Analysis

• Titration


  Analytical methods in which the volume of solution of known concentration consumed during an analysis is taken as a measure of the amount of active constituent in a sample being analyzed
• Terms used in titration analysis

  • Analyte or active ingredient
  • Titrant - a solution of known concentration added by means of a buret
  • Titration - the act of adding and measuring the volume of titrant used
  • Indicator - a chemical which changes color at or very near the end point in titration where equivalent quantities of analyte and titrant have reacted
  • Stoichiometric point or equivalent point - the theoretical point at which equivalent amount of each have reacted
  • End point - point at which titration stops. It occurs by a sudden change in some property of the reaction mixture
  • Standardization - determination of the concentration of a standard solution
  • Standard solution - a solution of known concentration expressed in Normality or Molarity
  • Primary standard - weighed sample of a substance of known purity
• Classification of Volumetric Methods

  • Neutralization methods
  • Acidimetry
  • Alkalimetry
• Neutralization Reactions


  Chemical reactions wherein an acid reacts with a base
• Products of neutralization reactions

  Salt and water
• Neutralization reactions


  • Weak acid and strong base, or vice versa
• Indicators


  Complex organic molecules
• Functions of indicators


  • Determines end points in neutralization processes
  • Determine hydronium ion concentration or pH
  • Indicates that a desired change in pH has been effected
• Indicator color change


  Dependent on hydrogen ion concentration, may not indicate absolute neutrality or completion of reaction
• Mixed indicators


  Some indicators do not give a sharp end point or color change. In such cases mixed indicators are used to sharpen up the color change.
• Mixed indicators


  • xylene-cyanol - MO bromcresol green-chlorophenol red)cresol red-thymol blue)(thymol blue-phenolphthalein)
• Titration curves


  The manner in which the pH of a solution changes during titration is best shown by preparing a graph in which the pH value is plotted on the y-axis and the values of titration on the x-axis
• Titration curve -are used for the purpose of determining end point for titrimetric assays.
• Equivalence point in a titration curve

  That portion where the shape of the curve is at the steepest
• Titer


  Defined as the weight of a substance chemically equivalent to 1-mL of a standard solution.
• Standard solutions


  Solutions of known concentrations which are expressed in terms of molarity or normality
• Acid standard solutions


  • HCI, H₂SO4, HCIO.
• Basic standard solutions


  • NaOH, KOH, Ba(OH)2
• HCI is preferable because H2SO4 produces precipitates
• Solutions of NaOH absorb CO₂ from air thereby changing the concentration rapidly, therefore use CO₂ free water as solvent.
• Phenolphthalein, Methyl Orange, Methyl Red-When a strong acid is titrated with a strong base.
• Phenolphthalein -Weak acid and Strong base.
• Methyl red-Weak base and Strong acid.
• No indicator or Mixed Indicator -Weak base and Weak acid
• Acidimetry- this is direct or residual analysis of bases using an accurately measured volume of acid.    
• Alkalimetry-this is direct or residual analysis of acids using an accurately measured volume of base.
• Direct Titration- substances to be analyzed in is directly determined by titration to an endpoint with a standard solution. 
• Residual titration or Back titration - this is used whenever the endpoint of a direct titration deviates appreciably from the stoichiometric points for some reason.
• Direct titration method- %=ml×N×Meq wt×100/wt of sample
• Residual titration method- %=(mLa×Na)-(mLb×Nb)×meq wt/wt of sample ×100
• Elemental Analysis -several important elements that occur in organic and biological systems are conveniently determined by methods that involve an acid or base titration as the final step.
• Carbon, nitrogen ,chlorine bromine ,and fluorine - generally the elements susceptible to this type of analysis are non-metallic and includes.
• Nitrogen - occurs in a wide variety of substances of interest in research industry and agriculture. Examples include amino acids proteins synthetic drugs fertilizers explosive soils portable water supplies and dyes.
• Kjeldahl method- most common method for determining organic nitrogen which is based on neutralization titration.
• The Kjeldahl method was developed by - a danish chemist in 1883
• Precipitation method (Precipitimetry)


  Saturation method where a desired constituent is precipitated from solution by means of a standard solution as precipitating agent
• Precipitation methods


  • Formation of insoluble material or precipitates to cause the reactions to go to completion to be quantitative in nature.
• Ksp (Solubility product constant)


  A specific type of ionization constant that pertains to saturated solutions containing slightly insoluble substances (production of precipitates)
• Ksp


  The product of the concentrations of the ions in a saturated solution of a slightly soluble salt, at equilibrium
• Values for Ksp are found in the book of Gilreath, qualitative analysis