Question

what are the differences and similarities between the back titrations and the displacement methods used in EDTA titrations. [6]

Answer 1

Back Titrations:

=> A known excess of EDTA is added to analyte

=> Free EDTA left over after all metal ion is bound with EDTA

=> The remaining excess of EDTA is then titrated with a standard solution of a second metal ion

=> Approach necessary if analyte: precipitates in the presence of EDTA, Reacts slowly with EDTA, Blocks the indicator.

=> Second metal ion must not displace analyte from EDTA

Displacement Titrations:

=> For metal ions that do not have a good indicator a second titration method is the displacement titration.

=> Here the analyte is treated with an excess of a second metal bound to EDTA.

=> The analyte ion displaces the second metal from the EDTA complex, and then the second metal is titrated with EDTA.

=> A typical displacement titration involves Hg as the analyte and MgEDTA at the displacement titrant.