NOTES FOR BIOLOGY 1201

Section 001

Spring 2005

DR. STEVEN POMARICO

Water: Hydrogen Bonding, Solubility, and Specific Heat - 2.3.1

Cells are 70-95% water.

Water cover 70% of the earth’s surface.

>>>>>Some of the most biologically important polar covalent bonds are the bonds in water molecules.

          Because of these polar covalent bonds water is a polar molecule.

                     This is an example of an emergent property.

The polarity of water molecules makes water a good solvent for molecules that have charged regions (i.e. polar molecules) or atoms that are charged (i.e. ions)

Water is a very versatile solvent.

---Solution

---Solvent

---Solute

---aqueous solution

Water's polarity along with hydrogen bonding orders water into a higher level of structural order.

This higher structural order and polarity results in some other extraordinary emergent properties:

Water resists changes in temperature because of high specific heat.

>>>>>>This helps to moderate the effects of changes in temperature. 

---Heat

---Kinetic energy

---Temperature

---Celsius scale

---Calorie (cal)

---Kilocalorie (kcal or Cal)

---Specific heat

Water has a high heat of vaporization and cools surfaces as it evaporates.

---Vaporization (evaporation)

---Heat of vaporization

---Evaporative cooling

Water: Adhesion, Cohesion, and a Solid That Floats - 2.3.2

Water molecules have “sticky” emergent properties including: cohesion, adhesion, and surface tension.

---Cohesion

---Adhesion

---Surface tension

Water expands when it freezes.

This causes ice to float and helps insulate the water below the ice from lower temperatures which may occur above the ice

Water: Hydrophilic and Hydrophobic Substances - 2.3.3

Nonpolar substances are hydrophobic.

---Hydrophobic

Polar and ionic substances are hydrophilic.

---Hydrophilic

>>>>>>Two of the most important factors of biological solutions are: solute concentration and the degree of acidity.

---Solute concentration

One of the most often used measures of solution concentration is molarity.

---Molarity

---Mole

---Molecular weight

Dissociation of Water and the pH Scale - 2.3.4

Water molecules can dissociate. That means that the hydrogen atom of one water molecule leaves an electron behind, and joins with another water molecule as a hydrogen ion.

---Hydrogen ion (H⁺)

---Hydronium ion (H₃O⁺).

---Hydroxide ion (OH^-).

ACIDS AND BASES

At equilibrium in pure water at 25 ^oC

          -the number of H⁺ atoms = the number of OH^- atoms

          -the molar concentration of H⁺ = [H⁺] = 10^-7 M

                     Moles H⁺/liter of solution

---Acid

---Base

          For a neutral solution [H⁺]=[OH^-]

          For an acidic solution [H⁺]>[OH^-]

          For a basic solution [H⁺]<[OH^-]

Strong acids and bases dissociate completely in water

                     Examples: HCl and NaOH

Weak acids and bases dissociate only partially in water

                     Examples: H₂CO₃ (carbonic acid) and NH₃

>>>>>>pH Scale

In any aqueous solution [H⁺][OH^-]=10^-14

          For a neutral solution [H⁺]=10^-7 and [OH^-]=10^-7

          For an acidic solution [H⁺]=10^-5 and [OH^-]=10^-9

          For a basic solution [H⁺]=10^-9 and [OH^-]=10^-5

---pH scale

---pH

          For a neutral solution [H⁺]=10^-7 and pH =7

          For an acidic solution [H+]=10^-5 and pH =5

          For a basic solution [H+]=10^-9 and pH = 9

Hemoglobin as a Buffer - 2.3.5

>>>>>>Buffers

---Buffers

          Buffers are combinations of H⁺ donor and H⁺ acceptor forms of weak acids                      or bases.

          Buffers function by accepting H⁺ ions from solution when they are in excess,

                     and donating H⁺ ions to the solution when the supply is depleted.

          Example: Bicarbonate buffer

>>>>>>Acid Precipitation and the threat to the environment

---Acid Precipitation

-Found as low as pH 1.5

-Formed by the interaction of atmospheric sulfur oxides and nitrogen oxides with water vapor. Interaction results in the formation of acids.

Effects on the environment.

-Lowers soil pH, which affects mineral solubility.

                     Example: aluminum

-Lowers the pH of lakes and streams, which adversely affect aquatic life.