Properties of Water Biology 1 Mr. Spoor

1. Water is the Universal Solvent It can dissolve many substances, like nutrients and wastes. Negative ion attracts positive pole of water Positive ion attracts negative pole of water

2. Water has polarity This means that one side of the molecule is positive, one side is negative.

3. Water has Polar Covalent Bonds - Negative Pole Covalent Bond Covalent Bond O H H + + Positive Pole Shared electrons (which are negative) spend more time around the O (oxygen). This makes the O side of water slightly (-) and H’s slightly (+).

**Draw this in your notes** 4. One water molecule is attracted to other water molecules by hydrogen bonds. + + - Hydrogen Bonds + - + - **Draw this in your notes** + + - + + + - +

Water’s Polarity and its Ability to Form Hydrogen Bonds: gives water unique properties which make water very important on Earth

Since water is polar and can form hydrogen bonds: a. Water molecules are attracted to other water molecules by COHESION – the attraction between molecules of the same substance b. Water molecules are attracted to other polar molecules by ADHESION – the attraction between molecules of different substances

5. Exhibits Surface Tension Water molecules stick together (cohesion) on surface of water This allows the water strider to walk on water.

6. Capillary Action Water can climb thin tubes. Water is able to climb from roots all the way up to leaves at the top of a tree Adhesion to the roots Cohesion to neighboring water molecules, pulling them along.

7. Resistance to Changes of Temperature Water can absorb a lot of heat without getting hot, and can lose a lot of heat without getting cold.

Resistance to temperature change allows organisms to maintain constant body temperature, AND keeps the Earth at a fairly constant temperature. Remember – about 2/3 of Earth is covered with water, and up to 60% of a human’s weight is water!

8. High Heat of Vaporization It takes a lot of heat energy to change liquid water to water vapor, because hydrogen bonds must be broken. Evaporation of sweat takes heat energy from the body, allowing sweat to cool us.

9. Expands as it freezes Hydrogen bonds lock into place, and push water molecules farther apart. Ice is less dense than water

Low Density- Importance of Expansion upon Freezing Ice Floats! Life at the bottom of lakes does not get crushed Ice also serves as an insulator Ice breaks rocks into soil

So why is water so important? Almost every solution is made of water. Acids and bases are made of water We are mostly water.