Electrolysis

Oxford AQA GCSE Electrolysis

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Electrolysis by Mind Map: Electrolysis

1. Breakdown of a compound using an electric current.

2. Electrolyte

2.1. Ionic substance in which the ions are free to move and can be in form of:

2.1.1. Molten

2.1.2. Aqueous solution

3. Electrodes

3.1. Cathode (negative electrode)

3.1.1. This is where reduction occurs

3.1.1.1. Reduction is the gain of electrons

3.1.1.2. If H+ ions or metal ions are present, hydrogen gas will be produced if the metal is more reactive than Hydrogen.

3.2. Anode (positive electrode)

3.2.1. This is where oxidation occurs

3.2.1.1. Oxidation is the loss of electrons

3.2.1.2. If OH- and halide ions, molecules of Chlorine, Bromine and Iodine are produced, if not then Oxygen is given off.

4. Extraction of Aluminum

4.1. During Electrolysis

4.1.1. Aluminum is dissolved in molten cryolite

4.1.2. Oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, so they gradually burn away.

4.2. Half equations

4.2.1. At the Cathode, Aluminium ions receive electrons and are reduced to aluminium atoms: Al3+ + 3e– → Al

4.2.2. At the Anode, Oxide ions are oxidized to oxygen gas: 2O2– → O2 + 4e–

4.3. Aluminium is the most abundant metal on Earth, but it is expensive, largely because of the amount of electricity used in the extraction process.

5. Sodium Chloride in solution

5.1. During Electrolysis

5.1.1. Hydrogen ions H+ (from the water) are discharged at the negative electrode as hydrogen gas.

5.1.2. Chloride ions Cl– (from the dissolved sodium chloride) are discharged at the positive electrode as chlorine gas.

5.1.3. Sodium ions Na+ (from the dissolved sodium chloride) and hydroxide ions OH– (from the water) stay behind - they form sodium hydroxide solution.

5.2. Half Equations

5.2.1. At the cathode, the H+ cations are reduced when they gain electrons: 2H+(aq) + 2e- → H2(g)

5.2.2. At the anode, the Cl- anions are oxidized when they lose electrons: 2Cl-(aq) → Cl2(g) + 2e-

6. Half equations

6.1. A half equation is used to represent the reaction that happens at an electrode during electrolysis.

6.2. It shows what happens when ions gain electrons.

6.2.1. Positively charged ions gain electrons at the cathode. Some examples are:

6.2.1.1. Na+ + e- → Na

6.2.1.2. Pb2+ + 2e- → Pb

6.2.1.3. 2H+ + 2e- → H2

6.3. It shows what happens when ions lose electrons.

6.3.1. Negatively charged ions lose electrons at the anode. Some examples are:

6.3.1.1. 2Cl- → Cl2 + 2e-

6.3.1.2. 2O2- → O2 + 4e-

7. Extraction of Copper:

7.1. If a metal is less reactive than carbon, it can be extracted from its compounds by heating with carbon. Copper is an example of this.

7.1.1. Copper mostly occurs as sulfide ores, which are heated in air to convert them to copper(II) oxide.

7.1.2. Molten copper can be produced from copper oxide by heating with carbon

7.1.3. Copper oxide + carbon → copper + carbon dioxide. 2CuO(s) + C(s) → 2Cu(l) + CO2(g)

7.1.4. Copper oxide is reduced as carbon is oxidized.