Post Lab Discussion

• Titrimetric analysis

  • Determination of the volume of a solution of known concentration required to complete a chemical reaction with a substance being analyzed.
• Titrimetric analysis is also known as volumetric analysis.
• Analyte - chemical substance being analyzed
• Analyte is also termed as active constituent.
• Titrant - solution added to react with the substance being analyzed.
• Indicator - organic compounds used to determine the hydrogen-ion concentration and indicate a change in pH
• End point

  • a sudden change in the property of the reaction mixture
  • practical
• Primary standard

  • highly purified compound used as a reference material in titrimetric analysis
  • a substance of known purity
• Secondary standard

  • may be used in the standardization of a solution
  • not necessarily pure but exact concentration is known
• Secondary standard - used to know concentration
• Standardization

  • determination of the concentration of a solution
  • determination of normality or molarity of solution
• Titration

  • Act of measuring the volume of the titrant used in the assay
• Equivalence point

  • Theoretical point at which equivalent amounts of each have reacted
• Equivalent

  • defined such that one equivalent of one material will react exactly with one equivalent of another
• Standard solution

  • also known as volumetric solution or titrant
  • solution of known concentration
• Molarity

  • defined as the number of moles of solute per liter of solution
• Normality

  • number of equivalents of solute per liter of solution
• Titer

  • Weight of a substance chemically equivalent to 1 mL of a standard solution
• Types of titration

  • Direct
  • Residual
  • Blank
• Direct titration - involves the direct and stepwise addition of a standard titrant to the analyte.
• Residual titration involves reacting a standard excess titrant with an analyte solution of an unknown concentration, then reacting the excess (left over) titrant with an analyte of known concentration to determine the concentration of excess titrant.
• Blank titration

  • without an analyte being present, only the solvent used in the analyte solution
• Residual or indirect titration

  • uses another reagent
  • analyte’s concentration is determined by performing the reaction between the analyte and a certain amount of excess reagent
• Two types of Volumetric apparatus

  • made to deliver a definite volume of liquid
  • made to contain a definite volume of liquid

  Unit of capacity is in milliliter (mL)
• Sources of error in the use of Volumetric Apparatus

  • Rinse water adhering to the apparatus
  • Grease film and dirty apparatus cause irregularities in the delivery of liquids and distort the meniscus
  • Drainage of the liquid adhering to vessel wall
  • Parallax should be avoided to secure proper readings of the level of meniscus.
  • Temperature variations lead to changes in volume of liquids and vessels
  • Air bubbles can displace liquid
  • Heat can cause calibrated volumetric apparatus to suffer a slight permanent change in volume
  • Salts causes change in temperature
• Requirements for Titrimetric analysis

  • Reaction must be complete (K must be equal or greater than 10^8)
  • Must have an end-point detecting device (indicator)
  • Must be rapid
  • Must have a sharp end-point
  • The reaction must proceed in a stoichiometric manner.
• Indicators

  • to determine end-points in neutralization processes
  • to determine hydrogen-ion concentration
  • to indicate that a desired change in pH has been achieved
• Malachite green pH range is 0.0 - 2.0
• Methyl orange pH range is 3.4 - 4.4
• Methyl red pH range is 4.2 - 6.2
• Bromothymol blue pH range is 6.0 - 7.6
• Phenolphthalein pH range is 8.0 - 10.0
• Malachite green acid is yellow, and base is green
• Methyl orange acid is pink and base is yellow.
• Methyl red acid is red and base is yellow
• Bromothymol blue acid is yellow and base is blue
• Phenolphthalein acid is colorless and base is faint pink
• • Methyl - titrant is acid
  • Phenolphthalein – titrant is base
• Methyl yellow

  • Acid - red
  • Base - yellow
• Bromophenol Blue

  • Acid - yellow
  • Base - blue