Water

The Universal Solvent

• A water molecule is so small that there are billions of molecules in a single drop of water. About 60 million water molecules could be stretched side by side across a penny.

• Water is the ONLY compound that commonly exists in all 3 phases (solid, liquid, gas) naturally on Earth.

There would be no life on Earth without water.

• About 2/3 of the mass of a cell is made up of water, and most of the biochemical processes of life occur in aqueous solutions.

SOLVENT- the substance that does the dissolving. (liquid)

SOLUTE- the substance that is dissolved. (solid)

A large number of substances will dissolve in water.

Water is the universal solvent.

•Therefore, the water inside and outside of cells is able to carry nutrients into and around cells and wastes away from cells.

Water is a POLAR molecule

Polarity - the attraction of positive and negative electrical charges

OPPOSITES ATTRACT

Water Molecule

The Hydrogen side is slightly positive while the Oxygen side is slightly negative.

• One side of a water molecule is slightly negative (-) and the other side is slightly positive (+).

Positive hydrogen atom

Negative oxygen atom

H H

O

• Individual water molecules attract each other like magnets.

• In this way, water molecules

“stick together”.

+-

Cohesion: the tendency of two SIMILAR substances to stick together.

Adhesion: the tendency of two DIFFERENT substances to stick together, like water molecules stick to glass.

Capillary Action: the tendency of a liquid substance to move along the surface of a solid substance due to adhesion (as in water climbing a glass tube or inside a tree), even in spite of gravitational or other forces acting in the opposite direction

Transpiration

• Hydrolysis- a chemical reaction where water is involved.

• Hydrophilic- “water loving” can be dissolved in water, polar substances.

• Ex: Salt

• Hydrophobic- “water hating” cannot be dissolved in water, non-polar substances.

• Ex. fat, oil, soap

Like Dissolves Like

• High Specific Heat: water is able to absorb a large amount of heat energy before it changes temperature.– Specific heat: The amount of energy or

heat needed to change 1 gram water 1°C

Resistance to Temperature Change

• Water is a liquid from 0 ºC to 100 ºC

• Evaporative Cooling: water absorbs heat when it evaporates, allowing organisms to release excess heat.

• Heat of Vaporization: It takes a lot more heat for water to vaporize than just to raise its temperature a degree.– A function of changing states of matter

– True of boiling and evaporation

- As a result, lakes and oceans stabilize air and land temperatures.

• Large bodies of water can affect the climate.

High Surface Tension• Certain insects can walk on water because of its high surface tension.

•Polarity gives water its high surface tension through cohesion.

•Ex. Water strider

Solid expansionFor most substances, solids are more

dense than liquids. But the special properties of water make it less dense

as a solid - ice floats on water!

When water freezes, the water molecules line up, and as they do, they

move farther apart !

• The pH scale ranges from 0 to 14.

• The pH of pure water is 7.

• Substances added to water can lower or raise the pH.

• A solution with a pH above 7 is basic.

• A solution with a pH below 7 is acidic.

• Organisms can tolerate only small changes in pH because every cell has a particular pH at which it functions best.

• For example, changes in pH cause changes in the shapes of enzymes, resulting in a change in their activity.

Public Health

• In the past, streams and rivers were often used to dispose of human waste.

• These were called open sewers.

• This led to disease and contamination of drinking water.

•Advances in water treatment and sanitary sewers have helped to eliminate diseases from our waters.

Humans can live without food for more than two months, but cannot live for more than a week without water.

No =

• Clean, fresh water is essential for life.

• We must protect our water sources from pollution!!!!

Properties of Water Video

• http://dirpy.com/studio/0eNSnj4ZfZ8?q=properties%20of%20water

Fun Lecture Additions!

• pH video:– http://dirpy.com/studio/A_URRb5mk5Q?q=

acids%20and%20bases

• Mantis Shrimp comic strip:– Complements of one of your classmates!– http://theoatmeal.com/comics/mantis_shri

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