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Anode and cathode are the two categories in which electrodes are classified. The most significant difference between the anode and the cathode is that oxidation occurs at the anode and reduction occurs at the cathode . Many people tend to mistakenly consider that the anode is positive and the cathode is negative; however, the difference between anode and cathode is not simply based on the type of polarity. Here we explain why.
What is an electrode?
In order to understand what is an anode, a cathode and what is the difference between them, it is essential to first understand what an electrode is. The crucial element of an electrochemical cell that comes into contact with the electrolyte is called an electrode . The electrode acts as a metallic contact through which current enters and leaves the electrolyte. More specifically, it can be said that it is a surface in which a redox reaction occurs between the metal and the solution.
The electrode usually represents an electrical conductor/semiconductor within the electrochemical cell. Furthermore, it specifies the conducting phase where the transfer of charge carriers takes place. However, an electrode that loses electrons and is accepted by the electrolyte undergoes oxidation . On the other hand, when the opposite operation occurs, that is, when the electrode gains electrons that are released by the electrolyte, it undergoes a reduction .
What is an anode and a cathode
The terms cathode and anode were defined in 1834 by William Whewell, who adapted the words from the Greek kathodos , which means “down” or “down”, as the terminal through which the current leaves a device, since the anode is the terminal through which conventional current enters. Time later, these concepts were better defined.
An anode is a type of electrode that can be of positive or negative polarity depending on the type of cell. However, the anode is specifically defined as the electrode where oxidation , that is, the loss of electrons, occurs.
It is important to emphasize that we must take into account that the anode can never be defined, in general, as positive or negative, since its polarity depends on the type of cell.
Like the anode, the cathode can contain a positive or negative charge depending on the type of cell. In the case of the cathode , it is said to be an electrode where reduction occurs , that is, the gain of electrons. Like the anode, the cathode cannot be defined by its positive or negative polarity either, but the occurrence of reduction in an electrode implies that it is or is not a cathode.
Charge on the anode and cathode
As we have said, an oxidation reaction occurs at the anode. The oxidized species loses electrons, leaving this electrode with a buildup of electrons. Therefore, the anode is negatively charged. But unlike the cathode, there is a reduction response in which the diminished species gains electrons. Therefore, the electrode, that is, the cathode, lacks electrons and is therefore positively charged.
Main differences between the anode and the cathode
The key differentiating factor between the anode and the cathode is that the anode is the electrode where oxidation, i.e., the loss of electrons, occurs. While the cathode is the electrode where the reduction occurs, that is, the gain of electrons. On the other hand, the specific denomination of the anode as positive and the cathode as negative is wrong. In fact, the polarity of the terminals varies according to the type of cell used, that is, electrolytic or galvanic.
Now, in an electrolytic cell, the anode acts as a positive terminal while the cathode has a negative polarity. Thus, an anode attracts negatively charged particles while a cathode attracts positively charged particles. Finally, in the case of a galvanic cell, the anode has a negative polarity while the cathode acts as a positive terminal. Therefore, here the anode attracts the positively charged particles and the cathode attracts the negatively charged particles.
Fountain
Valera, I. (2019). What are the Anode and the Cathode .
