Chap 3.docx

**CHAPTER 3** ============= WATER AND THE FITNESS OF THE ENVIRONMENT ======================================== **Water: Hydrogen Bonding, Solubility, and Specific Heat** Cells are 70-95% water. Water covers 70% of the earth's surface. \>\>\>\>\>Some of the most biologically important polar coval...

**CHAPTER 3** ============= WATER AND THE FITNESS OF THE ENVIRONMENT ======================================== **Water: Hydrogen Bonding, Solubility, and Specific Heat** Cells are 70-95% water. Water covers 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**. 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 (see fig. 3.8 and fig 3.9)**. \-\--**Solution** \-\--**Solvent** \-\--**Solute** \-\--**aqueous solution** Water\'s polarity along with the hydrogen bonding can organize water molecules into a higher level of structural order (see fig. 3.2). 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** ------------------- ---------------------------------- ---------------------------------- ------------------------------- Temperature scale Temperature at which water melts Temperature at which water boils Temperature of the human body Celsius 0 ^o^C 100 ^o^C 37 ^o^C Fahrenheit 32 ^o^F 212 ^o^F 98.6 ^o^F Kelvin 273 ^o^K 373 ^o^K 310 ^o^K ------------------- ---------------------------------- ---------------------------------- ------------------------------- \-\--**Specific heat** \-\--**calorie (cal)** \-\--**Kilocalorie (kcal) or Calorie (dietary calorie)** 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** Water molecules have "sticky" emergent properties including: **cohesion, adhesion,** and **surface tension (see fig 3.3).** \-\--**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** 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** 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 (H~3~O^+^)**. \-\--**Hydroxide ion (OH^-^)**. **ACIDS AND BASES** At equilibrium in pure water at 25 ^o^C -the number of H^+^ atoms = the number of OH^-^ atoms -the molar concentration of H^+^ = \[H^+^\] = 10^-7^ M \-\--**Acid** \-\--**Base** For an acidic solution \[H^+^\]\>\[OH^-^\] For a basic solution \[H^+^\]\\>\>\>\>\>**pH Scale (see fig 3.11)** 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 an acidic solution \[H+\]=10^-5^ and pH =5 For a basic solution \[H+\]=10^-9^ and pH = 9 \>\>\>\>\>\>**Buffers** **Hemoglobin as a Buffer** \-\--**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 Drop in pH Rise in pH HCl + NaHCO~3~ ⇋ H~2~CO~3~ + NaCl NaOH + H~2~CO~3~ ⇋ NaHCO~3~ + H~2~O