Chapter 4 - Electrochemistry
Electrolysis Definition
The decomposition of an ionic compound, when in molten or in aqueous solution, by the passage of an electric current.
Anode
Positive Electrode attracts ANIONS
Cathode
Negative Electrode which attracts CATIONS
Electrolyte
Molten or aqueous solution that undergoes electrolysis
Electrolysis of lead(II) bromide
Cathode: Lead ions form lead metal, Anode: Bromine ions make orange-red vapour
Electrolysis of concentrated aqueous sodium chloride
Cathode: Hydrogen ions turn to Hydrogen gas, Anode: Chloride ions turn into chlorine molecules
Electrolysis of dilute sulfuric acid
Cathode: Hydrogen gas forms at the cathode, Anode: Hydroxide ions form water and oxygen gas
What is formed at which electrode
Hydrogen gas and metals at cathode, non-metals at anode
Preference in electrolysis
Anode: Cl, Br, I are produced in preference to oxygen (hydroxide ions too). Cathode: Hydrogen is produced in preference over all metals except copper and iron(III) .
Metal Electroplating reasons
1) Improve their appearance
2) Resistance to corrosion
Electroplating process
Item to be plated is made the cathode and anode is metal going to be used for plating. When current is switched on, metal ions move from anode to cathode (object), hence plating it.
3 ways charge is transferred during electrolysis
1) Movement of electrons in the external circuit
2) Loss or gain of electrons at electrodes
3) Movement of ions in the electrolyte
ELectrolysis of aqueous copper(II) sulfate.
Cathode: Copper metal is deposited from copper ions. Anode: Hydroxide ions produce oxygen and water at anode. BLue solution loses its colour.
Function of a hydrogen-oxygen fuel cell
Uses hydrogen and oxygen to produce electricity with water as the only chemical product.
Advantages/Disadvantages of hydrogen fuel cell.
Advantages: Non-polluting water is produced, doesn't require external charging. Disadvantages: Difficult to store hydrogen gas, infrastructure does not yet exist, less durable, very expensive