Dr Bob
Could you check this please?
Voltaic cell---cathode is positive, accepts electrons, reduced, anode is negative, gives up electrons and is oxidized
Electrolytic cell------cathode is negative, accepts electrons and is reduced. Anode is positive, givesup electrons and is oxidized
I can't understand why in one cell the neg electrode is reduced and oxidized in the other and the same with the anode unless the electrolytic one is wrong.
thank you
You are correct with which is the anode and which is the cathode.
The explanation of the difference in the two cells is easy.
The DEFINITION of the anode is
"The anode is where oxidation takes place." Which is the anode and which the cathode has nothing to do with what the sign is. It is ONLY on which is oxidized and which reduced.
If you think about it, though, remember that the electrolytic cell is just the reverse of the voltaic cell so why wouldn't they be reversed?
In order to understand why the cathode and anode have different roles in voltaic and electrolytic cells, it's important to understand the fundamental principles of redox reactions.
In a redox reaction, reduction and oxidation occur simultaneously. Reduction involves gaining electrons, while oxidation involves losing electrons. In a voltaic cell, also known as a galvanic cell, a spontaneous redox reaction produces an electric current. This occurs through a chemical reaction that generates an electrical potential difference, also known as voltage, between the cathode and anode.
In a voltaic cell, the electrode at the cathode is positive and it attracts the negatively charged electrons of the redox reaction. As a result, the electrons are transferred from the anode (which is negative) to the cathode and flow through an external circuit, creating an electric current. The cathode, being the site of reduction, gains electrons and is reduced.
On the other hand, in an electrolytic cell, an external power source, such as a battery, is used to drive a non-spontaneous redox reaction. This allows for the process of electrolysis. In this case, the roles of the cathode and anode are reversed. The cathode in an electrolytic cell is negative and attracts the positively charged ions in the electrolyte solution. The external power source provides the necessary energy to force the ions to move towards the cathode, where reduction occurs. Consequently, the cathode in an electrolytic cell is reduced.
Likewise, the anode in an electrolytic cell is positive and repels the positively charged ions in the electrolyte solution. The external power source causes the positive ions to move away from the anode. As a result, the anode is oxidized as it loses electrons.
To summarize, in a voltaic cell (a spontaneous redox reaction), the cathode is positive, attracts electrons, and is the site of reduction, while the anode is negative, loses electrons, and undergoes oxidation. In an electrolytic cell (a non-spontaneous redox reaction driven by an external power source), the roles of the cathode and anode are reversed: the cathode is negative, attracts positive ions, and undergoes reduction, while the anode is positive, loses electrons, and undergoes oxidation.
I hope this explanation clarifies why the roles of the cathode and anode appear to be opposite in voltaic and electrolytic cells.