Properties of Water

Hydrogen Bonds  Hydrogen bonds do not join atoms … Hydrogen bonds are attractions between compounds

WATER

WATER Activity: (5 minutes) Create the structure of water, including the hydrogen bonds between molecules (drawing, model, skit)

Hydrogen Bonds Give Water Unique Properties (Part I)  Heat Storage A large input of thermal energy is required to disrupt the organization of liquid water This minimizes temperature changes High Heat of Vaporization At high temperatures, hydrogen bonds do break Water is changed into vapor resulting in a cooling effect

Heat Storage & High Heat of Vaporization  Water’s heat storage ability keeps temp of coastal areas more stable!

Properties of Water Heat Storage & High Heat of Vaporization These properties allow water to trap lots of heat and take it away by evaporative cooling, like when you sweat! Ahhhhh …

Questions to Ponder (Think, Pair, Share) Where would you feel cooler on a 100 degree day: Las Vegas or Leesburg? Why? Why do athletes like polyester more than cotton? Where and why was Gatorade developed? Why does it seldom (if ever) snow in San Francisco, even though it is similar in latitude to Leesburg?

Ice Formation  At low temperatures, hydrogen bonds don’t break Water forms a regular crystal structure that floats

Ice is less dense than water, so ice floats!  This is super important because it prevents bodies of water from freezing solid and killing all life on the surface and underneath!

Question to Ponder Think-pair-share  At what temperature is the ice cover? Estimate the temperature of the “blue water”. Which layers are warmer? Which are colder?

Hydrogen Bonds Give Water Unique Properties (Part II)  Hydrogen Bonds Give Water Unique Properties (Part II) Water strider Cohesion Attraction of water molecules to other water molecules Example: Surface tension Adhesion Attraction of water molecules to other polar molecules Example: Capillary action

 Surface Tension! Cohesion (water to water) makes the surface of water like a “solid” film!

 Surface Tension! Demonstration

Capillary Action!  Cohesion and Adhesion Allows for Transpiration - The movement of water up a plant (by “capillary action”) because of pull from evaporation through the leaves.

 Capillary Action! demonstration

Question to Ponder Think-pair-share  Question to Ponder Think-pair-share Why does it hurt more to dive into the pool “spread eagle” (belly flop) than to dive in head first, and why? Which is easier to siphon, water or diesel fuel, and why?

Water is a Great Solvent: Hydrophilic & Hydrophobic Substances  Hydrophilic (“water-loving”) substances Polar Hydrogen bond with water Example: sugar Hydrophobic (“water-fearing”) substances Nonpolar Repelled by water Example: oil

Water is a Great Solvent: Hydrophilic & Hydrophobic Substances  demostration

Solute + Solvent = Solution  Solution Solute + Solvent = Solution  Solute- solid particles that dissolve Solvent- what causes dissolving Solution- homogenous mixture made from solute and solvent Concentrated: when there is more solute than solvent Diluted: when there is more solvent than solute

Solute + Solvent = Solution  Solution Solute + Solvent = Solution  demonstration

0---------------------7-------------------14 The pH Scale  Measures H+ concentration of fluid Change of 1 on scale means 10X change in H+ concentration Highest H+ Lowest H+ 0---------------------7-------------------14 Acidic Neutral Basic BUFFERS Buffers are substances that resist pH changes! 

Acids & Bases  Acids These substances cause water to release its H+ Acidic solutions have pH < 7 Bases These substances grab H+ from water, leaving behind OH- ions Basic solutions have pH > 7