Question

Which of the following changes the colour of the aqueous solution of $FeC{l_3}$​?
(A) ${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$
(B) ${H_2}S$
(C) $N{H_4}CNS$
(D) $KCNS$

Answer 1

Hint: With the chemical formula $FeC{l_3}$ , ferric chloride is an inorganic substance with a wide range of applications in industry, medicine, and laboratories. Iron chloride is the name given to ferric chloride. It is a chemical substance with the molecular formula $FeC{l_3}$ . It changes its colour on reaction with all the 4 chemical compounds in the question.

Complete Step by Step Solution:
It is a solid that ranges in colour from orange to brown-black. It barely dissolves in water. It is inflammable. Most metals, including aluminium, are corroded by it when moist. Before adding water, pick up any spilled solid and remove it. It is employed in the production of other chemicals, the treatment of sewage and industrial waste, the purification of water, the etching of circuit boards, and the purification of water.

Iron has a +3 oxidation state in ferric chloride, a common combination of iron and chlorine. Iron(III) chloride or Iron trichloride are its IUPAC names. In addition to ferric chloride, it also goes by the names molysite and flores martis. It has many different colours, such as a black-green or purple appearance in its anhydrous form and a solid yellow appearance in its hydrous form.

Ferric chloride is dangerous, extremely corrosive, and naturally acidic. In exchange, the anhydrous substance is a potent dehydrating agent. Despite the rarity of human poisoning, consuming ferric chloride can cause substantial morbidity and raise the fatality rate.
Now we will see how ferric chloride reacts with each of the chemical compounds given in the question and the final colour of the product so formed.

 $FeC{l_3}$ on reaction with ${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$ forms $F{e_4}{\left[ {Fe{{\left( {CN} \right)}_6}} \right]_3}$ which is blue in colour.
 $FeC{l_3}$ when reacted with ${H_2}S$ gives $F{e_2}{S_3}\,\& \,HCl$ out of which $F{e_2}{S_3}$ is light yellow in colour.

Now when $FeC{l_3}$ reacts with $N{H_4}CNS$ we get$Fe{\left( {CNS} \right)_3}\,\& \,N{H_4}Cl$ where $Fe{\left( {CNS} \right)_3}$ is blood red in colour.
Similarly when $FeC{l_3}$ reacts with $KCNS$ , $Fe{\left( {CNS} \right)_{3\,}}\,\& \,KCl$ are formed out of which $Fe{\left( {CNS} \right)_3}$ is blood red in colour.
Thus, we see that all the 4 compounds change the colour of $FeC{l_3}$ .
Hence, option A., B., C., D. all are correct answers.

Note: We see that the colour of $FeC{l_3}$ is changed by all the compounds given in the question but we should know that these are not the only compounds that change the colour of $FeC{l_3}$ . There are many more chemical compounds that do so. Hence, same question with different options can also be given.