Question

Which of the following cations gives blood red colour with KCNS?
A.$N{i^{2 + }}$
B.$F{e^{2 + }}$
C.$F{e^{3 + }}$
D.None of the above

Answer 1

Hint: Potassium thiocyanate (KCNS) when in contact with solutions containing $F{e^{3 + }}$, the product of the reaction is a solution with a blood red colour, due to the formation of the thiohydantoin complex ion $\left( {Fe{{\left( {CNS} \right)}_3}} \right)$.

Complete step by step answer:
The solution containing $F{e^{3 + }}$ cations when reacts with potassium thiocyanate (KCNS) gives a blood red colour product because of the formation of the $\left( {Fe{{\left( {CNS} \right)}_3}} \right)$.
$F{e^{3 + }} + 3KCNS \to Fe{(CNS)_3} + 3{K^ + }$
Thus, it gives blood red colour with KCNS
Similarly, this reaction is used as a test for $F{e^{3 + }}$ in the laboratory.

Therefore, the correct answer is option (C).

Note: Potassium thiocyanate (KCNS) is a compound that contains potassium, sulphur, carbon, and nitrogen atoms. Its density is \[1.89\dfrac{g}{{c{m^3}}}\], its molecular mass is \[97.181\dfrac{g}{{mole}}\] and its boiling point is and melting point . It is formed by the fusion of sulphur with potassium cyanide, extraction with hot aqueous alcohol, evaporating and cooling. It is colourless and has transparent prismatic crystals that are hygroscopic. It is odourless but has a cooling saline taste.
It is occasionally used for moderately realistic blood effects in film and theatre in the diluted form. It can be painted onto a surface or kept as a colourless solution. It is also used in the pharmaceutical industry such as potassium thiocyanate is used as a raw material for chemotherapeutic drugs, antibiotics and thyroid medications. The chemical industry too uses this inorganic reagent to produce photographs and textiles and to manufacture herbicides, fungicides and pesticides.