Water - A Most Peculiar Substance

Water Water is so common that it’s easy to overlook its extraordinary properties. Water is actually a most unusual molecule, with physical and chemical properties found in no other material.

Importance of Water Water is the most abundant compound in nearly all living organisms. All living organisms require water more than any other substance. All organisms, in one way or another, are dependent upon water for survival.

Animation: Water Structure The Polarity of Water Due to an uneven distribution of electrons, water is slightly charged on each end. As a result, each water molecule exhibits polarity like a little magnet. Animation: Water Structure

Peculiarity of Water #1 Water is one of the few naturally occurring compounds that are liquids at the temperatures found on most of the Earth’s surface. This allows water to be successfully exploited by living things.

Peculiarity of Water #2 Most substances contract when they freeze, but water expands (ice floats on water). Many aquatic organisms are able to survive the winter due to this feature of water.

Peculiarity of Water #3 Because of the polarity of the water molecule, it is the greatest solvent in the world. Water molecules form “spheres of hydration” around dissolved substances.

Peculiarity of Water #4 Hydrogen bonds allow liquid water to show cohesive and adhesive behavior (stickiness). This “stickiness” is very important to organisms, especially plants.

Animation: Water Transport Cohesion & Adhesion Cohesion and adhesion of water molecules help in the transport of water against gravity in plants. Animation: Water Transport

Peculiarity of Water #5 Because of hydrogen bonding, water has a better ability to resist temperature change than most other substances. This property of water causes oceans and large lakes to moderate the temperatures of nearby land areas.

Effects of changes in pH Acids and Bases Acid: any substance that increases the H+ concentration of a solution Base: any substance that reduces the H+ concentration of a solution Biologists use the pH scale to describe how acidic or basic a solution is. Pure water [H+] = [OH-]

pH Scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Oven cleaner Household bleach Household ammonia Milk of magnesia Seawater Pure water Human blood Urine Rainwater Black coffee Tomato juice Vinegar, beer, wine, cola Digestive (stomach) juice, lemon juice Battery acid Neutral [H+] = [OH–] Increasingly Acidic [H+] > [OH–] Increasingly Basic [H+] < [OH–] The pH Scale The pH of a solution is determined by the relative concentration of hydrogen ions. Acidic solutions have pH values less than 7. Basic solutions have pH values greater than 7. Most biological fluids have pH values in the range of 6 to 8.

[10−7][10−7] = 10−14 [10−8][10−6] = 10−14 [10−9][10−5] = 10−14 [10−10][10−4] = 10−14 [10−11][10−3] = 10−14 [10−12][10−2] = 10−14 [10−13][10−1] = 10−14 [10−14][10−0] = 10−14 [10−6][10−8] = 10−14 [10−5][10−9] = 10−14 [10−4][10−10] = 10−14 [10−3][10−11] = 10−14 [10−2][10−12] = 10−14 [10−1][10−13] = 10−14 [10−0][10−14] = 10−14 The pH Scale Compresses the range of H+ and OH− concentrations by employing logarithms. The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration pH = −log[H+] [H+][OH−] = 10−14

Assignment Choose one of the 5 peculiarities of water and make a 8.5” X 11” poster representing this peculiarity. No words, letters, or numbers. Be creative and try to include examples or diagrams to help illustrate your points. Optional: Post a picture of your work to the blog.