The cathode and anode (the positive and negative sides at either end of a traditional battery) are hooked up to an electrical circuit. The chemical reactions in the battery causes a build up of electrons at the anode. Electrons repel each other and try to go to a place with fewer electrons.

Anode, the terminal or electrode from which electrons leave a system. In a battery or other source of direct current the anode is the negative terminal, but in a passive load it is the positive terminal.

The direction of the electric current in a closed circuit is from the negative (–) terminal of the battery to the positive (+) terminal of the battery. Therefore, the battery terminals are where wires connecting the battery to the circuit should be attached.

Electrodes and ions The negatively charged electrode in electrolysis is called the cathode . The positively charged electrode in electrolysis is called the anode .

The molten aluminium sinks to the bottom of the cell, where it is tapped off. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, so they gradually burn away. As a result, the positive electrodes have to be replaced frequently. This adds to the cost of the process.

The Na+ ions and H+ ions are attracted to the negative cathode. Here the H+ ions pick up electrons, since hydrogen is less reactive than sodium. The hydrogen ions gain electrons (reduction)to form hydrogen atoms, which then pair up to form hydrogen molecules. The Cl- ions are attracted to the positive anode.

Hydrogen

(b) Zinc ions move towards the negative electrode where they gain electrons to produce zinc.

cathode. 1. The electrode carrying the negative charge in a solution undergoing electrolysis.

cathode

As charged objects, ions are attracted to opposite electric charges (positive to negative, and vice versa) and repelled by like charges. When they move, their trajectories can be deflected by a magnetic field.

Positively charged ions are called cations; negatively charged ions, anions.

When a crystal of an ionic compound dissolves in water, the ions separate. Again, the ions are free to move – so a solution of an ionic compound in water also conducts electricity.

Ions form when atoms gain or lose electrons. Since electrons are negatively charged, an atom that loses one or more electrons will become positively charged; an atom that gains one or more electrons becomes negatively charged. Ionic bonding is the attraction between positively- and negatively-charged ions.

The positive anode attracts anions toward it, while the negative cathode attracts cations toward it. Electrical current is carried by electrons in the wire and electrodes, but it is carried by anions and cations moving in opposite directions in the cell itself.

Calcium will form at the cathode and chlorine will form at the anode. This is because positive calcium ions are attracted to the negative electrode (cathode), where they gain electrons to form calcium atoms. At the same time, negative chloride ions are attracted to the positive electrode (anode).

Chlorine gas

Whether hydrogen or a metal is produced at the cathode depends on the position of the metal in the metal reactivity series :

1. the metal is produced at the cathode if it is less reactive than hydrogen.
2. hydrogen is produced at the cathode if the metal is more reactive than hydrogen.

Cryolite is another aluminium ore, but is rare and expensive, and most is now made chemically. The diagram shows a very simplified version of an electrolysis cell.

Cryolite: Can cause irritation of eyes, mucous membranes, skin and upper respiratory tract.