CONDUCTOMETRY.pdf

Electrochemistry  Electrochemistry - Introduction Electrochemistry deals with the study of chemical changes caused by the passage of an electrical current and/or the production of electrical energy by chemical reaction. Majorly it involves an oxidation–reduction reaction.  Electro...

Electrochemistry  Electrochemistry - Introduction Electrochemistry deals with the study of chemical changes caused by the passage of an electrical current and/or the production of electrical energy by chemical reaction. Majorly it involves an oxidation–reduction reaction.  Electrochemical Methods Electrochemical methods: are analytical techniques that use a measurement of potential, resistance, or current to determine an analyte’s concentration. It is a qualitative and quantitative methods of analysis Types of Electrochemical Methods Potentiometry methods: it measures the potential of a solution between two electrodes. The potential is then related to the concentration of one or more analytes. Types of Electrochemical Methods Voltammetry method: Voltammetry is the study of the current response of a chemical under an applied potential difference. Voltammetry encompasses a number of different methods, each of which can tell us about the kinetics and thermodynamics of Oxidation –Reducation Reaction. Types of Electrochemical Methods COULOMETRY METHODS: it is an electrochemical technique that measures the amount of electricity consumed or produced during an electrolysis reaction Types of Electrochemical Methods Conductometry methods: It measures the conductivity of electrolyte solutions in water or other solvents. It's based on the mobility of ions in an electric field, which is affected by their charge, size, mass, and extent of solvation. Conductometry Methods  Introduction It is an electrochemical method of analysis concerned with electrical conductance through an electrolyte solution. Electrical conductivity of an electrolyte solution depends on : Type of ions (cations, anions, singly or doubly charged Concentration of ions Temperature Mobility of ions  Principle Based on the conductance of electrical current through electrolyte solutions, in accordance with ohms law which states that the strength of current(I) passing through conductor is directly proportional to potential difference (E) & inversely to resistance (R). I – Ampere, E – Volts, R - Ohm  Principle Resistance (R): Is a measure of hindrance to the flow of electric charge R =1/C Specific resistance: (Resistivity) (ρ) Is resistance offered by a conductor of unit length and having unit cross section R ∞ l ⁄A R = ρ l/A Units – ohm - cm  Introduction Conductance (C): It is the ease with which the current flows through a conductor. Conductance is Reciprocal of resistance. Units - = = Moh’s  Conductivity Cell Conductivity Cell is used to hold the sample whose conductance is to be measured. These are constructed with metal electrodes placed at a fixed distance in either glass or plastic body and surrounded by an outer tube. The distance between the electrodes divided by their surface area is known as cell constant.  Conductivity Cell Cells are usually made of Pyrex or Quartz with Platinum Electrodes. Three Types: – Type A: consist of smaller electrodes separated by large distance for the measurement of high conductance accurately. – Type B: Simple dipping cell. – Type C: Large electrodes separated by smaller distance, useful for the measurement of low conductance (Low concentration).  Conductivity Cell Electrodes: – Platinum sheets, each of 1 cm2 are fixed at distance of 1 cm – The surface is coated with platinum black to avoid polarization effects and increase effective surface area.  Measurement of Conductance Conductance can be measured by measuring the resistance using a Wheatstone bridge.  Measurement of Conductance Solution whose Conductance is to be measured is taken in conductivity cell. Temperature need to be kept constant as conductance changes with temperature.  Measurement of Conductance We remove a (known) resistance (R) from the box and move the Jocky (K) on AB, such that there is NO or MIN. sound in the ear phone. Measurement of Conductance  Applications To measure the Basicity of Organic Acids. Solubility of Sparingly Soluble Salts To determine the ionic product of water Degree of dissociation of weak electrolytes Degree of hydrolysis Conductometric titrations.  Conductometric Titrations Conductometric titration is a laboratory method of quantitative analysis used to identify the concentration of a given analyte in a mixture. Conductometric titration involves the continuous addition of a reactant to a reaction mixture and the documentation of the corresponding change in the electrolytic conductivity of the reaction mixture.  Conductometric Titrations A sudden change in the conductivity implies that the stoichiometric point has been reached. The method of conductometric titration is very useful in the titration of homogeneous suspensions or coloured solutions as these titrations cannot be done with the use of normal chemical indicators.  Conductometric Titrations The strength of an acid can be determined via conductometric titration with a standard solution of a base. An example of a curve plotted for such a titration process is given below.  Conductometric Titrations Advantages and Disadvantages of Conductometric Titration This process is used in the titrations of very dilute solutions and weak acids. The end-point of this method of titration is very sharp and accurate This type of titration is applicable for solutions that are coloured or turbid, and for which the endpoint of the titration with normal indicators cannot be observed easily by the human eye.