Water

The Universal Solvent

OBJECTIVE:

TSW understand the chemical and biochemical principles essential for life.

Key concepts include-

• water chemistry and its impact on life processes.

Review

• Elements are made up of atoms

•Compounds are made up of molecules.

• A 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.

After Lab

• Water is the ONLY compound that commonly exists in all 3 phases (solid, liquid, gas) 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 water 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

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

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

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.

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

•Amphipathic- molecules which have a region of each. Ex. Detergents that interact with each

Like Dissolves Like

• 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”

+-

• Water has a high specific heat capacity

• i.e. (id est ~ that is) Water is able to absorb a large amount of heat energy before it changes temperature.

• It also means it is very slow in giving that thermal energy up

Resistance to Temperature Change

• Water is a liquid from 0 ºC to 100 ºC

• Water absorbs heat when it evaporates, allowing organisms to

release excess heat.

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

• Large bodies of water can affect the climate.

High Surface Tension• Polarity and cohesion give water its high surface tension.

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

•Ex. Water strider

Solid Expansion• For 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!

• Ice floats because hydrogen bonds hold water molecules farther apart in a solid than in a liquid

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 human waste.

Current Sewer System Designs

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

No =

“Now that’s some high quality…”

• Clean, fresh water is essential for life.

• We must protect our water sources from pollution!