Module 9: Titrimetry

• Titration


  The overall procedure for the determination of the stoichiometric or  equivalence point. Common laboratory method to determine the concentration of an  identified analyte.
• Titration


  Slow addition of one solution of a known concentration to another unknown concentration.
• Titrant


  The solution added or reagent generated in a titration (standard/known concentration).
• Titrand


  The solution to which the titrant is added (analyte/unknown concentration)
• End Point


  A point in the progress of the reaction which may be precisely located and  which can be related to the stoichiometric or equivalence point of the reaction; ideally, the  two should be coincident.
• End Point


  The point at which the indicator changes colour in the  coloumetric titration. 
• Equivalence point


  the point in a titration when the amount of added standard  reagent is equivalent to the amount of analyte. Equal to amount of standard and analyte.
• Indicator


  A reagent or device used to indicate when the end point has been reached (kasama ng titrant).
• Standard Solution


  a reagent of known concentration. Used in titrations and in many other chemical analyses.
• Back-titration


  a process in which the excess of a standard solution used to  consume an analyte is determined by titration with a second standard solution.
• Back-titration


  Often required when the rate of reaction between the analyte and  reagent is slow or when the standard solution lacks stability.
• Primary Standard


  is an ultrapure compound that serves as the reference material for a titration or for another type of quantitative analysis.
• Secondary standard


  is a compound whose purity has been determined by chemical analysis. The secondary standard serves as the working standard material for titrations and for many other analyses.
• Blank Titration


  titration procedure is carried out without analyte (e.g., distilled  water sample. It is used to correct titration error.
• Titration Methods


  are based on determining the quantity of a reagent of known  concentration that is required to react completely with the analyte. The reagent may be a  standard solution of a chemical or an electric current of known magnitude.
• Types of Titration

  • Volumetric Titrations
  • Gravimetric Titrations
  • Coulometric Titrations
• Volumetric Titrations


  involve measuring the volume of a solution of known  concentration (e.g., mol/L) that is needed to react completely with the analyte.
• Volumetric Titrations

  • Simple Titrations
  • Double Titrations
  • Back Titrations
• Simple Titrations

  • acid-base
  • redox
  • precipitation
  • complexometry
• Gravimetric Titrations


  the mass of the reagent (solution) of a known concentration  (e.g., mol/kg) is measured instead of its volume.
• Coulometric Titrations


  measuring total charge (current x time) to complete the redox reaction, then estimating analyte concentration by the moles of electron transferred. The “reagent” is a constant direct electrical current of known magnitude that consumes the analyte.
• Titrimetry

  • Principles: Fast solution reactions between analyte and a reagent; titration to  stoichiometric point by volumetric or coulometric methods; end-point detection by visual indicators, precipitation indicators or electrochemical means.
• Titrimetry

  • Apparatus: Burettes, pipettes, volumetric flasks, analytical quality chemical  balance, indicator electrodes and coulometric generating electrodes.
• Titrimetry

  • Applications: Very widespread for precise routine and non-routine analysis in  industrial and research laboratories. Typical uses: determination of acidic and basic impurities in finished products, control of reaction conditions in industrial  processes, mineral and metallurgical analysis. Relative precision 0.1–1%.
• Titrimetry

  • Disadvantages: Storage of large volumes of solutions, instability of some reagent solutions, need for scrupulously clean glassware.
• Steps in Titration: Acid-Base


  Detail of the burette graduations. Normally, the burette is filled with titrant solution to within 1 or 2 mL of the zero  position at the top. The initial volume of the burette is read to the nearest 0.01 mL.
• Steps in Titrations: Acid-Base

  Before the titration begins. The solution to be titrated, an acid in this example, is placed in the flask, and the  indicator is added as shown in the photo. The indicator in this case is phenolphthalein, which turns pink in basic  solution.
• Acid-Base Titrations

  To select an indicator for an acid-base titration it is necessary to know the pH of the end point before using equation (Ex. pH= 7.0 + 2.4 - 0.65 = 8.75).
• Visual Indicators of acid-base titratioons

  A) red

  B) yellow

  C) bromo-phenol blue

  D) 3.7

  E) yellow

  F) yellow

  G) methyl-red

  H) blue

  I) yellow

  J) colourless

  K) ca.11

  L) ca.12

  
• Redox Titrations (Oxidation-Reduction Titration)


  a laboratory method of determining the concentration of a given analyte by causing a redox reaction.
• Redox Titrations


  Used to analyze a wide range of  inorganic analytes. (Ex. Electrochemical cells or batteries)
• Applications of Redox Titrations

  It provides pharmacopeial methods for the assay unformulated drugs. It helps in Agriculture and in detergent manufacturing, etc. 

  Used for standardization or raw materials and intermediates used in drug synthesis.
• Applications of Acid-base Titrations 


  used in analytical methods where the analyte reacts to produce a stoichiometric amount of an acid or base which can then be titrated.
• Kjeldahl Method


  for nitrogen determination in organic compounds.
• EDTA Titration


  Areas of application are spread throughout the chemical field from water treatment and the analysis  of refined food and petroleum products to the assay of minerals and alloys.
• EDTA Titration


  USED TO DETERMINE THE CONCENTRATION OF METAL IONS IN A SAMPLE.
• Precipitation Titrations


  USED TO DETERMINE HALIDE IONS.
• Silver Nitrate (AgNO3)


  most widely used reagent giving  rise to silver salts which are characteristically sparingly soluble.
• Mohr Method


  formation of red silver chromate with the appearance of an excess silver ions.
• Volhard Method


  which uses the ferric thiocyanate color as an indication of the presence of excess thiocyanate ions