In: Chemistry
uses and applications of maskig and demasking agents
In complexometric titration, whenever a solution contain more than one metal ions then to determine the concentration of each ion in solution we use masking and demasking agents. Masking agent prevent a metal ion to interfere in titration by forming complex with them. Demasking agent destroy the complex formed between metal ion and masking agent and make the metal ion free after which it participate in complexometric titration.
For example, if we have a solution containing Zn, Pb and Al then potassium cyanide is used to mask Zn, and excess disodium EDTA is used to mask Pb and Al. Excess EDTA is titrated with manganese sulphate using Eriochrome Black T as indicator. On adding Triethanolamine it demask Zn and after titration we get the concentration of Zn, on adding 2,3-dimercaptopropanol, Pb get demasked and we get the concentration of Pb, on adding formaldehyde-acetone mixture Al get demasked and we know the concentration of Al.
So, stepwise masking and demasking give us concentration of all ions present in solution.