Cell Notation
1. Cell notation
It is also known as notation of voltaic cell. It is the short hand representation of a voltaic process/cell. It has following rules:
- Components of oxidation half-cell are written left to the components of reduction half-cell. Oxidation components consists of electrode which is anode, R (reactant) and P (product). Reduction components consists of electrode which is cathode, R and P.
- Both the half-cells. are separated by a double vertical line.
- Components of each cell are separated by a single vertical line or comma. Comma is used when both components are in same phase (aq-aq, s-s). Single vertical line is used when both components are in different phase (ag-l, aq-s).
- Physical state of each component is written as subscript to its symbol as Zn(aq).
- If concentration of any component is given, it is expressed in brackets after its symbol. E.g. Zn+2(aq) (0.1M) or H2(g) (1 atm).
- Electrodes are written as far right (cathode) and far left side (anode).
- A repeated component is written once only.
Components of oxidation half-cell | Components of reduction half-cell |
Anode | Cathode |
R and P | R and P |
1. Cell notation for a reaction between Zn and Cu:
In redox reaction, negative ions and salts do not take part thus, they are not represented in cell notation. Ions are always in aqueous form and electrodes in solid form.
2. Cell notation for a reaction between Ag and Cr
3. Cell notation for a reaction between Mn and I2
Problem of Cell Notation
In one compartment of a voltaic cell, a graphite rod was dipped into acetic acid solution of K₂ Cr₂O7 and Cr(NO3)3. In another compartment tin (Sn), was dipped in Sn(NO3)2 solution. KNO3 is salt bridge. Measurement indicates that Sn is negative.
Electrode (R) = Sn
Product (P) = Sn+2
Reaction at anode = Sn → Sn+2 + 2e-
Reduction compartment
Electrode (R) = Cr2O7-2
Voltaic Cell Diagram
Balance equation:
Cell notation: