C2.7 Electrolysis Flashcards
What is electrolysis?
The breakdown of an ionic substance that’s molten or in solution by passing an electric current through it
What is an electrolyte?
The liquid which is required in electrolysis - they’re usually molten or dissolved ionic substances
What are the products of electrolysis?
Pure elements
Where are electrons lost/gained in electrolysis?
They are lost at the positive electrode and gained at the negative electrode
What reactions does electrolysis have?
Oxidation and reduction reactions
In a reduction reaction, are electrons lost or gained?
Gained
In an oxidation reaction, are electrons lost or gained?
Lost
What is the acronym for oxidation and reduction?
O.I.L.R.I.G - Oxidation is Lose, Reduction is Gain
In electrolysis, where would an oxidation reaction take place?
At the positive electrode
In electrolysis, where would a reduction reaction take place?
At the negative electrode
What do half equations show?
The reactions at the electrodes
What are the products made at the negative electrode?
The element of the positive ion in the electrolyte
What are the products made at the positive electrode?
The element of the negative ion in the electrolyte and the amount of electrons which were lost in order to turn this ion into an element
If hydrogen ions are present in an electrolyte along with a metal more reactive than hydrogen, what will form at the negative electrode? Why?
Hydrogen will be formed at the negative electrode, this is because more reactive elements are keener to stay as ions
If hydroxide ions are present in an electrolyte along with halide ions, what will form at the positive electrode?
Molecules of chlorine, bromine or iodine - if no halide is present, then oxygen will form at the positive electrode
What is produced from the electrolysis of sodium chloride dissolved in water? (3)
Hydrogen, chlorine and sodium hydroxide
Hydrogen, chlorine and sodium hydroxide are all products from the electrolysis of sodium chloride, what can they be used for? (3)
Chlorine is used for the production of bleach and plastics, and sodium hydroxide is a strong alkali which is in the chemical industry e.g. to make soap
In the electrolysis of sodium chloride, what happens at the negative electrode?
The positive hydrogen ions move to the negative electrode where they gain an electron and combine to become hydrogen molecules (H2*) - this is a reduction reaction
In the electrolysis of sodium chloride, what happens at the positive electrode?
The negative chloride ions are attracted to positive electrode where they lose an electron and combine to form chlorine molecules (Cl2*) - this is an oxidation reaction
In the electrolysis of sodium chloride, what ions remain in the solution?
The sodium ions stay in the solution because they’re more reactive than hydrogen, and hydroxide ions from water are also left behind - this combine to form sodium hydroxide
What is aluminium’s main ore?
Bauxite
After mining and purifying Bauxite, what is left behind?
A white powder, aluminium oxide - the aluminium has to be extracted from this using electrolysis
Why is aluminium oxide not just melted?
Because it has a very high melting point which would be expensive
Why is bauxite dissolved in molten cryolite before electrolysis?
Because it brings down the melting point drastically, which saves energy making the process cheaper and easier
What are the electrodes made of in the electrolysis of aluminium? Why?
They are made of graphite (carbon) because it is a good conductor of electricity
What is formed at the negative electrode in the electrolysis of aluminium oxide?
Aluminium
What is formed at the positive electrode in the electrolysis of aluminium oxide? What’s bad about this?
Oxygen is produced - this combines with carbon from the electrode to form carbon dioxide, this not only contributes to global warming, but also means that the + electrode gets eaten away and needs to be replaced
What is electroplating?
The process of using electrolysis to coat the surface of one metal with another metal
What is the negative electrode in electroplating?
The metal object you want to plate
What is the positive electrode in electroplating?
The pure metal you want the object to be plated with
What must be in the electrolyte for electroplating to work?
Ions of the of the plating metal
How does electroplating work?
The ions in the solution plate the metal, but the positive electrode replaces these ions back into the solution
Why would you want to electroplate something? (2)
Decoration e.g. silver is attractive but expensive, so ugly brass cups are coated in silver - they look the same but are cheaper, and conduction e.g. copper is used to plate metal for electronic circuits and computers
