If you use an indicator in a titration, the end point is the position at which the indicator changes colour. This may not be the exact point where the reactants have completely reacted but simply shows that a particular pH change has occurred. eg phenolphthalein changes colour between 8.3 and 10. So if you use this to titrate an alkali and acid and were adding the alkali to the acid, it would turn pink somewhere between these two values. If the titration is NaOH/HCl, the actual neutralisation point = 7, so you would have to add a fraction more NaOH after neutralisation to get the change. This may be a fraction of a drop as pH change is very rapid at the end point. So end point is the point shown by an indicator.
Equivalence point is the actual point where the reaction has just been completed and refers to the stoichiometric quantities of reactants eg when 1 mole HCl is added to 1 mole of NaOH. There will be more than one equivalence point for polyprotic acids and bases with more than 1 x OH- ions. You can get the equivalence points via titrations using a pH meter or conductivity equipment. So equivalence point represents the end point representing accurately the point at which reactants have just competely reacted - no extra needs to be added to get the indicator to change
Mon, 2012-01-23 03:39