Biochemistry Continued

 Life could not exist without water.  Some functions of water include:  Control of body temperature  Keeps eyeballs moist  Lubricates joints  Absorbs shock  Protects brain and spinal cord from bruising

 Water can exist as a solid, liquid, or gas.  Its chemical structure is composed of 2 hydrogen atoms and 1 oxygen atom.  Because there is partial sharing of electrons between the 3 atoms, and because its molecular structure is asymmetrical, water is a polar covalent molecule.

 Due to its polarity, water is able to form bonds with other molecules.  These bonds between molecules are called intermolecular bonds.  These bonds are broken when solids melt into liquids, and liquids evaporate into gases.

 Water dissolves more substances than any other liquid.  Because of its polarity, water attracts other polar substances (including itself), and dissolves other polar substances.  Any substance that dissolves in water is called a solute.  Water, then, is a solvent.

 Often, the subscript “(aq)” is visible.  This subscript means that aqueous substances are soluble in water.  A polar molecule that can bond with water is called a hydrophilic molecule.  A nonpolar molecule that cannot bond with water is called a hydrophobic molecule.  Remember : “Like dissolves like”. (i.e., polar substances dissolve polar substances).

 mations/content/propertiesofwater/water.ht ml mations/content/propertiesofwater/water.ht ml  Worksheet…

 When 2 water molecules interact, one molecule gains a hydrogen (to become H 3 O +, hydronium ion) while the other loses a hydrogen (and becomes OH -, hydroxide ion).  This process is called the autoionization of water.

 Acids are defined as substances that increase the concentration of H + (or H 3 O + ) ions in solution.  Bases are defined as substances that increase the concentration of OH - ions in solution.

 When an acid is mixed with a base, the result is a neutralization reaction.  Neutralization reactions produce water and a salt.

 A solution with a pH of 7 is considered neutral (equal amounts of H 3 O + and OH - ).  Solutions whose pH is less than 7 are acidic (more H 3 O + ).  Solutions whose pH is greater than 7 are basic (more OH - ).