Why EDTA is used in back titration?

When the reaction is complete, excess EDTA is back titrated to the end point using a magnesium or zinc standard solution with eriochrome black T. This procedure is useful for determining cations that form stable complexes with EDTA and for which there is no effective indicator.

Why al EDTA direct titration is not possible?

Direct determination of aluminum with EDTA is impossible – complexation reaction is too slow, making titration impractical. If solution was prepared by dissolving sample containing Al in a strong acid, it may have very low pH.

What is the advantage of back titration?

A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with precipitation reactions. Back titrations are also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid.

How is back titration different than direct titration?

In a direct titration, you add a standard titrant to the analyte until you reach the end point. In a back titration, you add an excess of standard titrant to the analyte, and then you titrate the excess titrant to determine how much is in excess.

How is back titration used?

When are back-titrations used? Back titrations are mainly used in the following cases: if the analyte is volatile (e.g., NH3) or an insoluble salt (e.g., Li2CO3) if the reaction between analyte A and titrant T is too slow for a practical direct titration.

What is back titration of aspirin?

Aspirin is a weak acid that also undergoes slow hydrolysis; i.e., each aspirin molecule reacts with two hydroxide ions. To overcome this problem, a known excess amount of base is added to the sample solution and an HCl titration is carried out to determine the amount of unreacted base.

Why is it called a back titration?

Back titration is also titration. It is called back titration because it is not carried out with the solution whose concentration is required to be known (analyte) as in the case of normal or forward titration, but with the excess volume of reactant which has been left over after completing reaction with the analyte.