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Uploaded byJasmine Chaudhary
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Fundamentals of Volumetric Analysis.pdf

Volumetric analysis is a quantitative method to determine the concentration of an unknown substance by measuring the volume of a standard solution required for a complete chemical reaction. It involves titrating a solution of known concentration against the analyte until the endpoint is reached, as indicated by an indicator. This allows the concentration of the analyte to be calculated. The document discusses the different types of volumetric titrations including acid-base, redox, precipitation and complexometric titrations. It also covers key concepts such as standard solutions, titration curves, and methods to determine the endpoint of the reaction.

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Volumetric Analysis Dr. Jasmine Chaudhary Associate Professor MMCP, MM(DU), Mullana
 Analysis in which completion of reaction is determined by measuring volume.  It is commonly used to determine the unknown concentration of a known reactant.  It is a method of quantitative analysis in which one reactant of known concentration (standard solution) is added from the burette to the solution in conical flask whose concentration is to be determined until a required reaction is completed. The point at which the reaction is completed is called end point (equivalence point). Knowing the volume of the titrant, concentration of the unknown substance can be determined.  Also known as titrimetric analysis.  It was first introduced by Jean Baptiste Andre Dumas, a French chemist to determine the proportion of nitrogen combined with other elements in organic compounds.
Advantages  Needs a simple apparatus.  Cost effective method  Precision is better than instrumental methods.  When sample is very small and only one analysis is to be performed, simple titrations are often preferable.  Unlike instrumental methods, the equipments doesn’t require constant recaliberation. Disadvantages  Less sensitive and less selective than instrumental methods.
 Depending upon the reaction, volumetric titrations are further divided into 4 classes  Acid Base Titration  Redox Titration  Precipitation Titration  Complexometric Titrations  When the reaction involves an acid and a base, the method is referred to as an acid-base titration.  When the reaction involves oxidation and reduction, the method is referred to as a redox titration.
• Acid-base Titrations: The strength of an acid can be determined using a standard solution of base is called as acidimetry. In the same way, the strength of a base can be found with the help of standard solution of an acid is known as alkalimetry. The acid base titration is based on the reaction that neutralization between a base or an acidic and analyte • Redox Titrations: The redox titration is also known as an oxidation- reduction reaction. In this type of titration, the chemical reaction takes place with a transfer of electrons in the reacting ions of aqueous solutions.
• Precipitation Titrations: The titration is based on the insoluble precipitate formation when the two reacting substance are brought into contact are called as precipitation titration. • Complexometric Titrations: This type of titration is similar to precipitation titration in that a solid precipitates out of the sample when a reagent is added. The difference is that in complexometric titration, the solid is formed more quickly and more completely than in precipitation titration, which reduces errors in measurement. Ethylenediaminetetraacetic acid, an acidic powder better known as EDTA, is commonly used in this type of titration because it readily bonds with metals.
Terms to know  Titrate: The substance to be analyzed is called titrate.  Titrant: The reagent of known concentration which is added to the solution of the substance to be analyzed is called titrant.  Titration Curve: A plot of solution pH versus titrant volume during a titration.  Titration: The process of finding out the volume of the titrant required to react completely with a known volume of solution (Titrate) under analysis is known as titration.  Indicator: Auxiliary agents used to determine the end point of titration. A species added to the analyte to give an observable change at (which is the endpoint) or near the end point.
 End Point (Equivalence Point): The point where the reaction gets complete. The end point is the point where the system changes when the moles of the reacting titrant exceed the moles of the substance being titrated.  Standard Solution: It is a solution of definite concentration or of known strength.  Standardization: It is a process whereby the concentration of a solution is determined by the known concentration of solution.  Titration Error: It is the smallest difference between equivalence point and end point. This difference is because an indicator always produces the visual change either a little before or after the equivalence point.
METHODS TO DETERMINE THE ENDPOINT • pH indicator: This is a substance which shows the chemical change by changing the color. • A potentiometer: This is used to measure the electrode potential of the solution. These are used for redox titration. They show the end point with changing potential of the working electrode. • pH meter: It is a ion-selective electrode. In pH meter the potential of electrode depends on the amount of H+ ion present in the solution. The pH of the solution can be measured in the whole titration. • Conductance: The conductivity of solutions is also changed in titration and it depends on the ions present in the solution, mobility of ions and ions concentration. • Color change: In the redox reactions, the color of solution changes without use of indicator. This is due to different oxidation states of the product.
Conditions for Volumetric Analysis • All apparatus should be calibrated i.e. calibrating measuring vessels like volumetric flasks, pipettes, burette is necessary. • Chemical reaction must be simple and should take place quantitatively according to a well defined chemical equation. • Some indicators to determine end point should be used. • There should a marked change in some properties of the solution to be analyzed at equivalence point like when the reaction is complete, there should be a marked change in either color of the solution or some electrical property. • The reaction should be instantaneous (rapid) and complete (99%) under the experimental conditions maintained. • There should be no side reaction and if there is formation of interfering substances, these should be removed.
