Electrolysis in Cu/Hg electrolytic cell

In summary, the conversation is discussing the process of electrolysis and specifically the ratio of moles of copper to moles of mercury deposited. The species involved in the process are Cu^{2 + } /SO_4 ^{2 - } ions, Hg_2 ^{2 + } /NO_3 ^ - ions, and H_2 O. The process involves Cu^{2 + } ions being reduced at the cathode and Hg_2 ^{2 + } ions being oxidized at the anode. The question about the ratio of copper to mercury produced is addressed by further electrolysis of Hg^{2 + } ions. The conversation ends with a request for clarification and an explanation of the rules to
  • #1
steven10137
118
0

Homework Statement



http://img143.imageshack.us/img143/7135/electrolysisrf2.jpg [Broken]

What is the ratio of number of moles of copper deposited to the number of moles of mercury deposited? {n(Cu):n(Hg)}

2. The attempt at a solution

Well the species present are;
[tex]
\begin{array}{l}
Cu^{2 + } /SO_4 ^{2 - } \;ions \\
Hg_2 ^{2 + } /NO_3 ^ - \;ions \\
and\;H_2 O \\
\end{array}
[/tex]

so reading down the Eo table from left to right; the first species found is [tex]Cu^{2 + }[/tex] ions.
So at the cathode we have; [tex]Cu^{2 + } + 2e^ - \to Cu[/tex]

Now reading up the Eo table from right to left; the first species found is [tex]Hg_2 ^{2 + }[/tex]
So I would assume that at the anode we have; [tex]Hg_2 ^{2 + } \to 2Hg^{2 + } + 2e^ - [/tex]

Now the question states that it is the ratio of copper to mercury produced. How can this be?
Do I just assume that the mercury ions are now further electrolysed to mercury by;
[tex]Hg^{2 + } + 2e^ - \to Hg_{(l)}[/tex]

Could someone please explain how this works and what rules I am supposed to be following as I am a little confused ...

cheers
Steven
 
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  • #2
Anybody

- sorry I have an exam Friday :(
 
  • #3

You are correct in your assumption that the ratio of copper to mercury produced is based on the electrolysis reactions at the cathode and anode. However, in this case, the mercury ions are not further electrolyzed to form liquid mercury. Instead, they are reduced to form solid mercury on the cathode. This is because the standard reduction potential for Hg^{2 + } to Hg_{(l)} is lower than that of Cu^{2 + } to Cu.

The overall reaction for the electrolysis of the Cu/Hg electrolytic cell is:

Cu^{2 + } + Hg_2 ^{2 + } \to Cu + 2Hg_{(s)}

Therefore, for every mole of Cu deposited at the cathode, 2 moles of Hg will also be deposited. This means that the ratio of n(Cu):n(Hg) is 1:2.

As for the rules you should follow, it is important to first identify the species present in the electrolytic cell and their corresponding reduction potentials. Then, use the reduction potentials to determine the reactions at the cathode and anode. Finally, combine these reactions to determine the overall reaction and the ratio of moles of each product formed.
 

What is electrolysis?

Electrolysis is a process that uses an electrical current to break down a compound into its constituent elements. It involves the use of an electrolytic cell, where a chemical reaction occurs at the electrodes due to the flow of electricity.

How does an electrolytic cell work?

An electrolytic cell consists of two electrodes, an anode and a cathode, immersed in an electrolyte solution. When a direct current is passed through the cell, the positive ions in the solution are attracted to the negative cathode and gain electrons, while the negative ions are attracted to the positive anode and lose electrons. This results in a chemical reaction at the electrodes, causing the electrolysis process to occur.

What is the purpose of using a Cu/Hg electrolytic cell?

A Cu/Hg electrolytic cell is used for refining copper metal. The copper is dissolved in the electrolyte solution and deposited onto the cathode, while the impurities settle at the bottom of the cell as a sludge. The mercury acts as a cathode, preventing the copper from re-dissolving back into the electrolyte solution.

What are the challenges of using a Cu/Hg electrolytic cell?

One challenge is the environmental impact of using mercury, which is toxic and can pose health hazards if not handled properly. Another challenge is the potential for contamination of the copper with mercury, which can affect its properties and make it unsuitable for certain applications.

How is the efficiency of a Cu/Hg electrolytic cell measured?

The efficiency of a Cu/Hg electrolytic cell is measured by the amount of electrical energy used to refine a certain amount of copper. This is known as the energy consumption per unit of copper produced, and it can vary depending on factors such as the purity of the copper and the type of electrolyte solution used.

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