2.2 Properties of Water KEY CONCEPT Water’s unique properties allow life to exist on Earth.

2.2 Properties of Water O HH _ ++ Life depends on hydrogen bonds in water. Water is a polar molecule. –Polarity – characteristic of molecules that have unequal sharing of electrons and therefore develop partial positive and negative charge regions –Polar molecules have slightly charged regions. – Nonpolar molecules do not have charged regions. – Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms. –Type of intermolecular force – attraction between two different molecules

2.2 Properties of Water Hydrogen bonds are responsible for three important properties of water. –high specific heat –cohesion –adhesion

2.2 Properties of Water Cohesion, Adhesion and Capillary Action Cohesion – attraction of a molecule to another molecule of the same substance –Causes surface tension in water Adhesion – attraction of a molecule to a molecule of a different substance –In combination with adhesion, causes capillary action Capillary action –Movement of a substance through tiny tubes against the force of gravity due to cohesion and adhesion

2.2 Properties of Water Specific Heat and Density of Water Specific Heat –The amount of heat energy needed to raise the temperature of 1 gram of a substance 1 degree Celsius –Water has a high specific heat Density –Mass to volume ratio –Water is most dense at 4 degrees Celsius -This is why ice floats -Unusual for a solid form to be less dense than a liquid form of the same substance

2.2 Properties of Water Many compounds dissolve in water. A solution is formed when one substance dissolves in another. –A solution is a homogeneous mixture. –Solvents dissolve other substances. –Solutes dissolve in a solvent. solution

2.2 Properties of Water “Like dissolves like.” –Polar solvents dissolve polar solutes. –Nonpolar solvents dissolve nonpolar solutes. –Polar substances and nonpolar substances generally remain separate.

2.2 Properties of Water Some compounds form acids or bases. An acid releases a hydrogen ion when it dissolves in water. –high H + concentration –pH less than 7 more acidic stomach acid pH between 1 and 3

2.2 Properties of Water A base removes hydrogen ions from a solution. –low H + concentration –pH greater than 7 bile pH between 8 and 9 more basic

2.2 Properties of Water A neutral solution has a pH of 7. pure water pH 7