1.5 Analysing voltaic cell

The two ‘cells’ that you will learn during the course of SPM Chemistry are the voltaic cell/galvanic cell and the Danielle cell. The first is an electrochemical cell which produces electrical energy from chemical reactions occuring in the cell which consists of two different metal connected by a salt bridge (alternatively, half-cells separated by porous membrane). The Danielle cell is actually one example of galvanic cell, rather than commonly mistaken as another type of cell which is different from the galvanic cell. In this part, we’ll be learning all about cells.

[Tips: Be sure to note that Danielle cell is a subset of the voltaic cell. So if you were ever asked about the difference between a voltaic cell and Danielle cell, be sure not to describe them as two separate kind of cells. At best you could give examples of the general usage of voltaic cell against the more specialised usage of the Danielle cell, the general components involved and the specific components involved in a Danielle cell. Key point, Danielle cell is a subset of the voltaic cell.

Another key point to note is that the voltaic cell is also known as the galvanic cell. Although rare, but some students do describe them as different cells, which is wrong. Be sure to know that they are the same]

Example of Voltaic Cell/ Galvanic Cell

Voltaic Cell / Galvanic cell

It is an electrochemical cell which converts chemical energy –> electrical energy

Negative terminal: more electropositive (higher position in the electrochemical series)
Positive terminal: less electropositive (lower position in the electrochemical series)
Electrons released (more electropositive metal) through the wire to a less electropositive metal.

Example 1: Zinc plate and iron plate are placed in 1.0 mol dm³ of lead(II) nitrate, Pb(NO₃)₂ solution

Negative terminal (Anode): Zinc metal (Zinc plate dissolves to form Zn²⁺)
Positive terminal (Cathode): Iron metal (hydrogen ions will be selectively discharge to form hydrogen gas. It is because H⁺ is lower position than Pb²⁺ and Zn²⁺ in the electrochemical series)

Example 2: Magnesium plate and copper plate are placed in 1.0 mol dm³ of sodium chloride, NaCl solution

Negative terminal (Anode): Magnesium metal (Magnesium plate dissolves to form Mg²⁺)
Positive terminal (Cathode): Copper metal (hydrogen ions will be selectively discharge to form hydrogen gas. It is because H⁺ is lower position than Mg²⁺ and Na⁺ in the electrochemical series)

Daniell Cell

It is another example of a voltaic cell.

Solutions are connected by a salt bridge (inert electrolyte) or a porous pot.
The main function of a salt bridge / porous pot is to complete the circuit by allowing the movement of ions and prevent two aquoues solution is mixed.