Water and it’s importance

• Most important compound in living organisms.

• Life processes rely on free movement of molecules and ions.

• This occurs when substances are dissolved in water.

Water Molecule

Oxygen is slightly negative(more electronegative)

Hydrogen is slightly positive(less electronegative)

Neighboringmolecules held by a hydrogen bonds

Polarity of Water• Water is bonded together by polar covalent hydrogen

bonds.• Sharing is not equal; oxygen attracts electrons more

strongly than hydrogen• This gives water an assymetrical distribution of

charge. – Water can dissolve many substances

• Other polar molecules• Other charged molecules (positive and negative)

Water is a versatile solvent

• When water and another solution are mixed, you have an aqueous solution.

• Solute = what is being dissolved• Solvent = what is doing the dissolving• Polarity of water allows a variety of

substances to dissolve easily (ionic compounds and polar molecules)– Substances that repel water include non-polar and

non-ionic substances

Water as a solvent

• Polarity of water attracts other polar molecules – Ex: sugar

• These molecules are considered to be “hydrophilic” or water loving

• Molecules that are non-polar are repelled– Ex: oil

• Non-polar molecules are considered “hydrophobic” or water fearing

Importance to Living Things

• The chemistry of living things involves the study of solutions.

• Water is vital to life because the chemical reactions (metabolism) of living things must take place in aqueous solutions.

• This occurs when substances are dissolved in water.

• Life processes rely on free movement of molecules and ions. (ex: electrical signals in nervous systems)

Examples of aqueous solutions:

• Blood plasma – Liquid portion only

– Ions, larger molecules, gases all dissolved in water

• Cytosol– The gelatin-like aqueous solution inside cells.

• Interstitial fluid– Intercellular fluid of multicellular organisms

~11 L in average adult human body

• Aquarium water….

Temperature Stabilizer• Cells release heat as a result of metabolism

– Water helps to minimize temperature changes in cells

• Water can absorb great amount of heat before it’s temperature changes considerably– Due to hydrogen bonds– Energy disrupts hydrogen bonds rather than an increase in individual

molecules– Hydrogen bonds are constantly breaking and reforming

• This also allows large bodies of water and large organisms to regulate temperature– If bonds stay broken, water molecules at the surface escape into the

atmosphere

• Evaporation

• This takes away some energy and cools surface left behind

– This is why sweating cools you down!

High Specific Heat

Substance  C (J/g oC)

 Air  1.01

 Aluminum  0.902

 Copper  0.385

 Gold  0.129

 Iron  0.450

 Mercury  0.140

 NaCl  0.864

 Ice  2.03

 Water  4.18

• Water (liquid) has a high specific heat compared to other substances.

• It requires more heat to increase it’s temperature

• 0-100 degrees Celsius range!

Specific Heat Definiton:

• The quantity of heat required to raise the temperature of a substance by one degree Celsius is called the specific heat capacity of the substance.

Phase Changes

• High heat of fusion: Water loses a large amount of heat when it cools.

• High heat of vaporization: Water requires a LARGE amount of heat to change from a liquid to a gas

Phase Change Graph

Water is Cohesive• Cohesion- ability of molecules to stick together; results in

surface tension– Water attracts other water molecules, therefore forming

hydrogen bonds.– Hydrogen bonds are weak bonds – Hydrogen bonds help hold large molecules together-

such as protein.

• Cohesion examples:– Water bugs “walking on water”

Surface Tension• Cohesion allows water to form an interface

with a surface.

• Surface tension is the measure of how difficult it is to break this interface.

• Due to H bonding between water molecules

• Ex: materials are able to rest on water, provided the surface tension is not broken.

Adhesion• Sticking together of one substance to

another.

• Water is very adhesive; sticks to substances like glue.

• Capillary action is adhesion and cohesion in action.– Capillary action is the process of pulling water

up against gravity in plant vessels

Imbibition

• Process of soaking into a hydrophilic substance.

• Water soaking into seeds, paper towels, or sponge.

• Important for plants (seed germination usually requires imbibition)

Freezing and Expansion• Water expands below 4o C.

• Molecules are spaced further apart

• It is less dense, therefore ice floats in water.

• Ice at surface of lakes

and oceans provides a

thermal insulator for life

below the surface.