Electrolysis

Question 1

What is electrolysis?

Answer 1

The electrical decomposition of an electrolyte into its composite ions.

Question 2

Outline the industrial process of electrolysis.

Answer 2

1. The negative electrode (cathode) attracts positive ions, and donates electrons to them.
2. The positive electrode (anode) attracts negative ions, and accepts electrodes form them.
3. The electrodes are powered by a d.c supply, that the charges of the electrodes aren’t constantly changing.

Question 3

During electrolysis, which type of ions are reduced or oxidised?

Answer 3

Positive metal ions are reduced, and so are called the oxidising agents.

Negative non-metal ions are oxidised, and so are called the reducing agents.

Question 4

What does O.I.L.R.I.G. and what does it refer to?

Answer 4

Oxidation Is Loss. Reduction Is Gain

Refers to the movement of electrons.

Question 5

What conditons must be be met in order to use electrolysis?

Answer 5

1. Ionic compound must be aqueous or molten, because ionic solids cannot carry an electrical current as the ions are in fixed positions.
2. There must be a profitable amount of metal present in the ore for it to be electrolysed - electrolysis is very expensive as lots of energy is required to melt the ore and produce the required current.
3. Can and is generally only used for metals more reactive than carbon.

Question 6

Why is the electrolysis of aqueos solutions more complex?

Answer 6

The aqueous solutions have metal ions as well as positive hydrogen ions and negative hydroxide ions from the water.

Question 7

What two things could occur at the cathode if an aqueous solution is electrolysed?

Answer 7

1. If the metal is more reactive than hydrogen, then hydrogen gas is formed first.
2. If the metal is less reactive than hydrogen, then the metal is formed first.

Question 8

Outline the industrial process of the electrolysis of aluminium oxide.

Answer 8

1. Aluminium is dissolved in molten cryolite - this is easier to melt than aluminium, and so requires less energy and is, therefore, less expensive.
2. The electrodes used are made from graphite, a form of carbon.
3. Positive aluminium ions are attracted to the cathode, where they are donated electrons and form neutral atoms. They then sink to the bottom of the electrolysis tank.
4. Negative oxygen ions are attracted to the anode, where they donate electrons and form neutral atoms.

Question 9

Why do the electrodes used during aluminium extraction begin to show signs of wear?

Answer 9

The oxygen reacts with the graphite to form carbon dioxide (which contributes to global warming).
- The electrodes require constant maintenance because it begins to wear away.

Question 10

Why do electrolysis cells have lamps?

Answer 10

quality control - confirm electrical conductivity throughout circuit.

Question 11

Explain two other alternative methods of metal extraction other than carbon reduction and electrolysis.

Answer 11

1. Bioleaching (bacterial)
   
   • Bacteria feeds on ore and breaks down ionic bonds, separating the sulfates and the metals. As it cannot feed on pure metal, the metal is eventually left by itself.
2. Phytomining (plant-based)
   
   • Grow a plant over an area where there are thought to be some ores. After it grows for a period of time, the plan is the cut down and burnt, leaving a higher concentration of the metal in its ashes.

Question 12

Give the advantages and disadvantages of these alternative methods.

Answer 12

Advantages:
- Less harmful to the environment and use less energy
Disadvantages
- Take more time to produce a large quantity of metal