Electrolysis of molten salts
Electrolytes
A substance which, when molten or in solution, will conduct an electric current. are An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron). that are:
- in the A term used to describe a liquid substance (eg rock, glass or metal) formed by heating a solid. state (heated so they become liquids), or
- A substance is said to be dissolved when it breaks up and mixes completely with a solvent to produce a solution. in water
Under these conditions, the Electrically charged particle, formed when an atom or molecule gains or loses electrons. in electrolytes are free to move within the liquid or solution.
The decomposition (breakdown) of a compound using an electric current. is a process in which electrical energy, from a Also called dc. An electric current that flows in one direction only. (dc) supply, breaks down electrolytes. The free moving ions in electrolytes are attracted to the oppositely charged A conductor used to establish electrical contact with a circuit. The electrode attached to the negative terminal of a battery is called a negative electrode, or cathode. The electrode attached to the positive terminal of a battery is the positive electrode, or anode. which connect to the dc supply.
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Electrodes and ions
The negatively charged electrode in electrolysis is called the The negative electrode during electrolysis.. Positively charged ions move towards the cathode.
The positively charged electrode in electrolysis is called the The positive electrode during electrolysis.. Negatively charged ions move towards the anode.
Products of electrolysis
When ions reach an electrode, they gain or lose Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. As a result, they form The smallest part of an element that can exist. or A collection of two or more atoms held together by chemical bonds. of A substance made of one type of atom only.:
- positive ions gain electrons from the negatively charged cathode
- negative ions lose electrons at the positively charged anode
Molten lead bromide, PbBr2(l), is an electrolyte. During electrolysis:
- Pb2+ ions gain electrons at the cathode and become Pb atoms
- Br- ions lose electrons at the anode and become Br atoms, which pair up to form Br2 molecules
So lead forms at the negative electrode and bromine forms at the positive electrode.
Example
Predict the products of electrolysis of molten calcium chloride.
Positively charged calcium ions move to the negative electrode. Here, they gain electrons to form calcium atoms, so calcium is formed at the negative electrode.
Negatively charged chloride ions move to the positive electrode. Here, they lose electrons to form chlorine atoms. The atoms join up in pairs to form Cl2 molecules, so chlorine gas is formed at the positive electrode.
Question
Predict the products of electrolysis of molten aluminium oxide.
Aluminium will form at the negative electrode and oxygen will form at the positive electrode.