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Properties of Water.

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Presentation on theme: "Properties of Water."— Presentation transcript:

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.

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