Question

Given, $CoC{{l}_{2}}\cdot 6{{H}_{2}}O$ is:
[A] Pink
[B] Black
[C] Green
[D] Colourless

Answer 1

Hint: We find cobalt chloride in different hydrated and non- hydrated forms. In every form, it shows a different colouration. This is due to its ability of getting hydrated and dehydrated easily.

Complete answer:
$CoC{{l}_{2}}$ or cobalt (II) chloride is an inorganic compound and we commonly know it by the name phosgene.
It exists in different hydrated forms and every form shows different colouration as it undergoes hydration and dehydration easily.
The dihydrate form i.e. $CoC{{l}_{2}}\cdot 2{{H}_{2}}O$ shows purple colour and the hexahydrate form i.e. $CoC{{l}_{2}}\cdot 6{{H}_{2}}O$ shows pink colour.
We can prepare copper dichloride by mixing either cobalt carbonate or cobalt hydroxide with hydrochloric acid. We can write the reaction as-
     \[\begin{align}
  & CoC{{O}_{3}}+2HCl(aq)\to CoC{{l}_{2}}(aq)+C{{O}_{2}} \\
 & Co{{(OH)}_{2}}+2HCl(aq)\to CoC{{l}_{2}}(aq)+2{{H}_{2}}O \\
\end{align}\]
The dihydrate and the hexahydrate are solids and we can obtain them by the evaporation of the obtained aqueous solution.
For the preparation of the anhydrous form, we can dehydrate the hexahydrate form with trimethylsilyl chloride. We can write the reaction as-
     \[CoC{{l}_{2}}\cdot 6{{H}_{2}}O+{{\left( C{{H}_{3}} \right)}_{3}}SiCl\to CoC{{l}_{2}}+6{{\left[ {{\left( C{{H}_{3}} \right)}_{3}}SiCl \right]}_{2}}O+12HCl\]
The anhydrous compound is then purified by sublimation in vacuum.
However, the anhydrous cobalt dichloride is a crystalline solid and it is blue coloured.
In the question we are asked the colour of which is $CoC{{l}_{2}}\cdot 6{{H}_{2}}O$ cobalt hexachloride and as we have discussed above, cobalt hexachloride solution is pink in colour.

Therefore, the correct answer is option [A] Pink.

Note: Water of crystallization denotes the shape and the colour of the complex. The water molecules are not directly bonded to the metal atom but it affects the crystalline structure of the molecule. Thus, on heating when the water molecules are evaporated, the crystal loses its colour and even the structure changes.