(A) The pink colour of the aqueous solution is due to the presence of the octahedral complex $[Co(H_2O)_6]^{2+}$. Upon the addition of $HCl$,the chlor

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(A) The pink colour of the aqueous solution is due to the presence of the octahedral complex $[Co(H_2O)_6]^{2+}$. Upon the addition of $HCl$,the chloride ions $(Cl^-)$ act as ligands and displace the water molecules to form the tetrahedral complex $[CoCl_4]^{2-}$,which is blue in colour. The reaction is: $[Co(H_2O)_6]^{2+} (\text{pink}) + 4Cl^- \rightarrow [CoCl_4]^{2-} (\text{blue}) + 6H_2O$.

Class 12 Chemistry Coordination Compounds Complexes and complex stability

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$A$ pink coloured aqueous solution of $Co(NO_3)_2$ turns blue on the addition of $HCl$ gradually. This colour change happens due to the formation of

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A
$[CoCl_4]^{2-}$
B
$[CoCl_6]^{4-}$
C
$[Co(H_2O)_4Cl_2]$
D
$[Co(H_2O)_2Cl_4]^{2-}$

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Coordination Compounds

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$A$ pink coloured aqueous solution of $Co(NO_3)_2$ turns blue on the addition of $HCl$ gradually. This colour change happens due to the formation of

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Assertion : $Cu^{2+}$ and $Cd^{2+}$ are separated from each other by first adding $KCN$ solution and then passing $H_2S$ gas.Reason : $KCN$ reduces $Cu^{2+}$ to $Cu^{+}$ and forms a complex with it.

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Assertion : $Cu^{2+}$ and $Cd^{2+}$ are separated from each other by first adding $KCN$ solution and then passing $H_2S$ gas.
Reason : $KCN$ reduces $Cu^{2+}$ to $Cu^{+}$ and forms a complex with it.