100 %
0 %

Published on March 12, 2014

Author: krakeshg

Source: authorstream.com

POTENTIOMETRIC TITRATION: POTENTIOMETRIC TITRATION By K.RAKESH GUPTHA CONTENTS: CONTENTS INTRODUCTION PRINCIPLE THEORY ELECTROCHEMICAL CELL TYPES OF ELECTRODES END POINT LOCATION IN POTENTIOMETRIC TITRATION RECENT ADVANCES IN POTENTIOMETRY WHAT IS POTENTIOMETRIC TITRATION: WHAT IS POTENTIOMETRIC TITRATION PT is an electrochemical method of analysis ,which deals with the measurement of electrical potential of an electrolyte solution ( analyte ) under the conditions of constant current. The measured electro potential is used for qualitative and quantitative analysis of the analyte. INTRODUCTION: INTRODUCTION Traditionally, analytical chemists have relied on the classical method of titrimetry to determine the composition of substances. These methods require no specialized equipment beyond a burette, beakers, heating, and filtration apparatus, and yet they can outperform many spectrophotometric methods in terms of precision. A titration can often yield a result which is both precise and accurate to 4 significant figures. PowerPoint Presentation: The type of titration we will focus on in this session is one that uses an electrode as an indicator. Electrodes can be made to be sensitive to one species only. For example, the pH electrode responds to changes in [H + ], and the fluoride electrode responds to changes in [F - ]. electrodes are available for nitrogen oxides, oxygen, phosphate, halides, glucose and a host of other species. These electrodes can be made to directly measure the concentration of a species in solution via the Nernst equation . These other electrodes function in basically the same way as a pH electrode. PRINCIPLE: PRINCIPLE “Potential of the given sample is directly proportional to the concentration of its electro active ions” TYPES OF POTENTIOMETRIC ANALYSIS: TYPES OF POTENTIOMETRIC ANALYSIS Quantitative analysis in potentiometry Determination of concentration of analyte by measuring the changes in EMF on addition of a titrant to the sample Measurement of concentration of H+ ions (pH determination). Qualitative analysis Analysis of given sample to detect the presence of certain ions using selective electrodes. THEORY: THEORY The electrode potential is generated by electrochemical cell and analyte. The value of this electrode potential is given by NERNST EQUATION. or PowerPoint Presentation: R is the universal gas constant (8.3145 J K -1 mol -1 ) T is the absolute temperature z is the number of moles of electrons involved in the reaction as written F is the Faraday constant (96 485 C per mole of electrons) The Nernst equation PowerPoint Presentation: At 298.15 K (25 °C), the numeric values of the constants can be combined to give a simpler form of the Nernst equation for an electrode under standard conditions ELECTROCHEMICAL CELL: ELECTROCHEMICAL CELL A device, which coverts the chemical energy into electrical energy. It used to generate potential and electric current from chemical reaction. CONSTRUCTION the electrochemical cell consists of two electrodes in contact with electrolyte solution. the current is generated by the chemical reaction which involves releasing and accepting of electrons at the two electrodes eg- Redox reaction. PowerPoint Presentation: for a complete electrochemical cell from which neglible current is drawn , the EMF is given by E cell =E reference +E indicator +E junction TYPES OF ELECTRODES: TYPES OF ELECTRODES REFERENCE ELECTRODES PRIMARY REFERENCE ELECTRODES STANDARD HYDROGEN ELECTRODE SECONDARY REFERENCE ELECTRODES SATURATED CALOMEL ELECTRODE (SCE) MERCUROUS SULPHATE ELECTRODE SILVER/SILVER CHLORIDE ELECTRODE MERCURIC OXIDE ELECTRODE. PowerPoint Presentation: INDICATOR ELECTRODE HYDROGEN ELECTRODE QUINHYDRONE ELECTRODE ANTIMONY OXIDE ELECTRODE GLASS ELECTRODE COMBINATION pH ELECTRODE OXIDATION REDUCTION ELECTRODE ION SLECTIVE ELECTRODE GLASS MEMBRANE ELECTRODE LIQUID MEMBRANE ELECTRODE SOLID STATE ELECTRODE DOUBLE MEMBRANE ELECTRODE REFERENCE ELECTRODES: REFERENCE ELECTRODES RE is defined as an electrode , which has a stable and fixed potential i.e the Potential of reference electrode , does not change on dipping into any solution. It is an oxidation / reduction half-cell of known and constant potential at a particular temperature. It gives the standard or known potential. Reference electrode is used as one half of the electrochemical cell for determining the potential of the given sample. The Standard Hydrogen Electrode (SHE): The Standard Hydrogen Electrode (SHE) As a direct result of this, the standard hydrogen electrode (SHE) is commonly used as a reference electrode. When coupled with an electrode, the potential difference measured is the electrode potential of that electrode, as the SHE establishes by definition the zero point on the electrochemical scale. The standard hydrogen electrode consists of a platinum electrode suspended in a sulphuric acid solution with a one molar concentration of H + . PowerPoint Presentation: Purified hydrogen is bubbled through to equilibrate the 2H + + 2e - = H 2  electrode reaction. The hydrogen electrode is linked via a salt bridge to the deaerated solution in which the nickel electrode is immersed. This permits charge transfer and potential measurement but not mass transfer