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When concentrated HCl is added to an aqueous solution of CoCl2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?
  • a)
    [CoCl4]2–
  • b)
    [CoCl6]3–
  • c)
    [CoCl6]4–
  • d)
    [Co(H2O)6]2+
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
When concentrated HCl is added to an aqueous solution of CoCl2, its c...
Aqueous solution of CoCl2 contains [Co(H20)6]2+ which is pinkish in colour so option (d) is incorrect.
Reduction potential of Co3+ > Co2+ is high so option(b) is incorrect. Co2+ does not oxidize easily to Co3+.
It is a general case that symmetrical substituted octahedral complexes are less deeper in colour than tetrahedral complexes. So [CoCL]2- is deep blue in colour.
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Community Answer
When concentrated HCl is added to an aqueous solution of CoCl2, its c...
Complex Ion Responsible for Blue Colour:
When concentrated HCl is added to an aqueous solution of CoCl2, the reddish-pink color changes to deep blue due to the formation of the complex ion [CoCl4]2–.

Explanation:

Formation of the Complex Ion:
- When CoCl2 is dissolved in water, it forms Co2+ ions and Cl- ions.
- The addition of HCl causes the Cl- ions to coordinate with the Co2+ ions, forming a complex ion.
- The complex ion [CoCl4]2– is responsible for the deep blue color observed.

Color of the Complex Ion:
- The deep blue color of the [CoCl4]2– complex ion is due to the absorption of certain wavelengths of light by the complex.
- The absorbed light corresponds to the complementary color on the color wheel, which in this case is blue.

Conclusion:
- The [CoCl4]2– complex ion is responsible for the blue color observed when concentrated HCl is added to an aqueous solution of CoCl2.
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When concentrated HCl is added to an aqueous solution of CoCl2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?a)[CoCl4]2–b)[CoCl6]3–c)[CoCl6]4–d)[Co(H2O)6]2+Correct answer is option 'A'. Can you explain this answer?
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When concentrated HCl is added to an aqueous solution of CoCl2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?a)[CoCl4]2–b)[CoCl6]3–c)[CoCl6]4–d)[Co(H2O)6]2+Correct answer is option 'A'. Can you explain this answer? for NEET 2024 is part of NEET preparation. The Question and answers have been prepared according to the NEET exam syllabus. Information about When concentrated HCl is added to an aqueous solution of CoCl2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?a)[CoCl4]2–b)[CoCl6]3–c)[CoCl6]4–d)[Co(H2O)6]2+Correct answer is option 'A'. Can you explain this answer? covers all topics & solutions for NEET 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for When concentrated HCl is added to an aqueous solution of CoCl2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?a)[CoCl4]2–b)[CoCl6]3–c)[CoCl6]4–d)[Co(H2O)6]2+Correct answer is option 'A'. Can you explain this answer?.
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