MIDTERMS

• Titrimetric analysis


  Quantitative procedures based on measuring the amount of a reagent of known concentration that is required to react completely with the analyte
• Volumetric analysis


  Involves dissolving a weighed amount of sample and titrating the resulting solution with a standard solution
• Types of titrimetry


  • Volumetric titrimetry
  • Coulometric titrimetry
  • Gravimetric titrimetry
• Volumetric titrimetry


  Measuring the volume of a solution of known concentration that is needed to react essentially completely with the analyte
• Gravimetric titrimetry


  Measuring the mass of the reagent instead of its volume that is needed to react completely with the analyte
• Coulometric titrimetry


  Measuring the quantity of charge in coulombs required to complete a reaction with the analyte
• Titrimetric methods are widely used for routine determinations because they are rapid, convenient, accurate, and readily automated
• Titration


  The progressive addition of a standard solution to a solution with which it reacts
• Standard solution


  A solution with an accurately known concentration
• Standardization


  The process of determining the concentration of a standard solution
• Types of volumetric methods

  • Neutralization methods
  • Redox methods
  • Volumetric precipitation or precipitimetry
  • Compleximetric titrations or compleximetry
• Neutralization methods


  • Acidimetry - an acid is titrated with a standard solution of a base
  • Alkalimetry - a base is titrated with a standard solution of an acid
• Redox methods


  • Permanganate titrations
  • Dichromate and ceric titrations
  • Iodine titrations - direct and indirect
• Iodimetry (direct)


  Iodine solutions are used to titrate reducing agents being analyzed
• Iodometry (indirect)


  A solution containing iodide ions are added to a solution of an oxidizing agent and the iodine produced is titrated with standard thiosulfate
• Requirements for volumetric analysis

  • Accurate balance
  • Graduated cylinders and volumetric flask
  • Burettes
  • Standard solutions
  • Indicators
• Conditions for volumetric analysis

  • Reaction between standard and sample must be rapid
  • No side reaction should occur
  • Reaction must be complete
  • Abrupt change in some properties at or near the equivalence point
  • An indicator should be available
• Ways to carry out standardization


  • Direct standardization
  • Titration of a weighed portion of pure dry chemical
  • Titration of a measured volume of a previously standardized solution
• Primary standard


  A pure dry solid substance of known chemical composition used in the direct standardization of solution
• Requirements of a primary standard

  • Known purity and definite composition
  • Stable at the temperature employed for drying
  • Composition not affected by changes in humidity
  • Reacts quantitatively and in a known way with the solution to be standardized
  • Suitable indicator for the titration
• Properties of an ideal standard for titrimetric analysis

  • Concentration remains constant for a long time
  • Reaction with the analyte is rapid
  • Reaction with the analyte is nearly complete
  • Reaction with the analyte can be described by a balanced chemical equation
  • Method exists for detecting the equivalence point of the titration
• Standard solution or standard titrant


  A reagent of known concentration used in a titrimetric analysis
• Examples of standard solutions

  • HCl, HClO4, H2SO4, NaOH, BaOH, KOH
• Secondary standard


  A compound whose purity has been established by chemical analysis and that serves as the reference material for a titrimetric method of analysis
• Types of titration


  • Direct titration (dead stop)
  • Indirect titration
• Titration


  A process in which a standard reagent is added to a solution of an analyte until the reaction between the analyte and reagent is judged to be complete
• Distinct stages in titration

  • Preequivalence
  • Equivalence
  • Postequivalence
• Titration curves show how the pH of a solution changes as titrant is added
• 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
• Indicator


  A weak organic acid or a weak organic base whose undissociated form differs in color from its conjugate form
• Types of indicators


  • Internal indicators
  • External indicators
• Variables influencing indicator behavior

  • Temperature
  • Ionic strength of the medium
  • Presence of organic solvents
  • Colloidal particles
• Equivalence point


  The point in a titration when the amount of added titrant is chemically equivalent to the amount of analyte of the sample
• End point


  The point in a titration when a physical change occurs that is associated with the condition of chemical equivalence
• Titration error E1


  E1 = Vep - Veq, where Veq is the theoretical volume of reagent required to reach the equivalence point and Vep is the actual volume used to arrive at the end point
• Common concentrations of standard solutions

  • Molarity - no. of mol analyte present = no. mol standard reagent added
  • Normality - no. of eq. analyte present = no. eq. standard reagent added
• Buffer solution


  A mixture of weak acid and its conjugate base or a weak base and its conjugate acid that resists changes in pH of a solution