Water Why is water so important to life?

 Water covers more than 75% of the Earth’s surface.  Living organisms are composed of 60-90% water.  Life is dependent on water.

Oxygen (-) Hydrogen (+) Hydrogen (+) Let’s Review

Water Has Unique Properties  Cohesion makes it a group effort  Adhesion makes it a sticky situation  Surface tension makes it hard

Water helps makes the Earth bearable  High specific heat- it’s a heat sink  High heat of vaporization  High heat of fusion

Water is the universal solvent Hydrophilic molecules are attracted to water and can be dissolved by water. Hydrophilic molecules are attracted to water and can be dissolved by water. Ex. Proteins, salts, and sugars Ex. Proteins, salts, and sugars

Ex. Saltwater Ex. Saltwater

Hydrophobic molecules repel water and therefore cannot be dissolved by water. Hydrophobic molecules repel water and therefore cannot be dissolved by water. Ex. Oil Ex. Oil

Ionization of Water - water breaks apart into hydrogen and hydroxide ions Ionization of Water - water breaks apart into hydrogen and hydroxide ions  Pure water breaks apart into equal numbers of these ions

Some substances do not release equal numbers of H + and OH -. What are they? Acids and Bases  Acids are substances that release H ions into solution when they disassociate Ex. HCl H + + Cl -  Acids taste sour Ex. Vinegar or Lemon juice Ex. Vinegar or Lemon juice

 Bases are substances that accept H ions Ex. NaOH Na + + OH - Two examples of how bases do this Ex. NH 3 + H + NH 4  Bases are slippery Ex. Bleach or Soap Ex. Bleach or Soap How can we determine the acidity of a solution?

pH Scale pH measures the concentration of H ions of a substance

So, why is pure water neutral? It ionizes into equal parts of H and OH ions Why is pH important to life? Organisms must maintain the pH of their bodies within a normal range (homeostasis) Ex. blood pH or stomach pH

How could organisms prevent pH from fluctuating dramatically? Buffers are chemicals that minimize the fluctuation of pH by either accepting H ions or releasing them. Ex. Carbonic Acid (weak acid, pH = 6.4) Serves as a buffer for our blood Serves as a buffer for our blood