LC Chem 1.5 Electrolysis

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chemistry

Electrolysis

The use of electricity to bring about a chemical reaction

Electrolyte

Liquid in which electrolysis takes place. Usually an ionic solution but it can also be a fused [melted] ionic compound

Direct current

Provides the energy necessary to create or discharge the ions in the electrolyte

Electrodes

Electrical conductors which link between the electrical circuit and the electrolyte

Inert

Electrodes which do not react with the electrolyte e.g. Graphite and Platinum

Active

Electrodes which react with electrolyte e.g. Copper and Iron

Anode

Positive electrode. Positive because the battery sucks electrons out of it.

Cathode

Negative electrode. Negative because the battery pumps electrons into it.

Anion

Negative ion. Named because it is attracted to the opposite charge of the anode

Cation

Positive ion. Named because it is attracted to the opposite charge of the cathode

Reduction

Reaction at cathode

H2O + 2 e- --> H2 + 2OH-

Equation at cathode

Hydrogen (H2)

Gas released at cathode

Base (OH- ions)

Acid or base at cathode

Oxidation

Reaction at anode

2H2O --> O2 + 4H+ + 4e−

Equation at anode

Oxygen (O2)

Gas released at anode

Acid (H+ ions)

Acid or base at anode

Graphite

Electrodes used for electrolysis of Sodium Sulphate and Universal Indicator

Purple

Colour at Cathode with Sodium Sulphate and Universal Indicator

Orange

Colour at Anode with Sodium Sulphate and Universal Indicator

Pink

Colour at Cathode with Potassium Iodide and Phenolphthalein

Brown

Colour at Anode with Potassium Iodide and Phenolphthalein

2I- --> I2 + 2e-

Equation at anode due to the oxidation of KI to brown Iodine

Electroplating

The process of covering the cathode in metal

Anode

Electrode which loses mass as copper dissolves off

Cu --> Cu2+ + 2e-

Equation at anode during copper electroplating

Cathode

Electrode which gains mass as Cu is deposited on it

Cu2+ + 2e- --> Cu

Equation at cathode during copper electroplating

Electrode potential

The tendency of a metal to lose electrons, i.e. the tendency for a metal to be oxidised

Electrochemical series

A list of elements in order of their standard electrode potentials: Pretty Sally Could Marry A Zulu In Lovely Honolulu Causing Many Strange Gazes (except for calcium)

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