Coarse copper (containing 99% copper) is pre made into thick plates as the anode, pure copper is made into thin plates as the cathode, and a mixture of sulfuric acid and copper sulfate is used as the electrolyte. After being electrified, copper dissolves from the anode into copper ions (Cu) and moves towards the cathode. Upon reaching the cathode, electrons are obtained and pure copper (also known as electrolytic copper) is precipitated at the cathode. Impurities in crude copper, such as iron and zinc, which are more active than copper, will dissolve with copper into ions (Zn and Fe). Due to the difficulty in precipitation of these ions compared to copper ions, adjusting the potential difference appropriately during electrolysis can avoid the precipitation of these ions on the cathode. Impurities such as gold and silver, which are less active than copper, are deposited at the bottom of the electrolytic cell. The copper plate produced in this way is called "electrolytic copper" and has extremely high quality, which can be used to make electrical products.