Properties of Water Chapter 2, Section 2

Water is a Polar Molecule  the uneven distribution of electrons between the oxygen and hydrogen atoms creates the polarity and gives water its bent shape

Hydrogen Bonds  the positive side of one water molecule is attracted to the negative side of another water molecule  water molecules can form up to four hydrogen bonds with adjacent water molecules

Capillary Action (think roots!)  Cohesion – attraction between molecules of same substance  Very strong in water due to hydrogen bonding!  Adhesion – attraction between unlike molecules  Because water is a polar molecule, it adheres very well to other polar molecules

Temperature Moderation Temperature is a measure of the random motion of particles in a substance.  Water heats up slowly because hydrogen bonds keep water molecules from moving around.  As water cools, it gives off heat slowly as hydrogen bonds reform.

Low Density of Ice  Unlike other liquids, water becomes less dense as it freezes.  Hydrogen bonds in ice keep water molecules spaced in a regular pattern

Water Can Dissolve Other Substances  Water dissolves other substances to form solutions  Solutions are uniform mixtures of two or more substances  Example: salt (NaCl) dissolved in water Water is the solvent Water is the solvent NaCl is the solute NaCl is the solute  Water can dissolve ionic compounds (salt)  Water can dissolve polar covalent compounds (sugar)  Water cannot dissolve non- polar substances (oils) Fig 2-9 on p. 42

Acids, Bases, and pH  A small percentage of water molecules break apart into ions in aqueous solutions H 2 O H + + OH -  If a solute increases the concentration of H+ ions in the solution, it is an ACID  If a solute decreases the concentration of H+ ions in the solution, it is a BASE  The pH Scale describes how acidic or basic a solution is:  Vinegar (pH of 3) is 10 times more acidic than tomato juice (pH of 4)