electrolysis

Question 1

Electrolsysis

Answer 1

Electrolysis is the breakdown of an ionic compound in the molten or aqueous state by the use of electricity.

Question 2

criteria for electrolysis

Answer 2

• The conduction of electricity requires mobile, charged particles.
• In electrolysis these are ions.
• The ions must be mobile
• the ionic compound is molten
  or dissolved in water.

Question 3

electrolyte

Answer 3

ionic compound that is molten or dissolved in water that conducts electricity and undergoes electrolysis

Question 4

Electrolysis of Molten Compounds

Answer 4

Electrolysis is a REDOX reaction
REDOX means “reduction” and oxidation” which are two chemical reactions involving electrons. They occur together.
Reduction – gaining electrons
Oxidation – losing electrons

OILRIG - oxidation is loss, reduction is gain
LEO (the lion) goes GER – Lose electrons oxidation, gain electrons reduction

Question 5

rules at the cathode

Answer 5

If the metal in the ionic compound is more reactive than HYDROGEN, then hydrogen forms at the cathode.
If the metal is less reactive than hydrogen, then the metal forms

Question 6

rules at the anode

Answer 6

• If the solution is a concentrated halide solution (chloride, bromide, iodide) the halogen forms.
• If the solution is a dilute halide solution or doesn’t contain halide ions then oxygen gas forms.

Question 7

brine

Answer 7

• Brine is a concentrated sodium chloride solution (very salty water).
• It is obtained by partial evaporation of sea water or pumping water through salt mines.
• The products of the electrolysis of brine are what make it so useful

Question 8

electroplating

Answer 8

• Electroplating is the process involving electrolysis to coat one metal with another. Often the purpose of electroplating is to give a protective coating to the metal beneath it or as a decorative coat

Question 9

electroplating of silver

Answer 9

• To plate an object with a metal the cathode is made from the object that is to be electroplated
• The anode is made from the metal that is to be the coating
• The electrolyte must be a salt solution that matches the metal to be electroplated. In this example the electrolyte is silver nitrate as silver is being plated on to the statue.

Question 10

purification of copper reactions

Answer 10

anode- Cu(s) — Cu 2+(aq) 2e-

cathode- Cu 2+ + 2e- —— Cu(s)

Question 11

electrolysis in solutions reactions

Answer 11

hydroxide ions - 4OH-(aq) — 2H2O(l) + O2(g) +4e-

hydrogen ions - 2H+ +2e- — H2

Question 12

extraction of aluminium

Answer 12

• Aluminium is extracted from the ore bauxite. Bauxite is aluminium oxide mixed with impurities such as sand and iron oxide.
• The impurities are removed to give aluminium oxide (alumina)
• The aluminium oxide them undergoes electrolysis to produce aluminium.
  Aluminium cannot be reduced by carbon as aluminium is more reactive than carbon

Question 13

method of extracting aluminium

Answer 13

1- mining ore in queensland
2- purifying by dissolving in hydroxide
3- shipped to bluff
4- at the aluminium smelter, alumina is dissolved in cryolite and this gives the mixture a lower boiling point (900 C) and conducts better electricity
5- large amounts of electrical energy ardee passed through the mixture, the anodes are carbon rods, the cathode lining is graphite in a steel casing, passing of the electrical current causes electrolysis
6- molten aluminium is poured int ignots

Question 14

aluminium extraction reactions

Answer 14

cathode- Al 3+ + 3e- — Al
anode- 2O 2- — O2 + 4e-
overall- 4Al 3+ + 6O2- — 3O2 + 4Al