Electrolysis (updted)

• Electrolysis is the flow of electrical current in a conducting solution or molten liquid that causes chemical changes
• The conducting liquid is called an electrolyte and has free moving ions
• The conducting plates, bars, or wires inserted into an electrolyte are called electrodes
• Positive ions are called cations and are attracted to the cathode
• Negative ions are called anions and are attracted to the anode
• When current flows in an electrolyte, it is the ions that move and carry the electrical charge
• When current flows in the electrodes and wires, it is the electrons that move and carry the electrical charge
• Electrolysis can take place in ionic solutions as well as molten compounds
• The more concentrated the solution, the greater the ion flow rate
• Ion flow rate can be increased by increasing the potential difference or voltage across the cell
• Metals may be electroplated for aesthetics, protection, or both
• Electroplating is the process of coating one metal object with another using electrolysis
• Aesthetics involve making a metal shinier or giving it an attractive color, for example, jewelry is often plated with gold or silver
• Metal coating can be used for protection to resist corrosion, rusting, or general wear and tear, for example, car rims are electroplated for both shininess and protection
• Common metals used for electroplating include chromium (chrome), nickel, tin, zinc, and cadmium
• In electroplating, an electric current is passed through an electrolyte solution with two electrodes, the anode (positively charged) and the cathode (negatively charged)
• The metal for plating comes from the electrolyte solution, replenished by the metal anode
• Oxidation (loss of electrons) occurs at the anode, while reduction (gain of electrons) occurs at the cathode
• The speed of electroplating depends on the strength of the electric current, with a stronger current increasing the plating speed
• Not all metals will alloy with each other, so careful metal selection is important in electroplating
• Environmental concerns exist with some metals used in electroplating, such as chrome, which creates dangerous waste materials
• For electroplating to occur, the compound must be molten or dissolved in a solution to allow ions to move
• Half equations show what happens at one of the electrodes during electrolysis
• Oxidation occurs at the anode and reduction occurs at the cathode
• Redox reactions involve both reduction and oxidation occurring simultaneously
• Oxidation means the loss of electrons, while reduction means the gain of electrons
• For a redox reaction, electron transfer must occur with one substance losing electrons and another gaining electrons
• The silver nitrate solution contains Ag+ and NO3- ions
• Copper metal is oxidized as it loses two electrons to form Cu2+ ions
• Silver ions gain electrons to become reduced
• Half equations represent half of a redox reaction, either the reduction or oxidation reaction
• Spectator ions, like NO3- ions, have no effect on the overall reaction and are present on both sides of the equation
• In the redox reaction where iron III chloride oxidizes iodide ions to iodine solid:

  • Iron is reduced and gains an electron
  • Iodide ions are oxidized and lose electrons to form iodine