- Conductivity meter
- Conductivity cell
- Beaker
- Titrating flask
- Burette
- Pipette
- Glass rod
Reagent Required
- Standard N - Oxalic acid solution.
- HCl solution- unknown.
- NaOH solution- Intermediate solution.
Introduction
Conductivity measurements find application inwater treatment, leakage detection and interface detection.
Conductivity is a measure of the ability of a solution to carry electric current. The units are mho or
siemens. C = I / R, where C=conductance, R= resistance.
We know that Rα l/a or R=ρ.l/a where ρ is a constant and is known as specific resistance of the material of
the conductor.The inverse of specific resistance is known as specific conductance and is designated as
K(Kappa).
K = 1 / ρ
Specific conductance is the conductance of one cm cube of the material. But l/a is cell constant so
multiplying the measured conductance by cell constant, value of specific conductance is obtained.
When hydrochloric acid solution (HCl) is titrated with sodium hydroxide solution (NaOH), the highly mobile
hydrogen ions (λ°H+ = 350 ohm-1 cm-1) are progressively replaced by slower moving sodium ions (λ°Na+ = 50
ohm-1 cm-1) and the conductance of the solution decreases. After the end point, the conductance of the
solution rises sharply due to the presence of excess, highly mobile hydroxide ion (λ°OH- = 198 ohm-1 cm-1).
Thus the neutralization of a strong acid by addition of a strong base leads to a minimum conductance at the
end points. This is due to the disappearance of H+ ions and their replacement by slower moving Na+ ions of the
base followed by the presence of highly mobile OH-1 ions after the end point.
Reaction Involved
H+Cl-(aq) + Na+OH- (aq) → Na+Cl- (aq)+ H2>O