2.5.1. Products of Electrolysis

Products of electrolysis depend on the nature of material being electrolysed and the type of electrodes being used. If the electrode is inert (e.g., platinum or gold), it does not participate in the chemical reaction and acts only as source or sink for electrons. On the other hand, if the electrode is reactive, it participates in the electrode reaction.

During electrolysis, the products formed at the electrodes depend heavily on the electrodes’ nature and the substance being electrolyzed. Inert electrodes, which do not undergo any chemical change, only facilitate the reaction by allowing electrons to enter or exit the solution. Reactive electrodes, however, take part in chemical reactions, leading to different products being formed at the electrodes. For instance, if using a reactive copper electrode, copper ions may deposit on the electrode during electrolysis, unlike when using an inert electrode.

Think of an inert electrode like a traffic light that simply manages traffic flow without interfering with the cars. The cars represent the electric charges (electrons), and they can move in and out without the traffic light getting involved in their interaction. In contrast, a reactive electrode is akin to a traffic police officer who plays an active role in directing cars and may also be affected by their movements.

Thus, the products of electrolysis may be different for reactive and inert electrodes. The products of electrolysis depend on the different oxidising and reducing species present in the electrolytic cell and their standard electrode potentials.

The different products of electrolysis result from the oxidizing and reducing agents available in the electrolytic cell, influenced by the respective standard electrode potentials. For reactive electrodes, the potential of the species involved in reaction determines which species will gain or lose electrons (i.e., be reduced or oxidized). For example, during the electrolysis of aqueous sodium chloride, H⁺ from water may be reduced to hydrogen gas over sodium ions due to its higher electrochemical potential.

Imagine cooking. Depending on the ingredients used (oxidizing or reducing agents), the final dish (products of electrolysis) will change entirely. Just as a chef picks which ingredient to add based on the desired taste, the electrochemical processes choose which ions to discharge based on their energetic favorability.

For example, if we use molten NaCl, the products of electrolysis are sodium metal and Cl2 gas. Here we have only one cation (Na+) which is reduced at the cathode (Na+ + e– ® Na) and one anion (Cl–) which is oxidised at the anode (Cl– ® ½Cl2 + e–). During the electrolysis of aqueous sodium chloride solution, the products are NaOH, Cl2 and H2.

When molten sodium chloride (NaCl) is electrolyzed, simple reactions occur: at the cathode, sodium ions are reduced to sodium metal, while chloride ions are oxidized at the anode to form chlorine gas. However, in aqueous solution, the presence of water changes things. The water provides hydrogen ions which can be reduced instead of sodium ions, leading to the production of hydrogen gas, sodium hydroxide, and chlorine gas. Thus, the electrolysis process can yield different products based on the physical state of the electrolyte.

Think of soda and water. When you drink soda (molten NaCl), you get a fizzy, sweet beverage (sodium metal and chlorine gas) instantly. But if you drink water (aqueous NaCl), you are hydrated but no fizz - and that's the difference; you're not getting the chlorine gas because water's presence changes how responses are preferred. Water directs the output more towards hydrogen.

There is competition between the following reduction reactions at the cathode: Na+ (aq) + e– ® Na (s) (E(ocell ) = – 2.71 V) and H+ (aq) + e– ® ½ H2 (g) (E(ocell ) = 0.00 V).

At the cathode during electrolysis of aqueous solutions, you have competing reactions; here, Na⁺ ions can be reduced to sodium, but H⁺ ions from water are energetically more favorable due to their higher reduction potential. Therefore, hydrogen gas is produced as a preferred product over sodium. This competition influences which product is formed based on the stability and energy considerations of the ions involved.

It's similar to choosing a film to watch. If two films (like Na and H reactions) are available, and one is critically acclaimed (more favorable), people are naturally inclined to watch that one first. If the other doesn’t have the same appeal, it won’t be chosen, similar to how products are formed based on energetic preferences during electrolysis.

The net reaction at the cathode may be written as the sum of the reduction of H+ and the splitting of water: H2O (l ) + e– ® ½H2(g) + OH– (aq).

The overall processes may be represented by combining the preferred reducing reaction with the water's dissociation, leading to the generation of hydroxide ions at the cathode during electrolysis of aqueous sodium chloride. The interplay between these reactions results in the formation of hydrogen gas and the hydroxide ion, demonstrating how conditions affect what is produced at that electrode.

Think of making a smoothie. When combining fruits and water, the end product isn’t just fruit; it’s the blended result of everything instead. Similarly, the electrolysis reaction combines results from both the reduction of H⁺ ions and the water, leading to a necessary adjustment to find the complete picture of the reactions happening.

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