Section 2.2 Properties of Water

Polar Molecules  molecules that have a slight positive region and a slight negative region Hydrogen Bond  an attraction between a slightly positive hydrogen atom and a slightly negative atom (often oxygen or nitrogen) Life depends on hydrogen bonds in water

Properties Related to Hydrogen Bonds: −High Specific Heat - hydrogen bonds give water an abnormally high specific heat −This means that water resists changes in temperature −Water must absorb more heat energy in order to increase in temperature

−Cohesion - the attraction among molecules of a substance −Cohesion from hydrogen bonds makes water molecules stick to each other −You can see this when water forms beads on a recently washed car −Cohesion also produces surface tension (how a spider stays on water without sinking)

−Adhesion - the attraction among molecules of different substances −Water molecules like to stick to other things −Adhesion helps plants transport water from their roots to their leaves because water molecules stick to the sides of the vessels that carry water

Solution  a mixture of substances that is the same throughout (a homogenous mixture) Solvent  the substance in a solution that dissolves the other substance −The substance that is present in the greater amount in a solution Solute  the substance in a solution that is dissolved −The substance that is present in the lesser amount in a solution Many compounds dissolve in water

Some compounds for acids and bases Acid  a compound that releases a proton (H + ) when it is dissolved in water. It increases the concentration of H + in a solution. Lower on the pH scale (0 – 6.9) Neutral  a compound that releases an equal amount of H + and OH -. Located at 7 on the pH scale. Base  a compound that removes H + from a solution (has more OH - ). Higher on the pH scale (7.1 – 14)