Properties of Water

• The hydrogen bonding in water contributes to the cohesion and adhesion of water molecules.
• Water's unique properties allow life to exist on Earth
• Most cells are surrounded by water
• Cells are about 70-95% water
• Water is a polar molecule
• A water molecule is a polar molecule with opposite ends of the molecule with opposite charges
• Oxygen is more electronegative, so the region around oxygen has a partial negative charge
• The regions near the hydrogen atoms have a partial positive charge
• Water is an excellent solvent
• Many compounds dissolve in water
• "Like dissolves like": Polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes
• Polar substances and nonpolar substances generally remain separate
• Ionic compounds readily dissociate (fall apart) into their component ions in aqueous solutions
• Life depends on hydrogen bonds in water
• Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms
• In a liquid, hydrogen bonds are constantly forming and reforming
• Hydrogen bonds occur between hydrogen and oxygen, nitrogen, and fluorine
• Hydrogen bonds are responsible for several important properties of water
• Cohesion: Water sticks together and forms films
• Surface Tension: Hydrogen Bonds contribute to surface tension
• Adhesion: Water is attracted to other polar molecules
• Dipole-Dipole Attractions: Capillary Action is a result of these attractions
• Water has a high specific heat
• Hydrogen bonds absorb a lot of energy
• Water temperatures don't change easily
• This property makes it easier to maintain homeostasis
• Water has a high freezing point
• Ice acts as an insulator to water below
• The Dissociation of Water Molecules (Chemical Buffer)
• Water does not exist as H2O, but often as a balance of H+, OH- (or H3O+)
• Changes in concentrations of hydrogen and hydroxide ions can affect the proteins and other molecules of a cell
• Adding certain solutes, called acids and bases, disrupts the equilibrium and modifies the concentrations of hydrogen and hydroxide ions
• The pH scale describes how acidic or basic a solution is
• A neutral solution has a pH of 7
• Equal balance of H+ and OH-
• Pure water has a pH of 7
• Some compounds form acids or bases
• An acid releases a hydrogen ion [H+] when it dissolves in water
• Acids have a high H+ concentration and a pH less than 7, making them more acidic
• A base removes hydrogen ions from a solution or forms H3O+ ions