analysis exp 1 and 2

• Titrimetric Analysis


  Determination of the volume of a solution of known concentration required to complete a chemical reaction with a substance being analyzed
• Volumetric analysis


  Also known as Titrimetric Analysis
• Analyte


  Chemical substance being analyzed
• 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
• Primary standard


  Highly purified compound used as 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
• Standardization


  Determination of the concentration of a 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
• Volumetric Apparatus


  • Made to deliver a definite volume of liquid
  • Made to contain a definite volume of liquid
• Sources of Error in the Use of Volumetric Apparatus

  • Rinse water adhering to the apparatus
  • Grease films and dirty apparatus
  • Drainage of the liquid adhering to the vessel wall
  • Parallax should be avoided
  • Temperature variations
  • Air bubbles
  • Heat
  • Salts causing change in temperature
• Requirements for Titrimetric Analysis


  • Reaction must be complete
  • Must have an end-point detecting device (indicator)
  • Must be rapid
  • Must have a sharp end-point
• Indicators


  • To determine end-points in neutralization processes
  • To determine hydrogen-ion concentration
  • To indicate that a desired change in pH has been achieved
• Commonly Used pH Indicators

  • Malachite green
  • Methyl orange
  • Methyl red
  • Bromothymol blue
  • Phenolphthalein
• Rules in use of indicators
• Mixed Indicators


  • Methylene blue - Methyl red
  • Xylene cyanol - Methyl orange
  • Bromocresol green - Methyl red
  • Bromocresol green - chlorophenol red
  • Cresol red - thymol blue
  • Thymol blue - phenolphthalein
• Standard Solutions


  • Hydrochloric Acid
  • Sulfuric Acid
  • Sodium hydroxide
  • Potassium hydroxide
  • Barium hydroxide
• Standardization

  V x N = wt. of 1° std. / mEq wt. of 1° std.
• Preparation and Standardization of Acid and Alkali Solution

  1. Hydrochloric acid or sulfuric acid as standard acid solution

  2. Sodium hydroxide, potassium hydroxide, or barium hydroxide as standard alkali solutions

  3. Alkali solutions should be prepared carbonate-free and protected from carbon dioxide

  4. Acid solutions can be standardized titrimetrically or gravimetrically

  5. Alkali solutions can be standardized using acid solutions or potassium bipthalate
• Indicators are complex organic compounds used to determine end-points in neutralization processes, hydrogen-ion concentration, and indicate a desired change in pH
• Preparation and Standardization of 1N Sodium Hydroxide

  1. Primary standard: Potassium biphthalate

  2. Indicator: Phenolphthalein T.S.

  3. End point: Faint pink

  4. Use carbon dioxide free water to prepare solution

  5. Preserve solution in tightly stoppered bottle with soda-lime tube
• In the standardization of sodium hydroxide solution, the primary standard used was 0.67g potassium biphthalate and it used up 25.3mL of the solution. The concentration (N) of sodium hydroxide solution is 0.1297N or 0.1N
• Preparation and Standardization of 1N Hydrochloric Acid

  1. Primary standard: Sodium carbonate

  2. Indicator: Methyl red T.S.

  3. End point: Faint pink

  4. Boil solution to remove CO2 after first end point

  5. Titer value: 1mL 1N HCl is equivalent to 52.99mg of anhydrous sodium carbonate
• If 30 ml HCl were required in the titration of a 0.8560g sodium carbonate, the weight of the following pure reagents needed to neutralize 30ml of the hydrochloric acid solution would be: A. NaHCO3, B. KOH, C. CaO, D. Ba(OH)2