Masking and demasking reagents

  • Masking and demasking are techniques used to selectively protect or reveal certain ions or functional groups during chemical reactions or analysis.
  • These techniques are particularly useful in complex mixtures to control the reactivity of specific components and prevent unwanted side reactions.

1. Masking :

  • Masking involves temporarily protecting a specific ion or group by forming a stable, less reactive complex with a masking agent.
  • This allows selective reactions to occur without interference from the masked species.
  • Example: In complexometric titrations, a masking agent can bind certain metal ions, preventing them from reacting with the titrant while allowing other ions to be titrated.
Advertisements

2. Demasking:

  • Demasking is the reverse process where the masked ion or group is released by altering conditions (e.g., pH) or adding a demasking agent.
  • Example: After completing the titration of unmasked ions, demasking agents can be added to release the previously masked ions, allowing them to be titrated separately.

Masking and Demasking Reagents

  • Common Masking Reagents:

    • Ethylenediaminetetraacetic acid (EDTA): Masks many metal ions by forming stable complexes.
    • Cyanide ions (CN): Masks metals like silver (Ag⁺) and copper (Cu²⁺) by forming cyanide complexes.
    • Dimethylglyoxime (DMG): Masks nickel (Ni²⁺) by forming a stable red complex.
    • 1,10-Phenanthroline: Masks iron (Fe²⁺) by forming a stable complex.
  • Common Demasking Reagents:

    • Hydrogen peroxide (H₂O₂): Demasks chromium (Cr³⁺) from its EDTA complex by oxidation.
    • Oxalic acid: Demasks calcium (Ca²⁺) from fluoride by forming calcium oxalate.
    • Ammonium hydroxide (NH₄OH): Demasks aluminium (Al³⁺) and iron (Fe³⁺) from fluoride complexes by raising the pH.
    • Ascorbic acid: Demasks copper (Cu²⁺) by reducing it to Cu⁺, releasing it from cyanide complexes.
Advertisements
Advertisements

Thank you for reading from Firsthope's notes, don't forget to check YouTube videos!

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.