Under these conditions, the ions in electrolytes are free to move within the liquid or solution.
Electrolysis is a process in which electrical energy, from a direct current (DC) supply, breaks down electrolytes. The free moving ions in electrolytes are attracted to the oppositely charged electrodes which connect to the DC supply.
The negatively charged electrode in electrolysis is called the cathode. Positively charged ions move towards the cathode.
The positively charged electrode in electrolysis is called the anode. Negatively charged ions move towards the anode.
Molten lead bromide, PbBr2(l), is an electrolyte. During electrolysis:
So lead forms at the negative electrode and bromine forms at the positive electrode.
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.
Predict the products of electrolysis of molten aluminium oxide.
Aluminium will form at the negative electrode and oxygen will form at the positive electrode.
half equations are used to show whether an atom or ion has gained or lost electrons in a reaction.
During electrolysis, positive ions are attracted to the negative electrode (the cathode) and they gain electrons to form neutral atoms. For example, using lead ions:
Pb2+ + 2e- → Pb
Meanwhile, negative ions are attracted to the positive electrode (the anode) and they lose electrons to form neutral atoms or molecules. For example, chloride ions form chlorine molecules:
2Cl- → Cl2 + 2e-
Because chlorine gas is made from molecules which each have two atoms, the left of this equation shows two chloride ions which are needed to make the Cl2 molecule.