Water and Life

•The Molecule That Supports LifeWater is the biological medium

¾ of the Earth is covered by water

Living cells require water and are made up of 70-95% water

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Exists in all 3 phases naturally on EarthItem 2

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Life began in water over 3 billion years ago

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Intramolecular force: polar covalent bond – unequal electron sharing

The overall molecule is also polar – overall distribution of electrons is unequal.

Intermolecular force: Hydrogen bonds the slightly negative O of one water molecule attract the slightly positive H ends of neighboring water molecules.

4 H bonds per molecule! Last for trillionths of a secondSheer quantity implies many bonds at a given time.

•Water is Made of Polar Covalent Bonds

• H bonds keep water molecules linked creating a more structured liquid than most.

• This phenomenon is know as cohesion

• Cohesion helps drive water transport in plants

• Adhesion – the attraction between 2 different substances also helps (water to cells)

• Water also has a high surface tension!

•Cohesion of Water MoleculesA second line of text here

• Water can absorbs and store heat from the air

• Water has a very high Specific Heat relative to other substances. 1cal/g×°C

• Means it takes a great deal of energy to change the temperature of water!

• What are some of the impacts on life of this specific heat?

•Water Moderates Temperature

• Water also has a high heat of vaporization (energy needed to convert 1g of liquid to gas).

• Regulates temperature stability of bodies of water.

• “hottest” molecules vaporize first – leaving the remaining surface slightly cooler.

•Evaporative Cooling

•Density of Water vs. IceLiquid water is more dense than solid water

This is directly caused by the hydrogen bonding of water.

Above 4°C water behaves like most liquids.From 4-0°C water starts to freeze due to lack of movement.0°C locked in crystalline lattice.

Water can dissolve Ionic bonds due to the positive and negative regions of the molecule.

As long as a molecule has a polar region the water can generate H bonds with it.

Hydrophobic: Water-fearing. Non-ionic and Non-polar. Do not mix with water!

Hydrophilic: Water-loving. Does not need to dissolve, but will generate bonds with the water.

•Water: The Solvent of Life

•Solubility: Dissolving and Solutions

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•Water is a Polar Covalent Solvent

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ACID

• Acids increase H ions in a solution.

• Acids increase the pH

• Bases reduce H ions concentrations.

• Bases decrease the pH

BASE

•Water as an Acid or BaseWater is amphoteric

pH measures the negative log of the hydrogen ion concentration.

• Most living things require an optimal pH of 7 (neutral).

• A buffer is a substance that minimizes changes in H and OH concentrations.

•Water is a Buffer

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