1.3.1 Voltaic Cell – Simple Cell

1. A simple voltaic cell consists of two metal plates of different metals immerse in an electrolyte.
2. The metal which is higher in electrochemical series will become the negative terminal.
3. The atom of the metal which is higher in electrochemical series will release electron to form negative ions.
4. The electrons are then move to the other metal plate through the wire.
5. The metal which is lower in electrochemical series will become the positive terminal.
6. In positive terminal, the electrons will be released to the positive ions in the electrolyte.
7. In a voltaic cell, the negative terminal is the anode while the positive terminal is the cathode.

 Example

At Anode

Since magnesium is higher than copper in electrochemical series, hence magnesium is the negative electrode. In voltaic cell, the negative electrode is the anode.

Chemical Reaction

Magnesium atoms release 2 electrons to form magnesium ions.

Mg → Mg²⁺ + 2e

Observation

The magnesium strip (anode) erodes. Note: The electrons released are transferred to the cathode (copper) through the wire. As a result, current is produced and the galvanometer deflects.

At Cathode

Copper is lower than magnesium in electrochemical series, hence copper becomes the positive electrode. In voltaic cell, the positive electrode is the cathode.

Chemical Reaction

The positive ions that presence in the electrolyte is magnesium ions and the hydrogen ions. The hydrogen ions is lower than magnesium in electrochemical series, hence it will be selected to be discharged.

2H⁺ + 2e → H₂

Observation

Bubbles of colourless gas are evolved around the copper metal.