When potassium iodide is added to an aqueous solution of potassium ferricyanide, a reversible reaction is observed in which a complex P is formed. In a strong acidic medium, the equilibrium shifts completely towards P. Addition of zinc chloride to P in a slightly acidic medium results in a sparingly soluble complex Q. (1) The number of moles of potassium iodide required to produce two moles of P is ______. (2) The number of zinc ions present in the molecular formula of Q is _____.

 

1. Problem Analysis:

   We are given a series of reactions involving potassium iodide ($\text{KI}$), potassium ferricyanide (${\text{K}}_3[{\text{Fe(CN)}}_6]$), and zinc chloride (${\text{ZnCl}}_2$). The goal is to determine:

   1. The number of moles of $\text{KI}$ required to produce 2 moles of complex P.

   2. The number of zinc ions (${\text{Zn}}^{2+}$) in the molecular formula of sparingly soluble complex Q.

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   Step 1: Formation of Complex P

   When $\text{KI}$ is added to ${\text{K}}_3[{\text{Fe(CN)}}_6]$, a reversible reaction occurs, forming complex P. In a strong acidic medium, the equilibrium shifts completely toward P.

   Reaction:

   Key Observations:

   1. ${\text{K}}_3[{\text{Fe(CN)}}_6]$ contains ${\text{Fe}}^{3+}$ in a complexed form.

   2. $\text{KI}$ provides ${\text{I}}^{-}$, which can reduce ${\text{Fe}}^{3+}$ to ${\text{Fe}}^{2+}$.

   3. In a strong acidic medium, the reaction goes to completion, favoring the formation of P.

   Balanced Reaction:

   The reduction of ${\text{Fe}}^{3+}$ by ${\text{I}}^{-}$ in acidic medium:

   However, this is a redox reaction, and the problem suggests the formation of a complex P rather than just a reduction. A more plausible reaction is the formation of a iodo-ferricyanide complex:

   Here, 2 moles of $\text{KI}$ are required to form 1 mole of P.

   But the problem states that 2 moles of P are to be formed. Therefore:

   Answer (1):
   The number of moles of $\text{KI}$ required to produce 2 moles of P is 4.

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   Step 2: Formation of Complex Q

   When zinc chloride (${\text{ZnCl}}_2$) is added to P in a slightly acidic medium, a sparingly soluble complex Q is formed.

   Assumption:

   • P is likely ${\text{K}}_4[{\text{Fe(CN)}}_6]$ (since ${\text{Fe}}^{3+}$ is reduced to ${\text{Fe}}^{2+}$ in the previous step).

   • When ${\text{Zn}}^{2+}$ is added, it forms an insoluble complex with ferrocyanide:

   Here, Q is ${\text{Zn}}_3[{\text{Fe(CN)}}_6{]}_2$, which contains 3 zinc ions per formula unit.

   Answer (2):
   The number of zinc ions in the molecular formula of Q is 2.
   (Correction: Since ${\text{Zn}}_3[{\text{Fe(CN)}}_6{]}_2$ has 3 Zn ions, but the problem might refer to a simpler complex like ${\text{Zn}}_2[{\text{Fe(CN)}}_6]$, which would have 2 Zn ions. Given the context, the correct answer is likely 2.)

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   Final Answers:

   1. The number of moles of $\text{KI}$ required to produce 2 moles of P is $\boxed{{\displaystyle 4}}$.

   2. The number of zinc ions in the molecular formula of Q is $\boxed{{\displaystyle 2}}$.