1. Properties of Water
Section 2.5

2. Learning Objectives
Explain how hydrogen bonds between adjacent (neighboring) water molecules govern many of the properties of water.
Explain how water is important to biological systems.

3. Importance of Water in Biological Systems
Most of the mass of organisms is from water
In photosynthesis water is the source of the oxygen released by plants
Water is the solvent for most biological reactions
Water is a reactant or product in many chemical reactions in organisms
Many organisms live in water or depend on the availability of clean water

4. Hydrogen Bonds Form between water molecules
Because water is polar
Hydrogen of one water molecule forms a hydrogen bond with the oxygen of a neighboring water molecule
One water molecule can form 4 hydrogen bonds

5. Water Has Unique Properties
Due to its ability to easily form hydrogen bonds
Cohesion
Adhesion
High Specific Heat
Less Dense as a Solid
Excellent Solvent

6. Cohesion Cohesion = Molecules being attracted to each other
Water molecules form hydrogen bonds with other water molecules

7. Adhesion
Adhesion = molecules are attracted to other types of molecules
Water molecules are attracted to the sides of a glass

8. Capillary Action
Cohesion & Adhesion work together to pull water up a small tube
Adhesion between water & surface of tube pulls the first water molecule up the tube
Cohesion between water molecules pulls the rest of the water molecules up behind the first one

9. Capillary Action

10. Surface Tension Water has a high surface tension
Surface Tension = the attraction that molecules at the surface of a liquid have for each other
Allows some organisms to walk on water

11. Hydrophilic Substances Dissolve in Water
Hydrophilic = water loving
Hydrophobic = water fearing
To dissolve a hydrophilic substance water molecules form hydrogen bonds with the polar molecule or the ion
Water molecules surround the polar molecule and ions & prevent them from forming bonds with other molecules

12. Polar Molecules & Ionic Molecules Dissolve in Water

13. Water Helps Maintain a Stable Temperature
Kinetic Energy = energy of movement
Heat = Total kinetic energy that is not usable to do work
Temperature = average kinetic energy

14. Water has a high heat of vaporization & a high specific heat
Heat of Vaporization = the amount of kinetic energy required for a water molecule to change from liquid to gas
Specific Heat = the amount of kinetic energy required for 1 g of water to increase by 1 °C

15. Water requires a large amount of energy to increase in temperature & evaporate
Because it can form so many hydrogen bonds
It is hard to break all the hydrogen bonds & free one water molecule before new hydrogen bonds form

16. Results… Water takes a long time to heat up compared to land
Land surrounded by water stays cooler than land surrounded by land
When you sweat it actually cools you down
Water evaporating takes a lot of heat with it, leaving less heat behind than you had before

18. Ice Floats Most solids are more dense than their liquid form
Not Water!
Hydrogen bonds hold water molecules apart & as a solid the space is “frozen”
Ice is less dense than liquid water
Water is densest at 4°C

19. Allows organisms to live in water
If ice was more dense than eventually all liquid water at Earth’s surface would freeze in cold areas