of the acid solution in the electrode. Saturated calomel electrode (SCE): Saturated calomel electrode (SCE) The reaction is based on the reaction between this elemental mercury (Hg) and mercury(I) chloride (Hg 2 Cl 2 , "calomel"). The Nernst equation for this electrode can be expressed as PowerPoint Presentation: cell notation the electrode is written as Cl - (saturated)  | Hg 2 Cl 2(s)  | Hg (l)  | Pt The measured potential, E, of the SCE is +0.241 V (SHE) for a saturated chloride ion solution at 298 K INDICATOR ELECTRODE: INDICATOR ELECTRODE Indicator electrode indicates the potential or pH of a solution in comparison to a reference electrode of a known potential. GLASS ELECTRODE: GLASS ELECTRODE These consists of a thin glass bulb at the bottom that is selective to H + . Two reference electrodes (usually Ag/AgCl) measure the potential difference across the membrane. PowerPoint Presentation:  Glass electrodes must always be calibrated because the concentration of H + inside the glass is always changing. Must also account for junction potentials. Calibration is done using standard buffer solutions. PowerPoint Presentation: Scheme of typical pH glass electrode 1.a sensing part of electrode, a bulb made from a specific glass 2.sometimes the electrode contains a small amount of AgCl precipitate inside the glass electrode 3.internal solution, usually 0.1 mol/L HCl for pH electrodes or 0.1 mol/L MeCl for pMe electrodes 4.internal electrode, usually silver chloride electrode or calomel electrode 5.body of electrode, made from non-conductive glass or plastics. 6.reference electrode, usually the same type as 4 7.junction with studied solution, usually made from ceramics or capillary with asbestos or quartz fiber. Membrane/ion selective electrodes: Membrane/ ion selective electrodes The glass electrode can be modified suitably to a ion/membrane electrode. The composition of the membrane is changed by adding specific ions or synthetic substances or polymers thereby the electrode can be used for measuring cations or anions . Types of Ion-selective Electrodes: Types of Ion-selective Electrodes Glass membranes These are selective to H + and certain monovalent cations. Solid-state electrodes These are made of inorganic salt crystals. The inorganic salt is made such to have vacancies in its lattice structure. The vacancies allow the ion (needed to fill the vacancy) to migrate through the salt. PowerPoint Presentation: 3 . Liquid-based electrodes A mobile carrier transports the selected ion across a membrane impregnated with a liquid solution of the carrier. 4. Molecular (Compound) Electrodes These contain a conventional electrode surrounded by a membrane that isolates (or generates) the analyte to which the electrode responds. For example, a CO 2 electrode responds the change in pH due to the presence of the CO 2 . END POINT LOCATION IN POTENTIOMETRY: END POINT LOCATION IN POTENTIOMETRY GRAPHICAL METHOD ANALYTICAL OR DERIVATIVE METHOD EQUIVALENCE POINT METHOD GRAN’S METHOD PINKHOF-TEADWELL METHOD CONTINUOUS WAVELET TRANSFORM GRAPHICAL METHOD: GRAPHICAL METHOD FIRST DERIVATIVE METHOD: FIRST DERIVATIVE METHOD ∆E/∆V SECOND DERIVATIVE CURVE: SECOND DERIVATIVE CURVE GRAN’S METHOD: GRAN’S METHOD VOLUME OF TITRANT ANTILOG E APPLICATIONS: APPLICATIONS 1. Water analysis: Surface, Sea, ground, potable, and waste water. 2. Atomospheric analysis: Gases are absorbed in solutions aerosol is deposited on filters. 3. Sedimented dust and soil are tedious to prepare. 4. Analysis of foodstuffs. 5. Clinical analysis. PowerPoint Presentation: Determination of N-Compounds Determination of Sulfur and others Determination of Heavy Metals IP 2007 METHODS: IP 2007 METHODS Assay of aceclofenac Weigh accurately about 0.3 g and dissolve in 40 ml of methanol. Titrate with 0.1 M sodium hydroxide. Determine the end point potentiometrically (2.4.25). Carry out a blank titration. Assay of chloroquine: Assay of chloroquine Assay. Weigh accurately about 0.2 g and dissolve in 50 ml of anhydrous glacial acetic acid with the aid of heat (if necessary, heat under a reflux condenser). Titrate with 0.1 M perchloric acid, determining the end-point potentiometrically (2.4.25). Carry out a blank titration. 1 ml of 0.1 M perchloric acid is equivalent to 0.02579 g of C18H26ClN3,2H3PO4. Assay of Amiloride Hcl: Assay of Amiloride Hcl Assay. Weigh accurately about 0.25 g and dissolve in a mixture of 100 ml of anhydrous glacial acetic acid and 15 ml of dioxan and add 10 ml of mercuric acetate solution Titrate with 0.1 M perchloric acid, determining the end-point potentiometrically (2.4.25). Carry out a blank titration. 1 ml of 0.1 M perchloric acid is equivalent to 0.02661 g of C6H8ClN7O,HCl. Assay of cimitidine: Assay of cimitidine Assay. Weigh accurately about 0.25 g and dissolve in 75 ml of anhydrous glacial acetic acid. Titrate with 0.1 M perchloric acid, determining the end-point potentiometrically (2.4.25). Carry out a blank titration. 1 ml of 0.1 M perchloric acid is equivalent to 0.02523 g of C10H16N6S. REFERENCES: REFERENCES A.H.BECKETT&STENLAKE , PRACTICAL PHARMACEUTICAL CHEMISTRY,FOURTH EDITION-PART TWO. VOGELS,QUALITATIVE CHEMICAL ANALYSIS,INDIA EDITION. O.V.K.REDDY , PHARMACEUTICAL ANALYSIS, PULSE PUPBLICATIONS. www.elsevier.com www.bingimage.com www.google.com THANK YOU: THANK YOU

