water water: an absolute necessity for life ¾ of the planet is covered by it life existed in...
TRANSCRIPT
WaterWater: An absolute necessity for life
¾ of the planet is covered by itLife existed in water 2 Billion years prior to adapting to
land60% of human weight from water83% of human blood composition
Where water exists, life may be foundWater is critical to cell biochemistryWater is critical for photosynthesis
Water is the ‘universal solvent’
Water’s structure
Simple molecular structure with Oxygen bound to 2 Hydrogen atoms by single covalent bonds
Electronegativity of O is much greater than H – so the bonds between these atoms are “polar”
Hydrogen bonding:outstanding chemical property of
water
“The polarity of water impacts water’s chemistry and the chemistry of life…”
Properties of water
• Cohesion =
• Adhesion =
• High specific heat =
• High heat of vaporization =
• Solid water less dense than liquid =
• Has solvent properties =
Water can form ions• The covalent bonds of water can break
spontaneously to produce H+ and OH-
H2O OH- (hydroxide ion) + H+ (hydrogen ion)
• At 25° C, one liter of water contains one ten-millionth (10-7) molemole of H+ ions
• A MoleMole is equal to the weight of a substance (in grams) that corresponds to the atomic mass of the atoms forming the substance
• H+ has an atomic mass of 1, so a mole of H+ would weigh 1 gram
Water and pH
pH = -log [H+]
• Therefore, pure water, having 10-7 moles/liter concentration of H+, has a pH of 7.0
• A pH of 7.0 is determined to be “neutral” due to equal concentrations of H+ and OH- ions
pH and logarithms
• Note that the pH scale is logarithmic, meaning that a difference of 1 of pH means a 10-fold change in H+ ion concentration
• Therefore, a solution having a pH of 3 has 10X more H+ ions than a solution with a pH of 4; 100X more H+ than a solution with a pH of 5
Acids and bases
AcidsAcids• Any solution with a pH
less than 7.0• The stronger an acid is,
the more H+ ions it releases to solution
• High amounts of H+ ions are causticcaustic = capable of burning, corroding, or destroying living tissue
BasesBases• Any solution with a pH
greater than 7.0• The stronger a base is,
the more OH- or similar ions it releases to solution
• High amounts of OH- ions are causticcaustic
Buffers help stabilize pH
• A buffer is a substance that resists changes in pH• Within organisms, buffers consist of acid-base pairings
• In human blood, carbonic acid (H2CO3) serves as a buffer which can split to form bicarbonate ion (HCO3
-) and a Hydrogen ion (H+) to aid in stabilizing the pH
Articles on Reserve for Article Review #2
• Taylor, D. 2007. Employment preferences and salary expectations of students in science and engineering. Bioscience. 57: 175-185.
• Ostfeld, R.S. et al. 2006. Controlling ticks and tick-borne zoonoses with biological and chemical agents. Bioscience. 56: 383-394.
• DeLong, E.F. 2003. A plentitude of ocean life. Natural History. 112: 40-46.
• Schmid-Hempel, P. 2003. Fight of the bumblebee. Natural History. 112: 52-59.
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