In conductometric titrations, the electrical
conductivity of an electrical solution is continuously monitored as one
reactant is added. The accurate endpoint of can be determined by detecting a
sudden change in the conductivity of the solution. It is particularly useful in
titrating weak acids against weak bases. According to Ohm’s law;
I = E/R
Also,
R ∝ l
R ∝ 1/A
Therefore;
R = ρ l/A
ρ = RA/l
I = Current, E= electromotive force, R= Resistance, l
= Length, A= cross section area, ρ= Resistivity
The reciprocal of resistivity is conductivity. It can
be expressed as K.
K = 1/ ρ
= 1l /
RA
= G l/A
G is the conductance.
In the titration, the conducting material is the
solution. So the conductance depends on the type of ions in the solution and
their concentration. If the solution is located between two electrodes at
constant distance and cross section area, conductance will increase when the
concentration of the solution decreases.
Also when l and A are constant it
is clear that,
K ∝ G
These conditions
can be obtained by using a conductivity cell that consisting a pair of platinum
electrodes connected to the conductivity bridge which provides current to the
cell. The meter will give out the calculated conductivity of the solution.
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