Conductometric Titration

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FACULTY OF AGRICULTURAL AND SCIENCE

DEPARTMENT OF CHEMISTRY

PRACTICAL COVER SHEET

  Conductometric Titration

Theory

Titration is explained as a technique where a solution of known concentration is used to determine the concentration of an unknown solution. Typically, the titrant (the known solution) is added from a burrete to a known quantity of the analyte (the known solution) until the reaction is complete [1]. Knowing the volume of a titrant added allows the determination of the concentration of the unknown. Often, an indicator is used to usually signal the end of the reaction, the endpoint. The is usually confusion between endpoint and equivalent point in titration. Endpoint in simple form is just the point where we should stop titration because the has been a physical change. Equivalent point is where the base and acid have been mixed we cannot see the equivalent point.

Before we go on defining what is conductometric titration we shall define what is conductometry. Conductometry is a measurement of electrolytic conductivity to monitor a progress of a chemical reaction. Conductometric has notable application in analytical chemistry, where now conductometric titration is just a technique [2]. Conductometric titration is a type of titration in which the electrolytic conductivity of the reaction mixture is continuously monitored as one reactant is added. The equivalence point is the point at which the conductivity undergoes a sudden change. Marked increases or decrease in conductance are associated with the changing concentrations of the two most highly conducting ions—the hydrogen and hydroxyl ions. The method can be used for titrating coloured solutions or homogeneous suspension, which cannot be used with normal indicators.

Conductive measurements began as early as the 18th century, when Andreas Baumgartner noticed that salt and mineral waters from Bad Gastein in Austria conducted electricity [3][4]. As such, using conductometry to determine water purity, which is often used today to test the effectiveness of water purification systems, began in 1776.Friedrich Kohlrausch further developed conductometry in the 1860s when he applied alternating current to water, acids, and other solutions. It was also around this time when Willis Whitney, who was studying the interactions of sulfuric acid and chromium sulfate complexes, found the first conductometric endpoint [3]. These finding culminated into potentiometric titrations and the first instrument for volumetric analysis by Robert Behrend in 1883 while titrating chloride and bromide with HgNO3. This development allowed for testing the solubility of salts and hydrogen ion concentration, as well as acid/base and redox titrations. Conductometry was further improved with the development of the glass electrode, which began in 1909 [3][4].

The principle of conductometric titration is based on the fact that during the titration, one of the ions is replaced by the other and invariably these two ions differ in the ionic conductivity with the result that conductivity of the solution varies during the course of titration [4]. The equivalence point may be located graphically by plotting the change in conductance as a function of the volume of titrant added. In order to reduce the influence of errors in the conductometric titration to a minimum, the angle between the two branches of the titration curve should be as small as possible. If the angle is very obtuse, a small error in the conductance data can cause a large deviation. The following approximate rules will be found useful. The smaller the conductivity of the ion which replaces the reacting ion, the more accurate will be the result. The larger the conductivity of the anion of the reagent which reacts with the cation to be determined, or vice versa, the more acute is the angle of titration curve [5]. The titration of a slightly ionized salt does not give good results, since the conductivity increases continuously from the commencement. Hence, the salt present in the cell should be virtually completely dissociated; for a similar reason; the added reagent should also be as strong electrolyte. applications of conductometry are discussed here, conductometry in analytical chemistry is used to measure the progress of chemical reactions [6]. Conductometric titration is carried out in order to measure the electrical conductivity of the reaction mixture. This type of titration gives:

• This type of titration is used to check water pollution in lakes as well as rivers.
• It is also used to check the alkalinity of the fresh water
• Salinity of the sea water can also be checked by this method.
• It is also used to trace antibiotics.
• Used for tracing microorganism in food microbiology
• To check the solubility of sparingly soluble salts.
• Purity of distilled water and de ionised water can determined. [6]

Procedure

a 25 ml of pipette was used to transfer 0.1M of HCl into a clean 100 ml beaker. The beaker was firstly cleaned with distilled water to avoid any error of result. A stirring bar was added and to and it was placed to magnetic stirrer.

 The conductive cell was dip to the solution it was observed that if the electrode where fully cover by the solution, then 10 ml of water was added to the solution so to that the solution covers the electrode. The reading of conductance cell was recorded at zero volume of base. The burette was filled with sodium hydroxide but firstly it was cleaned using sodium hydroxide itself, the concentration of the string base was 0.1 M. 0.25 ml was added to the HCl solution while starring and the resistance on the cell where done. This procedural was done 20 times.