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Standard XII

Chemistry

Methods for Ester Synthesis

The overall f...

Question

The overall formation constant for the reaction of $6 m o l of -^{C} N i o n s$ with Co(II) ions is $10^{20}$ . The standard reduction potential for the reaction $[C o (C N)_{6}]^{3 -} + e^{-} \to [C o (C N)_{6}]^{4 -} is - 0.78 V$
$C o^{3 +} + e^{-} \to C o^{2 +} E^{\circ} = 1.80 V$
If the formation constant for $[C o (C N)_{6}]^{3 -} is 10 a$ , then the value of a is

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Solution

$(1) C o^{2 +} + 6 C N^{-} \to [C o (C N)_{6}]^{4 -} K_{f} = 10^{20}$
$(2) C o^{3 +} + e^{-} \to C o^{2 +} = E^{o} = 1.80 V$
$K c_{2} = 10^{30}$
$(3) [C o (C N)_{6}]^{3 -} + e^{-} \to [C o (C N)_{6}]^{4 -} E^{o} = - 0.78 V$
$K c_{3} = 10^{- 13}$
$(4) C o^{3 +} + 6 C N^{-} \to [C o (C N)_{6}]^{3 -} k_{f_{4}}$
$e q 1 + e q 2 - e q 3 = e q 4$
Formation constant
$k_{f_{4}} = \frac{k_{f} \times k_{c_{2}}}{k_{c_{3}}} = \frac{10^{20} \times 0^{30}}{10^{- 13}}$ .

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Q. The overall formation constant for the reaction of 6 mole of

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1 \times 10^{19}

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, if the ans can be expressed as

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Q. Question below refers to the overall reaction and half-reactions with standard reduction potentials below.

2 F e^{2 +} + C l_{2} \to 2 F e^{3 +} + 2 C l

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Q. In

[C o (C N)_{6}]^{4 -}

and

[C o (C N)_{6}]^{3 -}

The colour of the coordination compounds depends on the crystal field splitting. What will be the correct order of absorption of wavelength of light in the visible region, for the complexes, $[C o (N H_{3})_{6}]^{3 +}, [C o (C N)_{6}]^{3 -}, [C o (H_{2} O)_{6}]^{3 +}$
$[C o (N H_{3})_{6}]^{3 +}, [C o (C N)_{6}]^{3 -}, [C o (H_{2} O)_{6}]^{3 +}$
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(b) $[C o (N H_{3})_{6}]^{3 +} > [C o (H_{2} O)_{6}]^{3 +} > [C o (N H_{3})_{6}]^{3 +}$
(c) $[C o (H_{2} O)_{6}]^{3 +} > [C o (N H_{3})_{6}]^{3 +} > [C o (C N)_{6}]^{3 -}$
(d) $[C o (C N)_{6}]^{3 -} > [C o (N H_{3})_{6}]^{3 +} > [C o (H_{2} O)_{6}]^{3 +}$

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The overall formation constant for the reaction of 6molof–CNions with Co(II) ions is 1020. The standard reduction potential for the reaction [Co(CN)6]3–+e–→[Co(CN)6]4–is–0.78V Co3++e–→Co2+E∘=1.80V If the formation constant for [Co(CN)6]3–is10a, then the value of a is

(1)Co2++6CN–→[Co(CN)6]4–Kf=1020 (2)Co3++e–→Co2+=Eo=1.80V Kc2=1030 (3)[Co(CN)6]3–+e–→[Co(CN)6]4–Eo=–0.78V Kc3=10−13 (4)Co3++6CN–→[Co(CN)6]3–kf4 eq1+eq2–eq3=eq4 Formation constant kf4=kf×kc2kc3=1020×03010−13.