Electrolysis is the chemical effect of electricity on ionic compounds, causing them to break up into
simpler substances, usually elements.
An electrode is a conductor through which electric current is passed. It can be found in variable
forms, such as wires, plates, or rods. An electrode passes current between a metallic part and a
nonmetallic part of an electrical circuit.
A cation is a positive ion. An anion is a negative ion.
A cathode attracts the cations, and is therefore the negative electrode (because opposite charges
attract).
An anode attracts the anions, and is therefore the positive electrode.
An electrolyte is a chemical that conducts electrical current. They are typically in liquid form.
Commonly, electrolytes are solutions of acids, bases or salts.
Metal ions are positive, as they have lost one or more electrons. During an electrolysis experiment,
they form at the negative electrode, i.e. the cathode. Hydrogen ions also form at the cathode.
Non-metal ions are negative, as they have gained one or more electrons. During an electrolysis
experiment, they form at the positive electrode, i.e. the anode.
Click here to read more about ionic bonding.
Click here to read more about stoichiometry.
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ELECTROLYSIS OF MOLTEN LEAD(II) BROMIDE
Bromine is a non-metal; therefore, if it forms an ionic bond, it will gain an electron. It is in group 7,
and so it will gain just one electron to form a full outer shell. The “(ii)” after the word ‘lead’ signifies
that it has a charge of +2 (since it has lost two electrons). The charge on the lead ion is 2+ and the
charge on the bromide ion is 1-. Therefore, there must be two bromide ions in order to balance out
the charge. Therefore, we can deduce that the formula of lead(ii) bromide is PbBr2.
Lead is a metal, so therefore the lead(ii) ions will form at the cathode. The cathode is the negative
electrode, and gives away electrons. Each lead(ii) ion will form here and receive two electrons,
rendering the charge neutral and making it a lead atom.
Bromine is a non-metal, so therefore the bromide ions will form at the anode. The anode is the
positive electrode, and attracts electrons. Each bromide ion will form here and give away an electron,
also rendering its charge neutral and making it a bromine atom. Since bromine atoms by themselves
are so reactive, they will soon bond with another bromine atom to make Br2.
Therefore, the products of the electrolysis of molten lead(ii) bromide are bromine and lead:
Pb2+ + 2e2Br- - 2e-
Pb (reaction at the cathode)
Br2 (reaction at the anode)
OVERALL:
PbBr2(aq)
Pb(s) + Br2(g)
ELECTROLYSIS OF AQUEOUS COPPER(II) CHLORIDE
The same principle applies here.
Copper is a metal, so therefore the copper(ii) ions will form at the cathode. Here, each copper(ii) ion
will form and receive two electrons, rendering the charge neutral and making it a copper atom.
Chlorine is a non-metal, so therefore the chloride ions will form at the anode. Here, each chloride
ion will form and give away an electron, also rendering its charge neutral and making it a chlorine
atom. Since chlorine atoms by themselves are so unstable, they will soon bond with another chlorine
atom to form Cl2.
Therefore, the products of the electrolysis of aqueous copper(ii) chloride are copper and chlorine:
Cu2+ + 2e2Cl- - 2e-
Cu (reaction at the cathode)
Cl (reaction at the anode)
OVERALL:
CuCl2
Cu(s) + Cl2(g)