The Extraordinary Properties of Water

The extraordinary properties of Water  A water molecule (H 2 O), is made up of three atoms: one oxygen (O) and two hydrogen (H). H H O

The extraordinary properties of Water The polarity of water is due to: –Polar covalent bonds –Uneven distribution of the electrons in the molecule:  The oxygen (O) end carries a slightly negative (-) charge.  and the hydrogen (H) ends carry a slightly positive (+) charge

The salt is held in solution by being surrounded by the water molecules

Universal Solvent  Water is called the “universal solvent” because more substances are known to dissolve in water than any other substance.  It is due to waters polarity.

Nonpolar and Polar  The difference between a polar (water) and nonpolar (ethane) molecule is due to the unequal sharing of electrons within the polar molecule.  Nonpolar molecules have electrons equally shared within their covalent bonds.  Therefore, nonpolar and polar molecules will not mix  Oil and Water!

The extraordinary properties of Water  What are they?

Cohesion Cohesion is the property of water that causes it to be attracted to itself. Surface tension, a measure of the strength of water’s surface, is the direct result of cohesion. The strong film on the surface of water is a result of the attraction between water molecules. This property allows insects to walk on the surface of water. It also allows creation of waves (which permits the diffusion of oxygen into lakes and seas).

Cohesion

Adhesion Water is not only attracted to itself, but will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. Water molecules will “tow” each other along when in a thin glass tube. This is called capillary action. This is the same process by which plants and trees remove nutrients from the soil, and paper towels soak up water..

Adhesion

Cohesion and Adhesion Together Creates the meniscus in the graduated cylinder Moves water up a tree

Because water molecules are so strongly attracted to each other, the temperature of water changes slowly. The large percentage of water in living things acts like an insulator, keeping the temperature constant. Causes winds on a local and global scale. High Specific Heat

 “Water vapor forms a kind of global ‘blanket’ which helps to keep the earth warm. Heat radiated from the sun-warmed surface ‘blanket’ which helps to keep the earth warm. Heat radiated from the sun-warmed surface of the earth is of the earth is absorbed and held absorbed and held by the vapor.” by the vapor.”

High Heat of Vaporization The heat of vaporization refers to the amount of energy required to convert 1g of water from a liquid to a gas. In order for water to evaporate, hydrogen bonds must be broken. As water evaporates, it removes a lot of heat with it. This allows organisms to cool themselves by evaporation (sweat)

Water is Less Dense as a Solid Ice is less dense as a solid than as a liquid and, therefore, floats on water. Bodies of water freeze from the top down. The floating ice provides insulation from extremely cold temperatures and allows living things to survive in the cold water under the ice.

Water is Less Dense as a Solid WaterIce

Importance to Biology  Homeostasis  Constant physiological condition of cells, organisms, global ecosystems –a. Makes a good insulator –b. Allows for separation of areas –c. Universal solvent (polarity) –d. Coolant (sweat) –e. Ice protects against temperature extremes –f. Most abundant compound in living things!!

pH: A look at Acids and Bases  An acid is a substance that increases the concentration of hydrogen ions (H+) in water or donates a proton.  A base is a substance that decreases the concentration of hydrogen ions, in other words, increasing the concentration of hydroxide ions OH- or accepts a proton.

What is pH?  The pH scale ranges from 0 on the acidic end to 14 on the basic end, a solution is neutral if its pH is 7.  At pH 7, water contains equal concentrations of H+ and OH- ions. –Substances with a pH less than 7 are acidic –Substances with a pH higher than 7 are basic –The pH scale is a log scale so a change of one pH unit means a 10x change in the concentration of hydrogen ions. –The pH scale is a log scale so a change of one pH unit means a 10x change in the concentration of hydrogen ions.

pH Scale

Biological Importance  Living things are extremely sensitive to pH and function best when solutions are nearly neutral (some exceptions). Most living matter has a pH of about 7.2.  Living things are extremely sensitive to pH and function best when solutions are nearly neutral (some exceptions). Most living matter has a pH of about 7.2.  Water's ability to accept, carry and release protons in acid-base reactions is another of its chemical properties that makes it very suitable as a biological medium.  Water's ability to accept, carry and release protons in acid-base reactions is another of its chemical properties that makes it very suitable as a biological medium.