Still that electrochemistry question

In summary, the conversation discusses the use of a three-electrode system for electrochemical reactions and the deposition of MnO2 and metallic Cr. The deposition of MnO2 requires a positive potential, while metallic Cr can be deposited at a negative potential. The reason for this difference is not clear, as both reactions are non-spontaneous and require external electric energy. The conversation also mentions an arrow in the reaction, which is not relevant to the summary.
  • #1
angela2007
3
0
my question is in three electrode system: working electrode, Pt counter electrode, and Ag/AgCl reference electrode.
for example, Mn2+ + 2 H2O -MnO2 + 4 H+ + 2 e− ( −1.22 V), the deposition of Mno2 will be accomplished on postive potential. Cr3+ +3e- Cr ( −0.74 V), the depsotion of metallic Cr will be accomplished on negative potential.
I Know for both the half-reactions, they are non-spontaneous and need external electric energy. My point is why the deposition of Mno2 is not done in negative potential range since E is equal to -1.22 V.

I cannot put the arrow in the reaction. please ingore that.

Thank you!
 
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  • #2
Are you asking what the difference is between plating out a conductive metal vs. a metallic oxide?
 
  • #3


In a three electrode system, the working electrode, counter electrode, and reference electrode all play different roles in the electrochemical reaction. The working electrode is where the desired reaction takes place, while the counter electrode balances the charge and the reference electrode provides a stable reference potential. In the given example, the working electrode is where the deposition of MnO2 takes place and the reference electrode maintains a stable potential for the reaction.

The reason why the deposition of MnO2 does not occur in the negative potential range is because the reference electrode is set at a specific potential (Ag/AgCl reference electrode has a potential of +0.197V vs. the standard hydrogen electrode). This means that the working electrode needs to reach a potential of -0.023V in order for the reaction to occur. In other words, the external electric energy applied to the system needs to overcome the potential difference between the working electrode and the reference electrode.

As for the deposition of metallic Cr, it occurs at a negative potential because the reference electrode has a more positive potential compared to the standard hydrogen electrode. This means that the working electrode needs to reach a more negative potential in order for the reaction to occur.

In summary, the potential difference between the working electrode and the reference electrode plays a crucial role in determining the direction of the electrochemical reaction. It is important to carefully select the reference electrode to ensure the desired reaction takes place.
 

What is electrochemistry?

Electrochemistry is a branch of chemistry that studies the relationship between electricity and chemical reactions. It involves the conversion of chemical energy into electrical energy, and vice versa.

What is the difference between electrolysis and galvanic cells?

Electrolysis is a process in which electrical energy is used to drive a non-spontaneous chemical reaction, while galvanic cells use chemical reactions to produce electrical energy.

What are some common applications of electrochemistry?

Electrochemistry is used in various industries, including batteries, corrosion prevention, electroplating, and fuel cells. It is also used in analytical techniques such as chromatography and mass spectrometry.

How does the concentration of ions affect the rate of an electrochemical reaction?

The concentration of ions can affect the rate of an electrochemical reaction by altering the availability of reactant molecules at the electrode surface. Higher ion concentration can lead to a faster reaction rate, while lower ion concentration can slow down the reaction.

What is the Nernst equation and how is it used in electrochemistry?

The Nernst equation is a mathematical formula that relates the standard reduction potential, concentration of reactants and products, and temperature to the electromotive force of an electrochemical cell. It is used to calculate the cell potential of a reaction under non-standard conditions.

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