Copper ion forms blue coloured complex with ligand `NH_(3)` and a colourless complex with ligand. 'B' which has low dissociation constant than `Cu^(2+)` with `NH_(3)` . Conc. Of `Cu^(2+)` can be estimated by titration using `NH_(3)` and B is

Options

A. `NH_(3)` as a titrant and B as indicator
B. The end point with appearance of blue colour
C. Using 'B' as titrant and `NH_(3)` as indicator
D. The end point will correspond to first disappearance of colour

Answer

C,D

Explanation

`(C )` and `(D)` are correct.
`Cu^(2+)+4NH_(3)rarr [Cu(NH_(3))_(4)]^(2+)`
Blue colour will disappear when 'B' is added due to formation of colourless complex
a and b are not correct because complex is more stable with `NH_(3)` and Not with 'B'