Fundamental concepts in Volumetric Analysis  Primary and Secondary standards  Preparation of standard solution.  Standardization  Ways of expressing concentration  Classification of volumetric methods  Steps involved in quantitative analysis
PRIMARYAND SECONDARY STANDARD SOLUTIONS Standards are materials containing a precisely known concentration of a substance for use in quantitative analysis. There are two types of standard solutions used in volumetric analysis: Primary Standard and Secondary Standard Primary Standard In titrimetry, certain chemicals are used frequently in defined concentration as reference solutions. Such substances/chemicals are referred to as primary standards. A primary standard is a compound of high purity from which a standard solution is prepared by direct weighing of quantity followed by dilution to give defined volume.
• A primary standard is a chemical or reagent which has certain properties such as a) It is considered extremely pure (high grade quality). Although 0.01-0.02% impurity is tolerable if it is accurately known. b) They should be easy to dry, obtain and purify. c) Highly stable (Should not react easily). d) They should be unaltered during weighing i.e. they should not be hygroscopic, oxidized by air or affected by CO2. It should maintain unchanged composition during storage. e) Has very high molecular weight so that they can be weighed easily and weighing errors can be negligible. f) They should be readily soluble to form standard solution. g) They should be readily available and inexpensive. h) Should be preferably non toxic
Examples for primary standards: 1. Acid-base titrations: Sodium Carbonate (Anhydrous), Potassium Hydrogen Phthalate, Oxalic acid 2. Redox titrations: Potassium Dichromate, Potassium Bromate, Potassium Iodate, Oxalic acid, Arsenic Trioxide 3. Precipitation titrations: Silver Nitrate 4. Complexometric titrations: Pure Metallic Zinc and Zinc Chloride Secondary Standard A secondary standard is a chemical or reagent which is generally less pure than the primary standard.
 A secondary standard solution is a solution in which concentration of dissolved solute has not been determined by weight of compound dissolved but by titration using primary standard solution. Examples include Sodium hydroxide: It is extremely hygroscopic and absorb moisture from atmosphere so, it cannot be used as a primary standard. Potassium permanganate (KMnO4): It is a good oxidizing agent, reactive and less stable. Due to its reactivity, its own oxidized product manganese oxide (MnO2) contaminates the content. That’s why it is unsuitable for being a primary standard. Sodium thiosulphate: Absorbs CO2 from the atmosphere and gets decomposed. A deposit of sulphur settles at the bottom.
Preparation of Standard Solutions Standard solutions are prepared by weighing out the desired amount of solute and then dissolving it in appropriate solvents usually water and then make up the volume with the same solvent. • It is more convenient to prepare dilute solution from concentrated solution using the relation M1V1(Concentrated solution)= M2V2 (Dilute solution) Preparation of 100ml of 0.1M NaOH from 1M NaOH 1x V1=0.1x100 V1= 0.1x100/1= 10ml So 10 ml of concentrated solution is when diluted with 90 ml of water, 0.1M solution of NaOH is prepared.
Standardization To determine the exact concentration of the prepared solution (secondary standard solution) using primary standard solutions. e.g. Standardization of 0.1N NaOH using 0.1N oxalic acid Standardization of 0.1N HCl using 0.1N sodium carbonate
Steps involved in quantitative volumetric analysis  Selection of method of analysis Require experience as well as scientific knowledge as the method selected should be accurate, simple, precise and economic.  Sampling and preparation of sample solution Sample is powdered and required amount of sample is weighed and dissolved in solvent under required conditions.  Elimination of interferences Interfering compounds should be eliminated from the solution for appropriate results.  Calibration and Measurement
 Calibration and Measurement All apparatus, equipment and instruments need to be calibrated before performing the analysis as the result will depend on the property measured which will be effective if proper calibration is done.  Observation and Calculation of Results Results observed are then computed using required formulas.  Evaluation of results
METHODS OF EXPRESSING CONCENTRATION OF SOLUTION The solubility of a solute is the amount of solute that will dissolve in a given amount of solvent at particular temperature to produce a saturated solution. Solute: A substance dissolved in another substance, usually the component of a solution present in the lesser amount. Solvent: A substance in which another substance is dissolved, forming a solution. The concentration of a solution is a macroscopic property, represents the amount of solute dissolved in a unit amount of solvent or of solution, and can be expressed in a variety of ways (qualitatively and quantitatively). Qualitative Expressions of Concentration Semi-Quantitative Expressions of Concentration Quantitative Expressions of Concentration
Qualitative Expressions of Concentration • A solution can be qualitatively described as Dilute: A solution that contains a small proportion of solute relative to solvent Concentrated: A solution that contains a large proportion of solute relative to solvent Semi-Quantitative Expressions of Concentration A solution can be semi-quantitatively described as: Unsaturated: A solution in which more solute can be dissolved Saturated: A solution in which no more solute can be dissolve