Chapter 2 2.2 – Properties of Water

2.2 – Properties of Water Water (H2O) is a polar molecule Polar – Unequal distribution of charge Hydrogen side is slightly + Oxygen side is slightly – Hydrogen Bonding – the force of attraction between a hydrogen with a slightly + charge to another atom with a slightly - charge Water’s unequal charge allows it to form hydrogen bonds and gives water its unique properties

2.2 – Properties of Water Properties of Water Cohesion – attraction between like molecules Hydrogen bonds between water molecules produces surface tension Biological membranes Adhesion – attraction between unlike molecules Hydrogen bonds between water and other atoms allows water to dissolve many different substances Water = the solvent of life Adhesion and cohesion of water lead to capillary action Heat Capacity – ability to resist a change in temperature Hydrogen bonding between water molecules requires more energy than normal to cause a change in water temperature

Solvent Versatility as a Solvent for a variety of solutes Due to water’s polarity, it is an excellent solvent Water readily forms hydrogen bonds with ionic compounds By doing so, water forms a hydration shell around these molecules causing them to dissolve in solution

2.2 – Properties of Water Acids, Bases and pH In some cases, certain substances dissolve in water and give off reactive ions Acid – a substance, that when dissolved in water, gives off hydrogen ions (H+) Base – a substance, that when dissolved in water, gives off hydroxide ions (OH-)

2.2 – Properties of Water Acids, Bases and pH (cont.) The strength of an acid or base depends on how much H+ or OH- is given off Measured using the pH scale pH 7 = neutral pH from 0-6.9 = acidic pH from 7.1-14 = basic (alkaline) Buffer maintain homeostasis in organisms. weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH.