UPSC Combined Geo-Scientist, Mains · 2020 · Mains Paper I

Q1(h). Masking and demasking

Question

Explain masking and demasking with reference to the complexometric titration.

Masking prevents an interfering metal from reacting with the titrant or indicator; demasking releases it for a subsequent determination.

A masking agent forms a sufficiently stable competing complex with the interfering ion, allowing another metal to be titrated selectively with EDTA.
For example, cyanide can mask Zn(II) through a cyanido complex while Ca(II)/Mg(II) are determined under suitable conditions.
Subsequent controlled reaction of cyanide with a reagent such as formaldehyde can release zinc for EDTA determination.

The full model answer

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CoversMaskingdemaskingSelective complexometry