1. Chapter A2
A2.5 – Electrolytic Cells

2. 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

3. 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

4. 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.

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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