Water PropertiesSC.912.L.18.12

Water has unique properties that make it an important substance for

life.

Cohesion and Adhesion

Hkhkhjhkjhkh Cohesion is an attraction between substances of the same kind. Example: Hydrogen bonds between water molecules cause the cohesionof liquid water. Because of cohesion, water andother liquids form thin films and drops.

Adhesion• Adhesion is an attraction • between different substances.• Water molecules are attracted• to many other similarly polarized • substances• Example: Adhesion powers• capillary action, where H20 • molecules move upward thru• a narrow tube, such as the stem • of a plant.

Stores Heat Energy

• Water absorbs heat • more slowly and • retains this energy• longer than many other substances do. Many organisms releaseexcess heat through water evaporation.Example: Humans cool themselves by sweating.The water vapor lost through the evaporation of sweat carries heat away from the body.

Universal Solvent• Water has the ability to • dissolve many substances.• The polarity of water• enables many substancesto dissolve in water. Example: Ionic compounds and polar molecules dissolve best in water

Surface Tension• Water molecules• like to cling to one• another. At the • surface, there arefewer water molecules to cling since there is airabove (no water molecules). This results in a stronger bond between those molecules that actually do come in contact with one another and a layer of strongly bonded water.Example: Small insects such as the water strider can walk on water because their weight is not enough to penetratethe surface.

Review Questions:

Why is water a good solvent for many ionic compounds?

Water has the ability to store heat longer than other substances. What benefit does this property of water provide to organisms?