Biology Chapter 2, Section2 Dr. Steve W.Altstiel Water and Solutions Biology Chapter 2, Section2 Dr. Steve W.Altstiel

Objectives Analyze the properties of water. Describe how water dissolves substances. Distinguish between acids and bases.

Water in Living Things 70% of your body is made up of water. Water is the medium in which most cellular events take place. Water helps move nutrients and other substances into and out of your cells. Water has a high specific heat: takes a lot of energy to raise its temperature, and it retains this energy for a long time. Water is important for controlling temperature, thus enabling constant internal temperature. Water helps maintain homeostasis.

Cohesion and Adhesion Cohesion – the attraction of substances of the same kind. Hydrogen bonds b/n water molecules cause cohesion of liquid water – makes water form into droplets, and give it surface tension. Adhesion – an attraction between different substances. Powers the process of capillary action – water molecules moving upward in a narrow tube – stem of plant.

Aqueous Solutions Solution – a mixture in which one or more substances are evenly distributed in another substance. Water is a great solvent – it dissolves things well. Polarity – the polarity of water enables many things to dissolve in water. Ions, ionic compounds,, etc. Nonpolar molecules do not dissolve well in water – oil.

Acids and Bases Acids – compounds that form hydrogen ions (H+) when dissolved in water. Bases – compounds that reduce the concentration of hydrogen ions, or form hydroxide ions (OH-).

pH Scale Based on the concentration of hydrogen ions in solution. pH value between 0 and 14. pH of 7 = neutral – pure water Below pH of 7 = acidic Above pH of 7 = basic