LIFE DEPENDS ON THE UNIQUE PROPERITIES OF WATER

Questions to think about

• Why do put salt on the roads? • Why do we salt a pot of pasta water? • At a higher altitude why must we

cook “boil” something longer?

• Cells are 70% to 95% water

Human Composition

Plant Composition

• As much as 95% plants can be made of water

Formula and Bonds

Formula: H2OBonds: Covalent- electrons are shared between Oxygen and Hydrogen

Because Oxygen has 8 Protons (+) it pulls the electrons more (Electron HOG)

Oxygen acts Negative- Hydrogen acts Positive

HH

O

How do we get Hydrogen Bonds?

Hydrogen Bonds

• Hydrogen Bonds- weak bondsslightly positive H is attracted to the slightly negative O of another water molecule

Polarity • Polar molecule:

molecule in which opposite ends have opposite electric charges

• Why? Water is a polar molecule: because Oxygen is an electron HOG

• POLAR COVALENT BOND

The polar nature of water and the effects of hydrogen bonding explain most of water's unique properties.

• Cohesion • Adhesion• Solubility • Temperature moderation• The lower density of ice

Cohesion • Water “sticks” to each

other because of hydrogen bonds

• Surface tension

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over-filled water

3oz Dixie cup

Jesus Christ Lizard

Adhesion

• Water molecules are also attracted to certain other molecules.

• Ex. In trees/plants water goes against gravity

Called capillary action

Water is the a Universal Solvent

Water is able to dissolve other Polar & ionic compounds when mixed by causing the ions to break away and surround them.• Water dissolves Salt (Na+Cl-)

Water (Polar) will not dissolve (Nonpolar)

• Like dissolve Like

• Water won’t dissolve oils

Temperature and Water

• When you heat molecules move faster

• When you cool molecules move slower

• Water takes more energy to heat because energy must break hydrogen bonds

Boiling Point: 100 oC 212 oF

Does water boil faster if you add salt to it?

• Water Boils when it has enough energy for the molecules to leave

Freezing Point

• What would happen if our oceans did not have salt in them?

• Why do we put salt on our roads?

• Why at effect does salt have on FREEZING POINT?

0 oC or 32 oF

LOW DENSITY OF ICE• Density- amount of matter

in a volume

• In most substances the solid state is more dense than the liquid state

• Water is the oppositeICE IS LESS DENSE THAN WATER and will FLOAT

LOW DENSITY OF ICE

• WHY?????• Hydrogen

bonds in ice (solid) keep molecules spaced out

LOW DENSITY OF ICE

• Floats • Ice insulates the

liquid water below allowing life to persist

Homework Questions 1. Explain how the structure of water molecules results in

attractions among them.

2. Give an example of how cohesion among water molecules is important to living things.

4. Name three conditions on Earth that make the planet suitable for life.5. Explain one way in which water can moderate temperature.

Does water boil faster if you add salt to it?

• Water Boils when it has enough energy for the molecules to leave

•Why do we need salt in our ice, when making ice cream? Watch Video

• Salt Decreases the freezing point

What would happen if our oceans did not have salt in them?

Why is this important for life?

Water Boiling Point Ethanol Boiling Point