Conductometry is the determination of the electrical conductance of an electrolyte solution by a conductometer instrument. It is generally used to identify the concentration of a given analyte (ionic species) in a mixture by measuring the electrolytic conductivity of the reacting species of the resultant products.
Conductometric titration means the addition of a reactant in a reaction mixture and measuring the corresponding change in the conductivity in the mixture. The electrical conductivity of an electrolytic solution is dependent on the free ions in the solution and the charge generated by these ions.
Types of Conductometric Titrations
The types of different Conductometric Titrations are mentioned below.
- Acid- base or neutralisation titrations
- Replacement or displacement titrations
- Redox titrations
- Precipitation titrations
- Complexometric titrations
- Non-aqueous titrations
1] Acid-Base or Neutralization Titrations
When the base is added to the acid solution, the conductance decrease due to the formation of the undissociated H2O molecule. After the equivalence point, the conductance increases due to the formation of OH- ions.
1. Weak Acid + Strong Base
Eg: CH3COOH vs NaOH
Initially, the conductance is low because of the poor ionization of acetic acid. With the addition of base, conductance decrease not only due to the replacement of H+ by Na+ but also suppresses the dissociation of acetic acid because of the common ion effect of acetate ion.
Then conductance increases on adding NaOH because it forms CH3COONa with CH3COOH. The conductance continues to increase to the equivalence point. The graph near the equivalence point is curved because of the hydrolysis of CH3COONa.
Beyond the equivalence point, conductance increases rapidly because of the addition of NaOH producing highly conducting OH − ions.
2. Strong Acid + Weak Base
Before the endpoint, conductance decrease, because the H+ is replaced by NH4+, and conductance, becomes constant due to common ion effects. NH4Cl decreases due to the ionization of NH4OH.
Eg: HCl vs NH4OH
3. Strong Acid + Strong Base
Eg: NaOH vs HCl
Before the addition of NaOH is added, the conductance increases due to the presence of highly mobile hydrogen ions.
When the base is added, the conductance decreases as the replacement of hydrogen ions. The conductance decreases till the equivalence point. At the equivalence point, the solution only has NaCl. After the equivalence point, the conductance increases as OH- ions are generated.
Conductance decreases due to the replacement of high conductivity hydrogen ions with poor conductivity sodium ions. Conductance increases due to the increase of hydroxyl ions.
4. Weak Acid + Weak Base
After the equivalence point, conductance virtually remains the same as the weak base becomes poorly ionized.
Eg: CH3COOH vs NH4OH
Conductance increases due to the excess of CH3COOH. Conductance remains constant due to the suppression of NH4OH by CH3COOH
2] Replacement or Displacement Titrations
If a weak acid is titrated by a strong acid, the anion of the weak acid is replaced by strong acid, and the weak acid is liberated in the undissociated form.
Ex- NH4CL vs NaOH
Similarly, if a strong base is added to the salt of a weak base, the cation of the weak base is replaced by the stronger one, and the weak base is generated in an undissociated form.
Ex- CH3COONa vs HCl
3] Redox Titration
Redox titration involves an oxidation-reduction reaction. The endpoint or the equivalent point in the redox titration is identified by an indicator or a potentiometer. Redox titration is used to identify the concentration of various unknown analytes as well as the potential of the reaction in redox titration. In this titration, the number of hydrogen ions decreases and the conductivity also decreased.
4] Precipitation Titration
In Precipitation titration titrant form a precipitate form during titration. If the titrant is in excess, it will automatically react with indicators such as potassium chromate, silver nitrate, or fluorescein ions, and form a precipitate. The principle on which the precipitation titration is that the amount of reagent added must be equal to the precipitate formed. Some of the most used precipitation reactions are Volhard’s method, Fagan’s method, and Mohr’s method.
5] Complexometric Titration
Complexometric titration is used to specify an endpoint of a titration by forming a colored complex by volumetric analysis. The process traces the mixture of metal ions in the solution.
The most common titrant is the EDTA (ethylenediaminetetraacetic acid) titrant. Complexometric titration is widely used for titrations because of the accurate identification of the equivalent points. This titration generally involves titrating phosphates, oxalates, and benzoates.
The commonly used indicators are Calmagite and Eriochrome Black T (EBT).
Mercury(II) nitrate was titrated with potassium cyanide solution. Before the equivalence point, one Hg(II) is replaced y 2 a K+ ion, and the conductance varies lightly. After the endpoint addition of K+ and CN-
Ions and conductivity increase sharply and the endpoint is determined by the intersection of these two lines.
6] Non-Aqueous Titrations
Non-aqueous titrations can be done by using conductometry.
Ex: a) Titration of weak bases vs. perchloric acid in dioxane-formic acid.
- b) Titration of weak organic acids in methanol vs. tetramethylammonium hydroxide in methanol benzene.
Advantages of Conductometric Titrations
- No need to determine specific conductivity and indicator
- Sharp color change is observed or dilutes solutions
- Endpointint is determined by graphical means with minimum error
- It can analysis of turbid suspensions
- Temperature must maintain constant throughout the titration.
Disadvantages of Conductometric Titrations
- Practically only a few specific redox titrations are done by this process as the conductivity of the solution by measuring high hydronium ion concentration.
- The accuracy of conductometric titration if the concentrations of the electrolyte are high.
Applications of Conductometric Titrations
- Checking water pollution in rivers and lakes
- Determining Alkalinity and Salinity of water
- Presence of Deuterium ion from water- deuterium mixture
- For tracing microorganisms and antibiotics
- Determine ash content in sugar juices