Question

What will be the colour change, if $K_3\left[Fe\right(CN{)}_6]$ is used as an external indicator in the dichromate estimation of $F{e}^{2+}$?

• A. Colourless to blue
• B. Blue to red
• C. Colourless to red
• D. Blue to colureless

Answer 1

Answer: (D)

Blue to colureless

$F{e}^{2+}$ ions react with pottasium ferricyanide to form a blue precipitate of Turnbull's blue.
$F{e}^{2+}+\left[Fe\right(CN{)}_6{]}^{3-}\to Fe\left[Fe\right(CN{)}_6{]}^{-}$
Hence, the end point will be blue to colourless.