Hi, I was wondering if someone could clear this up for me. Anodes and cathodes. Which is which?
I'm getting mixed information from different textbooks, review books, and websites and I'm confused.
My review book states that The cathode is negative and the anode is positive, but other resources tell me otherwise. The review book also has a diagram showing cathode rays (-) flowing in the direction of the anode (+). But online it says the direction of flow is always from the anode to cathode. Is that just the case outside the device?
This is a confusing point and most text books get it right; however, they often fail to CLEARLY define which system they are discussing. Here is the correct skinny.
By definition, the anode is where oxidation occurs. That is the ONLY definition that counts. It is the ONLY one that is correct in all situations.
Having said all of that,
a) in batteries, the anode is the negative electrode.
b) in electrolysis cells (electroplating), the anode is the positive electrode.
In my classes, it is/was usual that students coming in to college chemistry thought that the anode was positive and the cathode was negative. In fact, I was taught that in grade school and high school. The fact is we were ALWAYS talking about electrolytic cells. In college the prof starts talking about the anode (and it was clearly marked negative) and I came unglued.
Ah, that makes a bit more sense. Thanks for clearing it up for me.
I can definitely clear up the confusion for you. Understanding the terms "anode" and "cathode" can be confusing because their designations can vary depending on the context and the type of device you're referring to. However, there are some general rules that can help you understand their meanings.
In the context of electrochemical cells, such as batteries or electrolytic cells, the anode is typically the electrode where oxidation occurs. Oxidation involves the loss of electrons, so the anode is considered the site of electron loss and is therefore associated with a positive charge. Conversely, the cathode is generally the electrode where reduction occurs. Reduction involves the gain of electrons, so the cathode is considered the site of electron gain and is associated with a negative charge.
However, when it comes to electronic devices like diodes or vacuum tubes, the anode is usually associated with the positive terminal, and the cathode is associated with the negative terminal. This convention is based on the direction of current flow, which is opposite to the direction of electron flow. Electrons, being negatively charged particles, actually flow from the negative terminal (cathode) toward the positive terminal (anode), but conventional current flow is defined as the movement of positive charges from positive to negative.
So, when you see a diagram showing cathode rays flowing in the direction of the anode, it's referring to the flow of electrons, not the conventional current flow. The flow of electrons from the cathode to the anode is indeed the case within the device itself, but when we talk about the current flow in a circuit, we refer to the conventional current flow from the positive terminal (anode) to the negative terminal (cathode).
In summary, the designation of anode and cathode can vary depending on the context and the type of device you're referring to. In electrochemical cells, the anode is associated with electron loss (positive charge), while the cathode is associated with electron gain (negative charge). In electronic devices, the anode is typically associated with the positive terminal, and the cathode is associated with the negative terminal, based on conventional current flow.