From the anode to the cathode via the solution.
Explanation
Electroplating is the process of depositing a layer of a desired metal onto another material by means of electricity. This process utilizes an electrolytic cell where the electrical energy drives a non-spontaneous chemical reaction. In the specific case of copper electroplating, the setup involves a copper anode, a cathode (the object to be plated), and an electrolyte containing copper ions (typically copper sulphate).
Mechanism of Transfer:
- At the Anode (Positive Electrode): The anode is made of pure copper. When current flows, copper atoms from the anode lose electrons (oxidation) and dissolve into the solution as copper ions ($Cu \rightarrow Cu^{2+} + 2e^-$). This replenishes the copper ions in the electrolyte.
- Through the Solution: The positively charged copper ions ($Cu^{2+}$) present in the electrolyte are attracted to the negative electrode (cathode). They travel through the solution to reach the cathode.
- At the Cathode (Negative Electrode): The object to be plated serves as the cathode. Here, the copper ions gain electrons (reduction) and deposit on the surface as metallic copper ($Cu^{2+} + 2e^- \rightarrow Cu$).
Therefore, the physical transfer of copper mass occurs from the anode, into the solution as ions, and finally onto the cathode.
Key Takeaway:
In electroplating, the metal to be deposited is always the anode (sacrificial electrode), and the object to be coated is the cathode. The net material transfer is from the anode to the cathode via the electrolytic solution.