BIOL 111 Chapter 3

Thursday, September 2, 2010 | next »

Water

Essential for life on a chemical level:

• Cells are 75-80% water
• Water supports large bio-diverse environments
• Most biological reactions take place in water
• Water regulates temperature
• Ice is less dense than water, so it insulates deeper liquid water

Chemical Properties

Polar molecule due to electronegativity of oxygen

• Hydrogen bonds are more stable in ice crystals
• Cohesion (surface tension)
• Adhesion
• High specific heat capacity
  It takes a lot of energy to raise the temperature of water
• Hydrophilic interactions

Life is Aqueous

Important Terms

Solute

stuff dissolved in the solvent

Molarity (M)

moles of solute per liter

Mole

6.02×10²³ objects (Daltons/gram)

Molar Mass = grams/mole (how much matter is in a mole of a substance)

pH and Buffers

Water can break into ions:

2H₂O ↔ H⁺ + OH^-

2H₂O ↔ H₃O⁺ + OH^-

Acid

Increases H⁺ in solution

Base

Decreases H⁺ in solution

pH is a "count" of how many H⁺ in solution:

Why 1-14?

Behavior of acids and bases in aqueous solution is constant at 25°C and is expressed as:

[H⁺] × [OH^-] = 10^-14

pH = -log(H⁺), therefore Water = -log(10^-7) = 7 (neutral)

Buffering

Most living cells exist between pH 6.5-8.0

Buffering molecules in or around cells minimize changes in H⁺ and OH^– by adding/removing H⁺ ions as needed

EX: Carbonic acid can give up a hydrogen atom in your blood while carrying oxygen at the same time
(H₂CO₃ ↔ HCO₃^– + H⁺)