D-And F-Block Elements Ques 493
Question: When concentrated $ HCl $ is added to an aqueous solution of $ CoCl_2 $ its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction-
Options:
A) $ {{[CoCl_4]}^{2-}} $
B) $ {{[CoCl_6]}^{3-}} $
C) $ {{[CoCl_6]}^{4-}} $
D) $ {{[Co{{(H_2O)}_6}]}^{2+}} $
Show Answer
Answer:
Correct Answer: A
Solution:
Aqueous of solution of $ CoCl_2 $ contains $ {{[Co{{(H_2O)}_6}]}^{2+}} $ which is pinkish in colour so option [d] is incorrect.
Reduction potential of $ C{{o}^{3+}}\xrightarrow{{}}C{{o}^{2+}} $ is high so option[b] is incorrect.
$ C{{o}^{2+}} $ does not oxidises easily to $ C{{o}^{3+}} $ .
It is general case that symmetrical substituted octahedral complexes are less deeper in colour than tetrahedral complexes.
So $ {{[CoCl_4]}^{2-}} $ is deep blue in colour.
