Electrolysis when multiple ions present

In summary, the products of electrolysis of brine solution are hydrogen at the cathode and either chlorine or oxygen at the anode. The production of chlorine is due to the overpotential of oxygen, which means the electrode reaction for producing oxygen is slow and requires a higher potential. Concentration also plays a role in the products obtained, with dilute solutions producing oxygen and concentrated solutions producing SO4 2-. This is because in concentrated solutions, the transport of substances near the electrode can be disturbed, leading to the first available substance getting reduced/oxidized. The site and people involved in this conversation are considered to be helpful and knowledgeable.
  • #1
jd12345
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What are the products of electrolysis of brine solution?
At cathode i know it will be hydrogen

But i am confused about the products at anode:-
Either water will get oxidised or chlorine. Considering the oxidation potential values - water should get converted to oxygen but practically chlorine is obtained. My book says it is because of overpotential of oxygen( what does overpotential means?)

Also what has concentration related to the products obtained - example :- when electrolysis of sulphuric acid is done - water is oxidised to oxygen if solution is dilute and SO4 2- is oxidised to S2O82- if it is concentrated. Why?
Even if SO4 2- is available easily then also the most favoured reaction should proceed right? - which is oxidation of water
 
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  • #2
Potential of the reaction depends on the concentrations (see Nernst equation).

In concentrated solutions transport of the substance can be disturbed, which means there is not enough substance near the electrode, then the first thing present will get reduced/oxidized.

If the electrode reaction is slow, it doesn't go as expected on the electrode, even at its own redox potential. To speed it up we need to use higher potential - this is called overpotential. Trick is, if there is a competing fast reaction it may occur at some intermediate potentials before our main reaction gains speed. That's the case with water electrolysis, production of oxygen is notoriously slow.
 
  • #3
thank you - this site and people here are awesome...why didnt i find it earlier?
 

What is electrolysis?

Electrolysis is a process in which an electric current is used to drive a non-spontaneous chemical reaction. It involves the use of an external source of electricity to break down a compound into its constituent elements or ions.

How does electrolysis work?

During electrolysis, an electric current is passed through an electrolyte solution, which contains positively and negatively charged ions. The electric current causes the positively charged ions to move towards the negative electrode (cathode) and the negatively charged ions to move towards the positive electrode (anode). This movement of ions results in the separation of the compound into its constituent elements or ions.

What happens during electrolysis when multiple ions are present?

When multiple ions are present in the electrolyte solution, each ion will be attracted to the electrode with an opposite charge. For example, in a solution containing both sodium ions (Na+) and chloride ions (Cl-), the positively charged sodium ions will move towards the cathode and the negatively charged chloride ions will move towards the anode. This will result in the production of sodium metal at the cathode and chlorine gas at the anode.

What factors affect the rate of electrolysis?

The rate of electrolysis can be affected by several factors, including the concentration of ions in the electrolyte solution, the surface area of the electrodes, the strength of the electric current, and the type of electrodes used. Higher concentrations of ions, larger surface areas, stronger currents, and more reactive electrodes can all increase the rate of electrolysis.

What are some practical applications of electrolysis when multiple ions are present?

Electrolysis when multiple ions are present is used in a variety of industrial processes, such as the production of metals like aluminum and copper, the purification of metals, and the production of chlorine gas for use in water treatment. It is also commonly used in the production of batteries and fuel cells, as well as in the extraction of important compounds from natural resources. Additionally, electrolysis can be used in analytical chemistry to separate and identify different ions in a solution.

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