Topic 5 - Formulae, Equations and Amounts of Substances

the number of atoms found in exactly 12g of carbon-12 -unit for amount of substance

the number of particles in one mole 6.02 x10^23

the mass per mole of something this is the same as relative molecular mass Mr

Mr x no.moles

concentration x volume

mass/volume

mols x 6.023x10^23 (Avogadro’s constant)

the smallest whole number ratio of atoms of each element in a compound

the formula that shows the actual number of atoms of each type in a molecule

• calc mols of each element (mass/Mr) - divide by lowest no. mols (to get simplest ratio)

Ar of element x no.atoms in formula ____________________________ x100 Mr

• add acid drop by drop • swirl conical flask • rinse sides of flask with distilled water between additions • use white tile • compare colour of end point with previous titrations • rinse end of jet of burette with distilled water

to avoid overshooting the end point (ensure not too much acid was added)

to ensure all the acid and alkali react (create a homogeneous mixture)

to rinse all the reactants into the solution so they can all react

so the end-point can clearly be seen

to ensure consistency of the end point

to ensure all the acid is in the conical flask

obtained mass _____________ x100 theoretical mass

• incomplete rxn • loss in transfer • impurities formed • reversible rxn • incorrect measurements

pV = nRT

Pa

m3

÷1000000