basic knowledge of conductometry titrations and its principle, instrumentation, & advantages and disdavantages of these titrations. Conductometry DR. . 3Principle The main principle involved in this method is that the movement of the ions creates the electrical. Conductometry-. Introduction. Ohm’s law. Conductometric measurements. Factor affecting conductivity. Application of conductometry. tometric titration.
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The conductance is defined as the current flow through the conductor. In other words, it is defined as the reciprocal of the resistance. This method is mainly used for the determination of the physico-chemical properties of the compounds. The main principle involved in this method is that the movement of the ions creates the electrical conductivity.
The movement of the ions is mainly depended on the concentration of the ions. This replacement of the ions with the other ions shows the conductance increase or decrease. This is done mainly by the replacement of the hydrogen ion with other cation. The theory is mainly based on Ohm’s law which states that the current I is directly proportional to the electromotive force E and inversely proportional to the resistance R of the conductor: The conductance is defined as the reciprocal of the resistance.
The resistance is expressed by the following equation: Then the molar conductivity is defined as the conductivity due to 1 mole and it is expressed by the following formula: The sample solution is placed on the cell which is composed of platinum electrodes. These are calibrated with the help of known conductivity of the solution, for example, standard potassium chloride solution.
conduchometry Cell constant is defined as the conductivity of the cell: The value is 0. The conductance of the sample solution is measured by the resistance measurement by the Wheatstone bridge.
The following are the different bridges used for the measurement of the conductance: It consists of a meter bridge wire AB with a fixed resistance R on both the ends. All these are operated by the battery. Headphone is used for the detection of the conductance difference. These conductivity princlple are made up of glass. These are commonly employed by dipping in the analyte solution.
It is composed of principls of electrodes placed at a constant distance. There are mainly three types of cells used as conductivity cells: This consists of the electrodes placed at a large distance and is used for the measurement of the high conductance. In this type, the cell is dipped in the sample solution to pdinciple the conductance in the titrations. In this type, large electrodes are placed with small distance. This type cell is mainly used for the measurement of the low conductance.
They conductometryy made up of glass fitted with the platinum electrodes. The princlple apparatus is composed of the following.
The electrodes are made up of platinum sheets. These electrodes are fixed in a constant distance and are sealed in the connected tubes. To avoid the polarisation effect, these electrodes are coated with the platinum black. On passing the current, chloroplatinic acid under goes electrolysis and the electrodes are blackened.
Then these electrodes are repeatedly washed with the distilled water and finally with the conductivity water. The conductivity water is condductometry water obtained by treating the distilled water with small amount of sodium hydroxide and potassium permanganate. Here the induction coil is used for princuple current. The sample solution is placed in the conductivity cell concuctometry constant temperature.
The temperature is maintained constant with the help of the thermostat. Then the cell is connected to the resistor box R and the alternating current is passed through the cell with the help of induction coil. Then the conductivity of the solution is measured by the following equation: The conductivity of the electrolyte increases with the temperature increase. This is because of the ions mobility by increasing the temperature. Concentration of the sample solution: The concentration of the solution is inversely proportional to the conductivity of the sample solution.
The conductance is decreased with the increase in the concentration. Hence diluted solutions are used for the conductivity measurements. Number ions present in the sample solution: This is mainly based on the dissociation of the compounds into ions. That is mainly of the number of ions present in the solution. The number of ions present connductometry the solution is directly proportional to the conductance.
Strong electrolytes completely dissociate into ions and have high conductance. Charge of the ions: Negative charge of the ions increases the conductivity where as the positively charged ions decreases the conductivity. Size of the ions: The conductivity is inversely proportional to the size of the ions.
That is the increase in the size of the ions increases the conductivity. Prinxiple this method, the conductance of the hydrogen ions and hydroxyl ions are compared with the conductivity of the sample solution. Strong acid with a strong base: The initial conductivity of the HCl solution is high because of the protons from the dissociation of the acid.
This shows the decrease in the conductivity. After completion of the reaction, the excess addition of the NaOH shows the increase in the conductivity.
The plot between the conductivity and the volume of the titrant shows the V-shaped curve. Strong acid with strong base curve. Strong acid with weak base: For example, titrations of the strong acid such as HCL with the weak base such as the ammonium hydroxide. The excess addition of the NH 4 OH does not show the change in the conductivity.
Then the plot between the conductivity and the volume of the titrant shows the plateau. Strong acid with weak base titration curve. Weak acid with a strong base: The weak acid such as acetic acid is titrated with the strong base such as sodium hydroxide. Then it shows the gradual increase in the conductivity by the addition of excess titrant. Then plot the graph between the conductivity and the volume of the titrant which shows the plateau.
Weak acid with strong base titration curve. Weak acid with weak base: The weak acid such as the acetic acid is titrated with the weak base such as ammonium hydroxide. The acetic acid is dissociated and it combines with the ammonium ion after dissociation of the ammonium hydroxide.
2. Conductometry – Pharmaceutical Analysis [Book]
This forms the ammonium acetate salt which shows the increase in the conductivity. After attaining the equivalence point, the addition of the titrant does not shows the conductivity change. The plot between the conductivity and the volume prindiple the titrant shows the plateau. Weak acid with weak base titration curve. When compared to the acid—base titrations, precipitate titrations are not that much accurate because of the more number of the interferences.
These are also known as the replacement titrations. The precipitate formation is taken conductlmetry the end point when the conductivity is measured.
Potassium chloride is titrated with the precipitating agent such as the silver nitrate solution. Initially the addition of the silver nitrate to the potassium chloride shows the stability in the conductivity and the excess of the silver nitrate addition increases the conductivity because of the formation of the single precipitate. In another case, the titration will form two precipitates.
For example, magnesium sulphate is titrated with the barium hydroxide and forms two precipitates: Initially the plot shows the decrease in the conductivity and then shows the increase in the conductivity. In this method, the decrease in the hydrogen ions concentration shows the decrease in the conductivity at the end point.
The titration of the ferrous ions with the dichromate ions. The hydrogen ions show sharp decrease in the conductivity. After the equivalence point, the addition of the excess of the titrant shows the stability in the conductivity. This was first proposed by Werner. In this method, the two end points are observed. First is the formation of the metal ion and the second one is the formation of the complex. The titration of the potassium chloride with the mercuric chlorate.
These are carried out as same as the acid—base titrations by using non-aqueous solvents. The titration of weak acids in the methanol by using tetra methyl ammonium hydroxide.