Add a comment

Related presentations

Related pages

Potentiometric titration - Wikipedia, the free encyclopedia

Potentiometric titration is a technique similar to direct titration of a redox reaction. It is a useful means of characterizing an acid. No indicator is ...
Read more

Potentiometrie – Wikipedia

Bei der potentiometrischen Titration (Maßanalyse mit potentiometrischer Indikation) taucht eine Indikatorelektrode (z. B. pH-Elektrode, Redoxelektrode) ...
Read more


CHEM 152 WINTER 2010 POTENTIOMETRIC TITRATIONS Exp #8 Potentiometric Titrations Rev W10 NF Winter 2010 Page 1 of 12 Fill-in, Prelab attached (p 12) Name
Read more

Experiment 17: Potentiometric Titration - Boston College

1 Experiment 17: Potentiometric Titration Objective: In this experiment, you will use a pH meter to follow the course of acid-base titrations.
Read more

Potentiometric titration @ Chemistry Dictionary & Glossary

Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function ...
Read more


2. POTENTIOMETRIC TITRATIONS . Electrodes used in potentiometric titrations The experimental setup for potentiometric measurement ...
Read more


Chemistry 135 Clark College Potentiometric Titrations Revised Spring 2005 NF Page 3 of 14 Weak Acid Titration Volume of NaOH pH 2.00 4.00 6.00
Read more

Thermometric titration - Wikipedia, the free encyclopedia

A thermometric titration is one of a number of instrumental titration ... the potentiometric titration of sulfate with barium chloride in various ...
Read more


EXPERIMENT #5: Potentiometric Titration Titration-1 MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Chemistry 5.310 Laboratory Chemistry EXPERIMENT #5
Read more

Potentiometrische Titrationen in Theorie und Praxis

Titration durch die zugesetzte Natronlauge genauso wie die Natronlauge selbst verdünnt, so dass sie sich stetig ändert. Es gilt somit nach der Zugabe ...
Read more