How Inert Electrodes Influence Electrolysis Products
The electrochemical cell that facilitates a chemical reaction via the induction of electrical energy is called an electrolytic cell. The process of carrying out non-spontaneous reactions under the influence of electrical energy is called electrolysis. Electrolysis is commercially essential as a stage for the separation of elements from the naturally occurring substances such as the ores with the help of an electrolytic cell. The voltage which is needed for the electrolysis to occur is known as the decomposition potential. In this article, we will learn about electrolysis, mechanism of electrolysis, and the process of electrolysis. Let us first learn about the electrolysis process in detail.
What is Electrolysis?
Electrolysis is a process by which the electric current is passed through a substance which effects sort of a chemical change. This chemical change is the one in which the substance loses or gains an electron, which means, it undergoes oxidation or reduction. This process is carried out in an electrolytic cell, which is an apparatus that consists of the positive and the negative electrodes held apart and are dipped into a solution containing the positively and the negatively charged ions.
The substance that is to be transformed might form the electrode, might constitute the solution or might be dissolved in the solution. Electric current, that is, the electrons enters through the negatively charged electrode or the cathode. The components of the solution travel to this electrode, combine with the electrons and are transformed or reduced. The products that are obtained can either be neutral elements or new molecules.
The components of the solution also travel to the other electrode, which is the anode, give up their electrons, and are transformed or oxidized to the neutral elements or new molecules. If the substance to be transformed is the electrode, then the reaction is often the one in which the electrode dissolves by giving up the electrons.
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Factors Affecting the Product of Electrolysis
Given below are the factors affecting the product of electrolysis.
The products of electrolysis depend on the material that is being electrolyzed. In simpler words, the nature of electrolyte decides the process of electrolysis. This process is fast for a strong electrolyte whereas for a weaker electrolyte an extra potential, otherwise known as overpotential, is required. Products of electrolysis depend on the value of this overpotential too.
The products of electrolysis depend upon the nature of electrodes as well. This means that, in the case of the inert electrode (for example, gold, and platinum), it does not participate in the reaction, whereas, in case the electrode that is used is reactive in nature, it takes part in the reaction.
Several oxidising and reducing agents present in the electrolytic cell affect the products of electrolysis.
The products of electrolysis depend on the standard electrode potentials of the different oxidizing and reducing agents that are present in the electrolytic cell.
In case there are multiple reactions, the product of electrolysis depends upon the standard electrode potential of several reactions that are taking place. For example, the electrolysis of an aqueous solution of sodium chloride. Out of the several multiple reduction reactions that are taking place, the reduction reaction that has the highest value of the standard electrode potential takes place at the cathode. Similarly, out of the several oxidation reactions, the oxidation reaction that has the lowest value of the standard electrode potential takes place at the anode.
Inert Electrode
Let us now learn about what is an inert electrode.
An inert electrode is an electrode which serves only as a source or sink for the electrons without taking part as a chemical role in the electrode reaction. Precious metals, mercury, and carbon are some of the elements that are generally used as inert electrodes. The inert nature of the electrode can often be questioned. However, the electrode may not take part in the reaction in the form of a reactant or a product but can still act as an electrocatalyst.
FAQs on Electrolysis Products: Complete Guide for Students
1. What are the products of electrolysis?
The products of electrolysis are the substances formed at the anode (oxidation) and the cathode (reduction) when an electric current is passed through an electrolyte. The specific products depend on three main factors: the nature of the electrolyte (e.g., molten salt vs. aqueous solution), the type of electrodes used (inert vs. active), and the concentration of the ions in the solution.
2. How can you determine the products formed at the anode and cathode during electrolysis?
To determine the products, you must consider the competing ions near each electrode. At the cathode (negative electrode), the cation with the higher standard reduction potential gets reduced. At the anode (positive electrode), the anion with the lower standard reduction potential gets oxidised. For aqueous solutions, you must also compare these potentials with the reduction of water (at the cathode) and oxidation of water (at the anode).
3. What are some examples of products formed during the electrolysis of different electrolytes?
The products vary significantly depending on the substance being electrolysed. Here are some common examples using inert (platinum) electrodes:
- Molten NaCl: Sodium metal (Na) at the cathode and Chlorine gas (Cl₂) at the anode.
- Aqueous NaCl: Hydrogen gas (H₂) at the cathode and Chlorine gas (Cl₂) at the anode. Sodium ions remain in solution.
- Aqueous CuSO₄: Copper metal (Cu) at the cathode and Oxygen gas (O₂) at the anode.
- Dilute H₂SO₄: Hydrogen gas (H₂) at the cathode and Oxygen gas (O₂) at the anode.
4. How does using an active electrode instead of an inert one affect the electrolysis products?
An inert electrode (like platinum or graphite) does not participate in the reaction; it only provides a surface for oxidation or reduction. An active electrode (like copper, silver, or nickel) can itself be oxidised. If an active anode is used, it may get oxidised instead of the anion from the electrolyte, thus changing the product at the anode. For example, in the electrolysis of aqueous CuSO₄ with a copper anode, the copper anode itself dissolves (oxidises) to form Cu²⁺ ions instead of oxygen gas being produced.
5. Why is sodium metal obtained from the electrolysis of molten NaCl, but not from an aqueous NaCl solution?
This happens due to a difference in preferential discharge. In an aqueous solution, water molecules are also present. At the cathode, both Na⁺ ions and H₂O molecules can be reduced. The standard reduction potential of water (-0.83 V at pH 7) is much higher (less negative) than that of Na⁺ (-2.71 V). Therefore, water is preferentially reduced to produce hydrogen gas (H₂) and OH⁻ ions, while sodium ions remain in the solution. In molten NaCl, there is no water to compete, so Na⁺ ions are the only species available for reduction, forming sodium metal.
6. What is the importance of overpotential in predicting electrolysis products?
Overpotential is the extra voltage required above the theoretical value to make a non-spontaneous reaction occur at a specific rate. It can sometimes change the expected product of electrolysis. For example, during the electrolysis of aqueous NaCl, the oxidation potential of Cl⁻ ions is theoretically lower than that of water. However, the oxidation of water has a high overpotential, meaning it requires significantly more voltage to proceed. As a result, Cl⁻ ions are preferentially oxidised to form chlorine gas, a product that would not be predicted by standard potentials alone.
7. What is the difference in products when electrolysing aqueous copper sulphate using platinum electrodes versus copper electrodes?
The product at the cathode remains the same in both cases, but the anode product changes completely.
- With Platinum (Inert) Electrodes: At the cathode, Cu²⁺ ions are reduced to form a solid copper deposit. At the anode, water is oxidised to produce oxygen gas (O₂).
- With Copper (Active) Electrodes: At the cathode, Cu²⁺ ions are still reduced to form solid copper. However, at the anode, the copper electrode itself is more easily oxidised than water. Therefore, the copper anode dissolves to form Cu²⁺ ions, replenishing the electrolyte. This process is the basis for electrorefining metals.
