Indicator that would give an end point for titration of the 1st 2 proton in h3aso4
Answers
Answered by
0
Titration of polyprotic acids (or bases) requires more attention than titration of monoprotic ones. There are two reasons for that.
First, polyprotic acid can have more then one inflection point on the titration curve. As in laboratory practice possible pH change during titration is limited to about 7-8 units at most, that means steep part of the titration curve - when split between two end points - must be short. As we have seen in the end point detection section it doesn't help to achieve good accuracy of titration.
Second, quite often without precise analysis it is not obvious what is stoichiometry of the reaction. For example, when we titrate phosphoric acid with strong base, we will be never able to observe third end point (titration curve is completely flat in this area). Thus we have to select indicator that will allow titration of either only first proton, or two protons - and calculate reaction stoichiometry aaccordingly. Even then determination won't be easy - see titration curve below.
First, polyprotic acid can have more then one inflection point on the titration curve. As in laboratory practice possible pH change during titration is limited to about 7-8 units at most, that means steep part of the titration curve - when split between two end points - must be short. As we have seen in the end point detection section it doesn't help to achieve good accuracy of titration.
Second, quite often without precise analysis it is not obvious what is stoichiometry of the reaction. For example, when we titrate phosphoric acid with strong base, we will be never able to observe third end point (titration curve is completely flat in this area). Thus we have to select indicator that will allow titration of either only first proton, or two protons - and calculate reaction stoichiometry aaccordingly. Even then determination won't be easy - see titration curve below.
Similar questions