1. Properties of Water

2. First of all…what’s up with water?
Did you know…
Life began in water
Percentage of earth covered in water:
About 75%
Your cells are approximately this percentage water:
70-95%

3. Hydrogen Bonds in Water
Hydrogen bonding is a dynamic process
Weak bonds
This is a constant process of making and breaking
H-bonds are made and broken in the tiniest fraction of a second

4. The Water Molecule
Is a polar molecule
Has a – and + end

5. Properties of Water
The unique structure of water gives it seven special properties
H-bonds between water molecules
Polarity

6. 1. Water is a powerful solvent
Dissolves other polar substances
Polar substances are hydrophilic
“water – loving”
Non-polar substances are hydrophobic
“water – hating”
Able to dissolve polar compounds (solutes)
Separates ionic substances
Many covalent compounds are hydrophilic due to their polar regions
Non-polar compounds are hydrophobic
Soap is amphipathic – it has hydrophilic and hydrophobic ends

7. 2. Water is wet Due to two properties:
Adhesion: Attraction between water and other types of molecules
Cohesion: Attraction between water and water
This means that water can stick to itself and to other substances
Capillary action in plants! – water rises against gravity to leaves

8. 3. Water has a high surface tension
This is due to water's attraction to itself
Water molecules are more attracted to each other than to the air
This attraction is due to H-bonds
This allows a “bump” of water to form on overfilled glasses

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10. 4. Water has a high specific heat
Takes a lot of energy to heat up water or cool it down
Water will absorb a lot of heat with a relatively small increase in temperature
There are two “types” of energy
Kinetic energy
Potential energy
Temperature is a measure of the amount of kinetic energy in a system
Heat is measured in calories
A calorie is the amount of heat it takes to increase the temperature of 1 gram of water by 1°C
Ex: water during the day cooler than land. Water during the night warmer than land – cities near bodies of water have more moderate temperatures
Water in a pond will stay relatively the same temperature form day to day

11. 5. Water has a high boiling point
A large amount of energy is required to break the H-bonds in order to change water from a liquid to a gas
As temp. increases, the water molecules move faster and faster until they are moving so fast that H-bonds are not allowed to form
At this point, water molecules are lost to the air as water vapor

12. 6. Water is a good evaporative coolant
Because it takes a lot of energy to turn water from a liquid to a gas, when water evaporates, a lot of energy leaves with it
When we sweat, the water absorbs energy (heat) from our bodies until enough energy is absorbed to evaporate the sweat, in turn removing the heat

13. 7. Water has a high freezing point & a higher density as a liquid than a solid
Maximum density of water is at 4°C
Freezes at 0°C
As the temp approaches 0°C, the process of breaking H-bonds slows
When water freezes, H-bonds no longer break and each water molecules is bonded to 4 other water molecules
Water is now locked into a crystal structure (ice)
The H-bonds keep the molecules far enough apart to make ice less dense than liquid water
Ice floats!
This is important because floating ice slows the freezing process of water by insulating the water underneath, which moderates temperatures on earth

14. Questions – quick write (5 min) and discuss with partner (3 min)
What is water? How would you describe water chemically?
List a physical property of water and one reason why this property helps water support life on earth.