W ATER Water

W HY IS WATER IMPORTANT ????? All living things need water, and most organisms contain water. Most of our body weight is water! Biological processes take place only in water solutions! Water stores heat better than any other liquid!

W ATER ’ S STRUCTURE Water is made up of 2 hydrogen molecules and 1 oxygen molecule!

W ATER ’ S UNIQUE PROPERTIES Polarity The O atom has a stronger attraction for electrons than H does so the shared electrons stay closer to the oxygen atom Occurs with a molecule where the charges are unevenly distributed So the water molecule is polar because there is an uneven distribution of electrons between the hydrogen and oxygen

W ATER ’ S UNIQUE PROPERTIES Hydrogen Bonding Polar molecules attract each other The hydrogen atom is attracted to the oxygen atom on another water molecule One water molecule can have 4 hydrogen bonds

W ATER ’ S UNIQUE PROPERTIES Cohesion Attraction between molecules of the same substance Water is very cohesive because of the hydrogen bonding Water molecules on the surface are drawn inward so they can form beads on a smooth surface. Insects can walk on the surface water.

W ATER ’ S UNIQUE PROPERTIES Adhesion Attraction between molecules of different substances Due to hydrogen bonding Ex – water and glass Capillary action – adhesions that causes water to rise in a tube against gravity (water moves out of the roots to the stems and leaves)

W ATER ’ S UNIQUE PROPERTIES Solutions and Suspensions Mixture – material made up of two or more elements or compounds that are physically mixed together but not chemically combined There are 2 types of mixtures that can occur with water! 1. Solutions 2. Suspensions

S OLUTIONS AND SUSPENSIONS Solutions All components are evenly distributed throughout the solution! Solute – substance that dissolves (solid, liquid, gas) Solvent – substance in which the solute dissolves (liquid) Because of water’s polarity, it can dissolve both ionic compounds and polar compounds. WATER IS THE GREATEST SOLVENT ON EARTH!!

Cl - Water Cl - Na + Water Na + Section 2-2 Figure 2-9 NaCI Solution When a molecular substance dissolves in a liquid, the substance separates into its individual molecules!

Section 2-2 Figure 2-9 NaCI Solution Cl - Water Cl - Na + Water Na +

S OLUTIONS AND SUSPENSIONS Suspension Substances that don’t dissolve in water, but separate into pieces so small that they don’t settle out. Ex – sand in water, blood (mostly water but contains cells)

W ATER ’ S UNIQUE PROPERTIES Acids and Bases Water molecules can react and form ions. Water is neutral because the number of positive hydrogen ions produced is equal to the number of negative OH- produced.

Acids – any compound that forms H+ ions in a solution Acidic solutions contain higher concentrations of H+ ions than pure water and have a pH less than 7 Bases – a compound that produces OH- ions in a solution. Basic (alkaline) solutions contain lower concentrations of H+ ions than pure water and have a pH above 7.

W ATER ’ S UNIQUE PROPERTIES pH scale Indicates the concentration of H+ ions in a solution Goes from 0-14 Pure water = 7 7 = neutral List 3 acidic solutions. List 3 basic solutions.

W ATER ’ S UNIQUE PROPERTIES Buffer – weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH Helps to control pH Very important with body fluids in helping to maintain homeostasis.