Q. A solution of sodium thiosulphate on addition of few drops of ferric chloride gives violet colour due to the formation of
A) $Na_{2}S_{4}O_{6}$
B) $Fe_{2}\left( SO_{4} \right)_{3}$
C) $Fe_{2}\left( S_{2}O_{3} \right)_{3}$
D) $Fe_{2}\left( S_{2}O_{3} \right)_{2}$
Explanation
(c)
When a few drops of $FeCl_{3}$ solution is added to hypo solution, a violet colour of ferric thiosulphate is obtained.
$3Na_{2}S_{2}O_{3} + 2FeCl_{3}\ \rightleftharpoons Fe_{2}\left( S_{2}O_{3} \right)_{3} + 6NaCl$
violet colour
This colour disappears quickly due to reduction of ferric chloride by thiosulphate.
$2FeCl_{3} + 2Na_{2}S_{2}O_{3}\ \rightarrow 2FeCl_{2} + Na_{2}S_{4}O_{6} + 2NaCl$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.