Question

Lab 9 - Qualitative Analysis of Cations One common compound that is used in detecting metal cations is ethylenediaminetetraacetic acid or simply EDTA. EDTA forms complexes with metals cations which effectively chelates them in solution. The EDTA- anion binds the metal cations which often result in a chelated metal-EDTA anion. For example, iron (III) will form the [Fe(EDTA)]- anion and would be highly soluble in water. With this information, would EDTA be useful in this lab for detecting the 9 metal cations from your known cation solution if they bind to EDTA anion in the same way as the iron example above? Explain why or why not

Answer 1

Ans:

Yes, the EDTA would be useful for detecting the metal ions. In principle, if EDTA can be chelated or complexed with the metal ions, they can be estimated by titration using suitable pH buffer and indicator. EDTA is a hexa-dentate chelator with four carboxylic acid and two amino nitrogens also as donors. This type of titrations are called is complexometric titration. The metal complexes are formed as per the below reaction:

Mn+ (metal ion) + Y4- (EDTA ion) → MY(n-4) (complexed ion)