SPM Chemistry

Voltaic Cell – Simple Cell

spmchemistry

Simple Voltaic 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.

Voltage of the Cell

Voltage of the cell

  1. The voltage of a voltaic cell depends on the difference between the electropositivity of the two metals.
  2. The greater the difference in the electrochemical series, the bigger the voltage produced.
  3. For example, the voltage of the cell consists of zinc and copper as the electrodes are higher than the voltage of the cell that uses iron and copper as its electrodes.

The Electrochemical Series

  1. The electrochemical series is an arrangement of metals based on the tendency of each metal atom to donate electrons.
  2. The higher the position of a metal in the Electrochemical Series, the greater the tendency of the metal atoms to donate electrons.
  3. The Electrochemical Series can be constructed based on
    1. The voltage between the two metals
    2. The ability of a metal to displace another metal from its salt solution