each other • suitable calculations are performed to find the concentration

reaction may not go to completion because it’s reversible some of the product may be lost when it is separated from the reaction mixture some of the reactants may react in ways different to the expected reaction (side reactions may occur)

percentage yield = (actual yield / theoretical yield) x100

measure of the atom of starting materials that ends up as useful products ratio of the relative formula mass of desired product to the sum of relative formula masses of reactants

total Mr of desired product / total Mr of all reactants