What is the importance of hydrogen bonding? How do compounds dissolve in water?

 Water is polar ◦ The oxygen atom has a stronger attraction for electrons than hydrogen ◦ Oxygen pulls electrons closer – gains slight negative charge ◦ Electrons are pulled away from hydrogen- slight positive charge -Balloon Demo

 Opposite charges of polar molecules can interact to form hydrogen bonds

 Cohesion – water molecules bond to each other (Bonds to Itself) ◦ Surface tension  Adhesion – water molecules stick to other polar molecules (Bonds to Other Things) ◦ Capillary action (Yarn Tight Rope)  High specific heat – water resists a change in temperature (Stores Heat) (H20 vs Alcohol)  Less dense when it freezes ◦ Most dense at 4 o C

 Solute – substance that is being dissolved  Solvent – substance that dissolves another substance  Ionic and other polar compounds are broken apart by the slight charges on the water molecule

 Acid – compound that releases H+ into solutions  Base – compound that removes H+ from solutions  A solutions H + concentration is measured on the pH scale ◦ Ranges from 0 to 14 ◦ Acids – 0 to 6; H + > OH - ◦ Neutral – 7; H + = OH - ◦ Bases – 8 to 14; H + < OH -

 pH is regulated in organisms by substances called buffers ◦ Buffers can remove H+ or add H+ to solutions to adjust pH ◦ This maintains homeostasis  Human blood should be at a pH of 7.4, if it goes down to 7.0 or up to 7.8 then it is lethal