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Zorluk: Çok zorElectrochemical Series and Reaction Spontaneity
The standard reduction potentials for three half-cells are given below:
Cr3+(aq)+3e−→Cr(s)E∘=−0.74 V\text{Cr}^{3+}(aq) + 3e^- \rightarrow \text{Cr}(s) \quad E^\circ = -0.74\text{ V}
Fe2+(aq)+2e−→Fe(s)E∘=−0.44 V\text{Fe}^{2+}(aq) + 2e^- \rightarrow \text{Fe}(s) \quad E^\circ = -0.44\text{ V}
Ag+(aq)+e−→Ag(s)E∘=+0.80 V\text{Ag}^+(aq) + e^- \rightarrow \text{Ag}(s) \quad E^\circ = +0.80\text{ V}

A chemistry student intends to store an aqueous solution of iron(II) tetraoxonitrate(V), Fe(NO3)2\text{Fe(NO}_3)_2, in metal containers. Based on standard electrode potentials, which container choice is suitable for safely storing the solution without undergoing a spontaneous redox reaction?

  1. Only the Silver containerCevap
  2. B
    Only the Chromium container
  3. C
    Both the Chromium and Silver containers
  4. D
    Neither container

Cevap

Only the Silver container can safely store the iron(II) tetraoxonitrate(V) solution.
A redox reaction is spontaneous if the standard cell potential is positive (E°cell > 0). When storing aqueous iron(II) ions in a Silver container, the potential reaction involves oxidation of Silver metal and reduction of iron(II) ions: E°cell = E°(reduction) - E°(oxidation) = -0.44 V - (+0.80 V) = -1.24 V. Because E°cell is negative, the reaction cannot occur spontaneously, making the Silver container suitable. Conversely, for Chromium, E°cell = -0.44 V - (-0.74 V) = +0.30 V, which is positive and causes a spontaneous reaction that destroys the Chromium container.

Adım Adım Çözüm

1
Determine the cell potential E°cell for storing iron(II) solution in a Chromium container.
E°cell = E°cathode - E°anode = E°(Fe²⁺/Fe) - E°(Cr³⁺/Cr) = -0.44 V - (-0.74 V) = +0.30 V.
Chromium acts as the anode (oxidation) and iron(II) as the cathode (reduction).
2
Evaluate spontaneity for the Chromium container reaction.
Since E°cell = +0.30 V > 0, the reaction is spontaneous.
A positive standard cell potential indicates a feasible redox reaction, meaning the Chromium container will dissolve and react with the solution.
3
Determine the cell potential E°cell for storing iron(II) solution in a Silver container.
E°cell = E°(Fe²⁺/Fe) - E°(Ag⁺/Ag) = -0.44 V - (+0.80 V) = -1.24 V.
Silver acts as the anode (oxidation) and iron(II) as the cathode (reduction).
4
Evaluate spontaneity for the Silver container reaction and conclude safe storage.
Since E°cell = -1.24 V < 0, the reaction is non-spontaneous, so the Silver container safely holds the solution.
A negative cell potential means no spontaneous reaction occurs between Silver metal and aqueous iron(II) ions.

Anahtar Kavram

Spontaneity of Redox Reactions and Standard Cell Potential
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Konular

Electrochemical Series and Reaction Spontaneity

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