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Coordination Compounds question

2023 · 25 Jan · Shift 2 · Q10
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Coordination Compounds question

2023 · 25 Jan · Shift 2 · Q10

JEE MainChemistryCoordination CompoundsMCQ+4 / −1

Match List I with List II

List I
Coordination entity		 List II
Wavelength of light absorbed in nm
A. [CoCl(NH3)5]2+\mathrm{[CoCl(NH_3)_5]^{2+}}[CoCl(NH3​)5​]2+ I. 310
B. [Co(NH3)6]3+\mathrm{[Co(NH_3)_6]^{3+}}[Co(NH3​)6​]3+ II. 475
C. [Co(CN)6]3−\mathrm{[Co(CN)_6]^{3-}}[Co(CN)6​]3− III. 535
D. [Cu(H2O)4]2+\mathrm{[Cu(H_2O)_4]^{2+}}[Cu(H2​O)4​]2+ IV. 600

Choose the correct answer from the options given below :

  1. A
    A-IV, B-I, C-III, D-II
  2. B
    A-III, B-II, C-I, D-IV
  3. C
    A-III, B-I, C-II, D-IV
  4. D
    A-II, B-III, C-IV, D-I
View written solutionFree

Correct answer: B

  1. Use crystal field splitting and spectrochemical series

    The wavelength absorbed is related to crystal field splitting by

    Δ=hcλ\Delta = \frac{hc}{\lambda}Δ=λhc​

    So, smaller wavelength means larger splitting.

    Spectrochemical strength:

    CN−>NH3>H2O>Cl−\mathrm{CN^- > NH_3 > H_2O > Cl^-}CN−>NH3​>H2​O>Cl−

  2. Analyze each complex

    (C) [Co(CN)6]3−\mathrm{[Co(CN)_6]^{3-}}[Co(CN)6​]3−

    • Metal: Co3+\mathrm{Co^{3+}}Co3+
    • Ligand: CN−\mathrm{CN^-}CN− is very strong field
    • Hence it has the largest Δ\DeltaΔ
    • Therefore it absorbs smallest wavelength
    C→310 nm(I)C \to 310\,\text{nm} \quad (I)C→310nm(I)

    (B) [Co(NH3)6]3+\mathrm{[Co(NH_3)_6]^{3+}}[Co(NH3​)6​]3+

    • Metal: Co3+\mathrm{Co^{3+}}Co3+
    • Ligand: NH3\mathrm{NH_3}NH3​ strong field, but weaker than CN−\mathrm{CN^-}CN−
    • So splitting is less than (C), but still large
    • Hence next smaller wavelength
    B→475 nm(II)B \to 475\,\text{nm} \quad (II)B→475nm(II)

    (A) [CoCl(NH3)5]2+\mathrm{[CoCl(NH_3)_5]^{2+}}[CoCl(NH3​)5​]2+

    • Let oxidation state of Co be xxx: x+(−1)=+2⇒x=+3x + (-1) = +2 \Rightarrow x=+3x+(−1)=+2⇒x=+3
    • So metal is again Co3+\mathrm{Co^{3+}}Co3+, but one Cl−\mathrm{Cl^-}Cl− ligand is weak field
    • Therefore splitting is less than [Co(NH3)6]3+\mathrm{[Co(NH_3)_6]^{3+}}[Co(NH3​)6​]3+
    • So it absorbs longer wavelength than (B)
    A→535 nm(III)A \to 535\,\text{nm} \quad (III)A→535nm(III)

    (D) [Cu(H2O)4]2+\mathrm{[Cu(H_2O)_4]^{2+}}[Cu(H2​O)4​]2+

    • Metal: Cu2+\mathrm{Cu^{2+}}Cu2+
    • Ligand: H2O\mathrm{H_2O}H2​O is weaker field than NH3\mathrm{NH_3}NH3​
    • Also Cu2+\mathrm{Cu^{2+}}Cu2+ generally has smaller splitting than Co3+\mathrm{Co^{3+}}Co3+
    • Hence this has the smallest splitting among these
    • Therefore it absorbs the largest wavelength
    D→600 nm(IV)D \to 600\,\text{nm} \quad (IV)D→600nm(IV)

  3. Final matching

    A→III,B→II,C→I,D→IVA\to III,\quad B\to II,\quad C\to I,\quad D\to IVA→III,B→II,C→I,D→IV

  4. Compare with options

    This corresponds to Option B.

  5. Comparison with stored correct answer

    Stored correct answer = B

    Our derived answer = B

    Hence, they agree.

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