2 KEY CONCEPT Water’s unique properties allow life to exist on Earth.
3 Polar Molecule and Hydrogen bonds Water is a polar molecule.Polar molecules have slightly charged regions.OH_+Nonpolar molecules do not have charged regions.Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms.Because an oxygen nucleus has 8 protons and it pulls harder on the shared electrons than does Hydrogen with only 1 proton. Oxygen becomes slightly negative. Nonpolar share electrons more equally
4 Properties of waterLife depends on hydrogen bondsHydrogen bonds are responsible for three important properties of water.high specific heatcohesionadhesionWeak bond, but strong in numbers
5 Attraction between molecules of the same substance CohesionAttraction between molecules of the same substanceCaused by hydrogen bonding between water molecules
6 Water molecules on the surface stick together Surface TensionWater molecules on the surface stick togetherAttraction is fairly strongForms a “Film” at the surface
7 Attraction between molecules of different substances AdhesionAttraction between molecules of different substancesWater sticking to webPaint to wallsResults in Capillary action which allows water to climb structures
8 Amount of heat needed to raise or lower 1g of a substance 1° C. High Specific HeatAmount of heat needed to raise or lower 1g of a substance 1° C.Water resists temperature change, both for heating and cooling.Would you rather walk on sand or in water on a beach on a hot summer day?1
9 Water is Less Dense as a Solid Which is ice and which is water? 1
10 Solutions and Suspensions A solution is formed when one substance dissolves in another.Many compounds dissolve in waterA solution is a homogeneous mixture.Solvents dissolve other substances.Solutes dissolve in a solvent.solution
11 Ex bloodLiquid part plasma 95% water = SolventSolutes = sugars, proteins etc.
12 “Like dissolves like.”Polar solvents dissolve polar solutes.Dissolve because attraction between water and solute is greater than attraction between soluteIonic compounds (NaCl) dissolve because ions are attracted to water and water surrounds and rips apart moleculeNonpolar solvents dissolve nonpolar solutes.Polar substances and nonpolar substances generally remain separate.Ex “Oil and water don’t mix”
13 SuspensionsSubstances that don’t dissolve but separate into tiny pieces.
14 H2O H+ + OH- Acids, Bases and pH One water molecule is made of two ions, (H+) and Hydroxide Ion (OH-)Hydrogen Ion Hydroxide IonAcid BaseH2O H+ + OH-
15 The pH ScaleIndicates the percent of H+ ionsRanges from 0 – 14pH of 7 is neutralEach pH unit represents a factor of 10X change in concentrationpH 3 is 10 x 10 x 10 (1000x) stronger than a pH of 6
16 An acid releases a hydrogen ion when it dissolves in water. Acids, Bases and pHAn acid releases a hydrogen ion when it dissolves in water.high H+ concentrationpH less than 7more acidicstomach acid pH between 1 and 3
17 A base removes hydrogen ions from a solution. low H+ concentrationpH greater than 7bile pH between 8 and 9more basic
18 A neutral solution has a pH of 7. Buffers are weak acids and bases produced by the body to keep pH neutralMaintain homeostasisCan you think of a buffer to neutralize acid indigestion?pure water pH 7