Chapter 12: EDTA Titration

What is the purpose of an auxiliary complexing agent?

to weakly blind to a metal, preventing the metal hydroxide from precipitating in a basic solution during EDTA titration

what is necessary to perform an EDTA back titration instead of a direct titration?

1. analyte precipitates in the absence of EDTA

2. analyte reacts too slowyl with EDTA

3. analyte blocks the indicator

what pH range should the solution be buffered to if xylenol orange is used as the indicator?

pH 5-6

what color change will be observed at the end point for xylenol orange?

yellow to red

direct titration

you add the titrant (unknown solution) directly to the analyte (unknown solution) until the reaction is complete

• example; titrating HCl with NaOH

back titration

add an excess of standard reagent to the analyte, then titrate the left over reagent with another standard solution

indirect titration

you don’t titrate the substance itself; instead, you titrate another compound formed in a related reaction; anions that precipitate with certain metal cations can be analyzed with EDTA by indirect tiration

displacement titration

the analyte displaces another ion from a compound, and the displaced ion is then titrated. used in the absence of satisfactory indicator for specific metal ion, such as Hg2+