Consider the following half-reactions: IrCl6^3-+3 e^-⟶Ir+6 Cl^- ℰ^∘=0.77 V PtCl4^2-+

Consider the following half-reactions: IrCl6^3-+3...

Consider the following half-reactions: $$\begin{array}{cc}\mathrm{IrCl}_{6}{ }^{3-}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Ir}+6 \mathrm{Cl}^{-} & \mathscr{E}^{\circ}=0.77 \mathrm{~V} \\ \mathrm{PtCl}_{4}{ }^{2-}+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pt}+4 \mathrm{Cl}^{-} & \mathscr{E}^{\circ}=0.73 \mathrm{~V} \\ \mathrm{PdCl}_{4}{ }^{2-}+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pd}+4 \mathrm{Cl}^{-} & \mathscr{E}^{\circ}=0.62 \mathrm{~V} \end{array}$$ A hydrochloric acid solution contains platinum, palladium, and iridium as chloro-complex ions. The solution is a constant $1.0 \mathrm{M}$ in chloride ion and $0.020 \mathrm{M}$ in each complex ion. Is it feasible to separate the three metals from this solution by electrolysis? (Assume that $99 \%$ of a metal must be plated out before another metal begins to plate out.)

Consider the following half-reactions:
$$\begin{array}{cc}\mathrm{IrCl}_{6}{ }^{3-}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Ir}+6 \mathrm{Cl}^{-} & \mathscr{E}^{\circ}=0.77 \mathrm{~V} \\
\mathrm{PtCl}_{4}{ }^{2-}+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pt}+4 \mathrm{Cl}^{-} & \mathscr{E}^{\circ}=0.73 \mathrm{~V} \\
\mathrm{PdCl}_{4}{ }^{2-}+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pd}+4 \mathrm{Cl}^{-} & \mathscr{E}^{\circ}=0.62 \mathrm{~V}
\end{array}$$
A hydrochloric acid solution contains platinum, palladium, and iridium as chloro-complex ions. The solution is a constant $1.0 \mathrm{M}$ in chloride ion and $0.020 \mathrm{M}$ in each complex ion. Is it feasible to separate the three metals from this solution by electrolysis? (Assume that $99 \%$ of a metal must be plated out before another metal begins to plate out.)

Key Concepts

Deposition Thresholds and Overpotential

Given criteria such as needing to plate out 99% of a metal before another begins deposition, it is important to consider not just the thermodynamics (reduction potentials) but also the kinetics and overpotentials involved. These factors together determine the feasibility of achieving high purity separation during the electrolysis process.

Selective Electrodeposition

Selective electrodeposition is based on exploiting differences in reduction potentials to deposit one metal preferentially over another. For separation by electrolysis, the potentials should be sufficiently separated so that the deposition of one metal can occur almost exclusively before the next metal starts to deposit.

Electroplating

Electroplating is the process of depositing a metal onto the surface of an electrode by passing electric current through a solution containing the metal ions. Understanding this process involves knowing how electrons reduce metal ions at the cathode to form a solid metal layer.

Nernst Equation

The Nernst equation helps adjust the standard reduction potentials for the actual concentration of the reactants and products in the half-cell reactions. It is essential to determining the actual electrode potential when the system is not under standard conditions, which is crucial in processes involving constant concentrations of certain ions.

Standard Reduction Potentials

This concept refers to the intrinsic tendency of different chemical species to be reduced, measured under standard conditions. In electrochemistry, the standard reduction potential indicates how readily a metal ion gains electrons to form the metal, which in turn affects the order in which metals can be deposited during electrolysis.

Transcript

00:02 Okay, this is a fairly complicated problem that requires several calculations.

00:07 In order for us to know whether or not we can plate these metals out and separate them to the 99 % level, then we need to figure out what the 99 % level is in terms of concentration.

00:20 So if we're going to play it out 99%, then there's only going to be 1 % left over.

00:25 So if we're starting with a .02 molar solution and 1 % is left, we're going to end up with a .0002 molar solution.

00:36 So what we have to do then is we need to figure out the electric potentials required for plating to begin for all of the metals from the metal complex at the .02.

00:56 Molar concentration.

00:58 Then we need to figure out what the potential will be required to plate out 99 % of the metal from the middle complex for each of them and see if those potential ranges overlap.

01:19 So for example, let's figure out what the electric potential is required to end the plating of iridium at 99 % plated.

01:34 So we'll use the nernst equation e equals the e standard given to us minus 0 .05916 divided by the three electrons log of the chloride concentration is given to us at one molar.

01:47 The stoichiometry requires us to take it to the sixth power and then the concentration that is desired when we have plated out 99 % is going to be 0 .0002.

02:00 This then gives us a voltage of 6 .97 volts.

02:05 Let's do the same thing and figure out the voltage required for aridium to begin plating...

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