Question

Give an example of the use of a masking agent

Short answer

The Mg²⁺ in a solution of Mg²⁺ and Fe³⁺ must be titrated by EDTA. If the Fe³⁺ is masked with to form $\mathrm{Fe}{\left(\mathrm{CN}\right)}_6^{3-}$ which does not react with EDTA.

Step-by-step solution

Introduction

The main criteria of masking are to prevent interference of one species in the analysis of another. This phenomenon is not restricted to EDTA titrations.

Masking agent

A masking agent is a type of reagent. It helps to protect the components of analyte from reaction with EDTA. Cyanide masks Cd²⁺, Zn²⁺, Hg²⁺, Co²⁺, Cu²⁺, Ag²⁺, Ni²⁺, Pd²⁺, Pt²⁺, Fe²⁺, and Fe²⁺, but not Mg²⁺, Ca²⁺, Mn²⁺, or Pb²⁺. When cyanide is added to a solution containing Cd²⁺ and Pb²⁺, only Pb²⁺ reacts with EDTA.

Example

The Mg²⁺ in a solution of Mg²⁺ and Fe³⁺ must be titrated by EDTA. If the Fe³⁺ is masked with ${\mathrm{CN}}^{-}$to form$Fe(CN{)}_6^{3-}$ which does not react with EDTA.