Chapter A2 A2.5 – Electrolytic Cells

Electrolytic vs. voltaic an electrolytic cell is a system where a non-spontaneous redox reaction occurs recall that a reaction that is non-spontaneous will only occur if energy is added in an electrolytic cell, energy is added in the form of electricity Voltaic Electrolytic spontaneous? yes no requires energy? produces voltage? use energy source electroplating change in energy exothermic endothermic

Electroplating the metals, like gold, that are the most stable and corrosion-resistant are also the most precious (and expensive) if you want to manufacture a metal object that is resistant to corrosion it would not be cost-effective to make the whole thing out of gold instead, a thin coating of gold could be applied to the surface of a more affordable metal

Electroplating the object to be coated will be submerged in a solution of metal ions (e.g. silver ions) an external energy source supplies energy to the electrons to force them to flow from the electrode into the solution this turns the plating metal ions into metal atoms, which will accumulate on the surface of the object to be plated.

Electrolytic cells Step #1: electrons from the plating metal (e.g. gold) are attracted to the + electrode of the power source this leaves the Au(s) atoms short on electrons, which causes Au+(aq) ions to be added into the solution

Electrolytic cells Step #2: Step #3: electrons flow through the power source Step #3: electrons accumulate on the surface of the object to be plated

Electrolytic cells Step #4: Au+(aq) ions from the solution are attracted to the electrons on the object to be plated when they gain these electrons, they turn into solid gold again and form a gold coating

Electroplating electroplating is a particularly good way to protect metals that are easily oxidized, like iron metals that work as good electroplaters are chromium, platinum, silver and gold

Gold jewelry solid gold gold plated if you have a piece of gold plated jewelry, care must be taken to avoid any deep scratches deep scratches will expose the oxidizable metal underneath solid gold karats - pure gold is 24K gold is a soft metal, so it is often combined with other metals like brass (copper and zinc) and nickel to make it more durable the number of karats in the gold refers to how many 1/24th of gold it contains by law, every piece of gold jewelry must be stamped with the karat mark

Other uses for electrolytic cells refining metals a sample of impure metal (anode), pure metal (cathode) ions of the pure metal will travel from the anode to the cathode to build up the atoms of pure metal electrolysis decomposition of a compound by means of an electric current e.g. electrolysis of water makes it decompose into O2 and H2

Other uses for electrolytic cells producing non-metals non-metals, especially the halogens, are difficult to obtain in pure form because they are so reactive non-metal atoms will accumulate around the anode of an electrolytic cell recharging voltaic cells when you use a battery recharger, you are using an electrolytic cell to reverse the process that occurs normally in the voltaic cell you are literally re-charging the voltaic cell with a new supply of electrons