- Electrolysis Definition: Electrolysis is a process that uses electric current to cause a chemical change, often used in refining metals.
- Electrolytic Refining: This involves purifying metals like copper using an electric current to separate impurities.
- Electroplating: Electroplating coats objects with a metal layer using a similar process to electrorefining.
- Electroforming: Electroforming reproduces objects by depositing metal onto a mold to create a detailed metal shell.
- Application of Electrolysis: Electrolysis is applied in various industries for refining metals, electroplating, and electroforming objects.
Applications of Electrolysis
Electrolytic Refining of Metals
Electrolysis is used to refine metals, to electroplate objects and to electroform copies. In electrolytic refining a crude-metal anode, a dissolved salt of that metal and a pure-metal cathode separate the metal from its impurities.
Electrolytic Refining of Copper
The usual example of electrolytic refining of metals is electrolytic refining of copper. Blister copper from the ore is 98 to 99 % pure. electrorefining can raise that to about 99.95% for electrical use.
In electrolysis, impure copper is the anode, copper sulfate acidified with sulfuric acid is the electrolyte, and graphite-coated pure copper plates are the cathode.
Copper sulfate splits into positive copper ions (Cu+ +) and negative sulfate ions (SO4 − −). The copper ions move to the cathode, take electrons and deposit as copper atoms on the graphite surface.
The sulfate ions (SO4 − −) move to the anode, take electrons and form radical SO4. Radical SO4 cannot stand alone, so it reacts with the copper anode to form CuSO4. The CuSO4 dissolves and splits into copper ions (Cu+ +) and sulfate ions (SO4 − −). Those copper ions travel to the cathode, take electrons and deposit as copper atoms. Copper therefore moves from the impure anode to the cathode.
Some metallic impurities also combine with SO4, form a sulfate and dissolve in the electrolyte. Silver and gold are not attacked by the sulfuric acid-copper sulfate solution, so they fall as anode sludge or mud. At intervals the copper deposit is stripped from the cathode and the anode is replaced by a new block of crude copper.
NB :- In electrolytic refining, or electro-refining, graphite coats the cathode so the deposited metal can be stripped off. Electrolytic refining is a common application of electrolysis.
Electroplating
electroplating uses the same ion transfer as electrorefining. The cathode is the object that needs the metal coat instead of a graphite-coated starter plate. A brass article can be given a copper coat by electroplating it with copper electroplating.
Copper Electroplating
Copper sulfate in solution splits into positive copper ions (Cu+ +) and negative sulfate ions (SO4 − −). For copper electroplating the electrolyte is copper sulfate, the anode is pure copper and the cathode is the object, here a brass article. The copper rod goes to the positive battery terminal and the article to the negative terminal. Immersed in the solution, the rod is the anode and the article is the cathode. The article attracts Cu+ + cations. Those Cu+ + ions take electrons at the article surface and deposit as a copper layer. SO4 − − ions move to the anode and take copper into solution, as in electro-refining. Slow rotation of the article helps the coat stay even.
Electroforming
Electroforming reproduces an object by depositing metal on a mould. Take an impression in wax or a similar material. Coat the wax with graphite so it conducts. Use that mould as the cathode in the electrolyte. Metal then deposits on the graphite. When the layer is thick enough, remove the article and melt out the wax to leave a metal shell. Electroforming was used to copy gramophone record discs. The original cut was made in wax, then dusted with gold powder so it conducted. That mould went into a blue-vitriol electrolyte with a copper anode to make a master plate for stamping shellac discs.
