Measurement of Transport Number by EMF Method
This method is based on the measurements of emf of cells containing the same electrolyte with and without transference.
Consider a cell without transference
H2(g.1atm)/Hcl(a1) Agcl (S) /Ag/Agcl(S) Hcl(a2) /H2(g,atm)
The emf of this cell is given by
where, 'γ' is the total number of ions and γ+ and γ− are the number of positive or negative ions produced by the ionization of one molecule of electrolyte; z+ and z− are the valence of the ion with respect to which the extreme electrodes are reversible. If this ion is positive, the positive signs apply through out but if it is negative, the negative signs are applicable.
In the above cell, by removing the intermediate electrodes, the cell becomes with transference and is represented by
H2(g.1atm)/Hcl(a1)//Hcl(a2) /H2(g,atm)
The emf of the cell is given by
From equation:1 and equation:2 we get
E+ / E = t± Equation: 3
The transference number of either a cation or an anion can be determined using the above equation: 3.
