conductometry

conductıvıty Conductivity (C) is the measure of the material’s ability to transmit electrical current. Conductivity is opposite to resistance (C= 1/R) and the unit of conductivity is S.m-1. It is commonly known that pure water does not transmit electric current because it theoretically does not contain ions. However, in practice, a conductivity around at microsiemens (µS) can be read because there are very few ions in pure water. Whether or not the water is pure can be understood by looking at the conductivity of it. The conductivity of ultra-pure water is 0.055 µS/cm. This value is around 56000 μS/cm in sea water when the conductivity of distilled water is around 0.5 μS/cm. Conductivity depends on the following parameters; Solvent viscosity The number of ions dissolved in the media Ion size Ion charge

conductometry Conductometry (Conductivity measurement) is an analysis method based on measuring of conductivity changes in the solution. The instruments used in conductivity measurement are called "Conductometer". Conductometers consist of an electrical source, the conductivity cell which is located in analysis solution and a resistance meter. The platinum electrodes coated with platinum black are used in the conductivity cell, which is the most sensitive region of the conductometry.

Conductometrıc tıtratıon Conductometric titration is a titration type in which the turning point is determined by utilizing the changes in conductivity of analyte in an unknown concentration during reaction with the titrant in a known contentration. Conductometric titration method is one of the most effective and suitable methods which are widely used in the analysis of dark colored or unclear solutions and in sedimentation reactions. Device Calibration The instrument must be calibrated before measurement. The electrical conductivities of the potassium chloride solutions prepared for this are measured. Then, the probe and thermometer of the device are immersed in the sample, swung to the right and left several times, and reading is done after fixing the value indicated by the device. Temperature compensating devices give the measured electrical conductivity values automatically at 25 oC. The conductivity values of potassium chloride at 25 ° C are as follows, depending on their concentration. The electrical conductivity of 0.001 M KCl = 146,9 µS/cm (meq= milliequivalent ) The electrical conductivity of 0.01 M KCl = 1413 µS/cm’dir. (meq= milliequivalent ) By measuring the electrical conductivities of KCl solutions prepared from these values, it can be checked whether the device is making healthy measurements.

Conductometrıc tıtratıon Strong Acid – Strong Base Titration HCl and NaOH solutions can be used in the titration of strong acid with a strong base. The following steps are followed for titration; Take 50 mL of the prepared analyte solution (HCl and NaOH) and place it in the conductivity cell of conductometry. The conductivity at the beginning is measured. The magnetic stirrer is operated. Titration is started by dropping a titrant solution (NaOH or HCl) in the burette. Conductivity is measured after each 0.1 - 0.2 ml of titrant is added. Conductivity values are plotted on the Y axis of the coordinate plane and titrant volumes (mL) are plotted on the X axis of the coordinate plane.

Weak acid – Strong base Titration As NaOH is added to the titration of a strong base with a strong acid, the hydrogen ion concentration decreases and the conductivity decreases rapidly to the equivalence point. After the point of equivalence, there will be more hydroxyl ions in the environment and the conductivity will increase again. The concentration of the acid is found by using the NaOH amount at the equivalent point obtained from the graph. The conductivity value obtained should be corrected according to the following formula, taking into consideration the dilution factor. If dilution does not exceed 10%, this may not be necessary. Weak acid – Strong base Titration A weak acid such as CH3COOH (analyte) can be titrated with a strong base such as NaOH (titrant). The following steps are followed for titration; Take 50 mL of the acetic acid solution and titrate with the adjusted NaOH solution. Conductivity values are noted after every 0.1-0.2 mL NaOH is added. Conductivity values are plotted against the titrant volume. The equivalence point is determined from the graph. Conductivityreal = Conductivitymeasured x V titrant + V anayte V analyte

CAlculatıons Two methods will be used for identification of the equivalence point. First, each conductivity value will be corrected to the real conductivity values according to the following formula. In the first method, the volumes of the additional titrant are plotted to the x axis on the millimetric paper and the conductivity values are plotted on the y axis. After that the equivalence point will be determined by drawing the cutting point with the aid of a ruler. In the second method, these values are loaded into a data processing program such as "Microsoft Excel" or "Open Office Calc". The data are divided into two parts, reduced in conductivity and increased in parts. The correct equations for these two separate data sets are derived The linear equations for these two separate data group are derived and the equations are equalized to find the breakpoint of these two lines. The x value found is the equivalence point. For example; When two linear equations are equalised eachother in the form of y =150x+47.6 and y = -150x+211.2 150x + 47.6 = -150x + 211.2 300x = 163.6 x = 0.545 Conductivityreal = Conductivitymeasured x V titrant + V anayte V analyte

references 1. Onur, Feyyaz; Analitik Kimya II, Ankara Üniversitesi Eczacılık Fakültesi Yayın No:101, s:135-149; Ankara 2011. 2. MEGEP (Mesleki Eğitim ve Öğretim Sisteminin Güçlendirilmesi Projesi) Kimya Teknolojisi; Elektrometrik Analizler, Ankara 2009.