chem lab

• Buffers


  Weak acids/weak bases + their salts that resist changes if only small amounts of acids or bases are added
• Preparation of Buffers


  1. Most biochemical reactions in the body occur in an aqueous solution

  2. H+ concentration of an aqueous solution can affect the conformation and structure of substances & concentration of molecular and charged species which can affect the transport of substances in membranes and enzyme efficiency

  3. Mechanisms of the body to regulate H+ concentration: 1. buffer systems of the body, 2. action of the kidneys (excretion of acids and bases in the urine), 3. respiratory mechanisms (CO2 elimination regulates H+ concentration in the body fluids)
• Buffer solutions resist changes if ONLY SMALL AMOUNTS OF ACIDS OR BASES ARE ADDED
• pH


  The H+ concentration of an aqueous solution
• pKa


  The negative logarithm of the ionization constant of the weak acid
• pKw is 14 at 25°C
• Buffer systems of the body

  • HCO3 and H2CO3
  • HPO4 2- and H2PO4 -
• Blood plasma pH is 7.4, made up of acids and salts
• Spinal fluid pH is the same as blood plasma
• Importance of buffers


  • Regulating pH of the fluids and tissues of living organisms
  • Control of pH of culture media for microorganisms and tissues
  • Fermentation, electroplating, the manufacture of leather, photographic materials, and dyes
• pKa values


  • Acetic acid - 4.74
  • Carbonic acid - 6.1 to 10.4
  • Citric acid - 3.1 to 4.7
  • Phosphoric acid - 1.96, 6.67, 12.4
  • Sodium phosphate - 2.17, 7.21, 12.67