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Unit 1

Unit 1. Biochemistry Part II. Dissociation. Many substances dissociate (come apart) in water, in varying amounts. In solution, some molecules are intact, while others are ionized (gain or lose electrons). Water dissociates into ____ and ______ equally. Acids, Bases, Salts, and pH.

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Unit 1

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  1. Unit 1 Biochemistry Part II

  2. Dissociation • Many substances dissociate (come apart) in water, in varying amounts. • In solution, some molecules are intact, while others are ionized (gain or lose electrons). • Water dissociates into ____ and ______ equally.

  3. Acids, Bases, Salts, and pH • Acid: a substance that yields H+ when it dissociates in water • Base: a substance that yields OH- when it dissociates in water (or accepts H+) • Salt: a substance in which the H+ of an acid is replaced by another positively charged ion • pH: the acidity or alkalinity (basic-ness)

  4. Acids • Acids add H+ to a solution, increasing the H+ concentration • Example: an acid (hydrochloric) dissociates: HCl  H+ + Cl-

  5. Bases • Bases can release an OH- or accept an H+ • Bases reduce the amount of H+ in a solution • Examples: OH- + H+ H2O NH3 + H+ NH4+

  6. Salts • Replace the H+ in an acid: • Example: HCl + Na  NaCl + H+

  7. pH • Formula: • pH = -log [H+] • [H+] means concentration of hydrogen protons • If the pH = 6 then the concentration of H+/liter is 10-6 in a solution • pH Scale: 0-14 • Acidic = <7, Basic = >7, Neutral = 7

  8. Buffers • Buffers are substances that take up or release H+ or OH- to prevent swings in pH • H2CO3 is an important buffer • H2CO3 dissociates to H+ and HCO3- • The H+ is a base acceptor • The HCO3- is an acid acceptor • Why are buffers important to living organisms?

  9. Water • H2O is bonded covalently (polar covalent) • This gives water some unique and useful properties

  10. Water Properties • A Powerful Solvent: able to dissolve anything polar. • Polar compounds dissolve making them hydrophilic (water-loving) • Example: Phosphates • Non-polar compounds do not dissolve making them hydrophobic (water-fearing) • Example: Lipids (fats)

  11. Water Properties (con’t) • Adhesion: The attraction between water and other substances • Cohesion: The attraction between water molecules and other water molecules • These cause ____________ action • Water attracts to and climbs polar substances due to adhesion • Water drags up more water with cohesion

  12. Water Properties (con’t) • High Surface Tension: water is attracted to itself (cohesion) more than it is attracted to the air around it. • High Specific Heat: it takes a lot of heat to increase the temperature of water and a great deal of heat must be lost to decrease the temperature of water. • High Boiling Point: lots of energy are required to break the hydrogen bonds in order to change water from a liquid to a gas

  13. Water Properties (con’t) • Good Evaporative Coolant: because it takes a lot of energy for water to change from a liquid to a gas, the loss of water vapor takes a lot of energy (heat) with it. • High Freezing Point • Lower Density as a Solid Than as a Liquid: maximum density = 4 C, while freezing is 0 C. • This is why ice floats and lakes freeze over, but not from the bottom up.

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