Properties of Water

Properties of Water Water appears very ordinary and common. It’s nearly everywhere. But it possesses the most unusual properties!! In fact, it’s quite weird and definitely wonderful.

Polarity I. Most properties of water (H2O) are due to it being a polar molecule.   Polar means that one side of the molecule has a positive charge and one side has a negative charge (kind of like a magnet)                                                                   

Polarity Because of polarity, water can form weak hydrogen bonds with other water molecules (this is how raindrops form). These shift constantly, yet the holding power is very great.

Universal Solvent II. Universal Solvent: Disappearing Act With enough time nearly everything will dissolve in water somewhat. This is important because for chemical reactions to occur in living creatures, molecules must dissolve in the water in our bodies.

Cohesion III. Cohesion - water molecules stick to each other by weak hydrogen bonds. How many water drops fit on a penny? Why? Water sticking together is important to living systems. For example - for water to be able to move in a tiny column from the soil to the roots and leaves of a plant, it must stick together.                                                        

Adhesion IV. Adhesion- water sticking to or “wetting” other substances. This is important because it keeps our inside surfaces wet and it removes the friction of internal body parts when moving.

Resistance to Temperature Change V. Resistance to Temperature change  It takes more heat input to cause water to rise in temperature than almost any other substance. (this is also true for heat loss) The high water content of plants and animals helps them to retain a relatively constant internal temp. This is critical for chemical reactions to occur.

Density VI. Density - the amount of matter in a certain volume. (d=m/v)   In most liquids density increases as temp drops. But water is different. It starts expanding when the temperature gets really cold (ex 39 °F) so that ice is lighter than water - very weird!!

Density This is important to life because lakes freeze from the surface. If lakes froze from the bottom the ice there would never melt. The ice on the surface protects or insulates the organisms in the water underneath

Transparency VII. Transparency - not due to polarity Water is clear This is important for the transmission of light so that aquatic plants have light to carry out photosynthesis and so that animals in the surface water can see.

Properties of Water WATER PROPERTIES ARE WEIRD AND WONDERFUL. WATER MAKES LIFE AS WE KNOW IT POSSIBLE.

Reflection Questions 1. What was the main purpose of these notes? 2. What is polarity? 3. Draw a water molecule and label the atoms and charges on the molecule. 4. What is density? 5. Choose a property of water and describe why it is important. 6. Write Your Own (write your own question from the notes and answer it)