D’YOUVILLE COLLEGE
BIOLOGY 102 - INTRODUCTORY BIOLOGY II
LECTURE # 2 SIMPLE CHEMISTRY II
4.
Water:
• polar compound: ability of a water molecule to hydrogen bond with other water
molecules (figs. 2 – 13, 3 - 2 & ppts. 1 & 2) gives water exceptional properties: cohesion,
adhesion, surface tension; these properties benefit living things in various ways
- cohesion and adhesion promote capillary action of water (fig. 3 – 3 & ppt. 3)
- surface tension is responsible for ‘skin-like’ quality of water-air interface (fig.
3 – 4 & ppt. 4)
• specific heat: water consumes large amount of heat per degree rise in
temperature (1 cal/gm. = 10x specific heat of iron); this is because heat is consumed in
breaking hydrogen bonds before increasing kinetic energy of molecules; this property
moderates temperatures (fig. 3 – 5), making earth environment compatible with life
- heat of vaporization – hydrogen bonding also increases the amount of heat
necessary to evaporate a gram of water; this makes it effective at cooling surfaces where
evaporation occurs, e.g. sweating
- ice (fig. 3 – 6 & ppt. 5) – less dense than liquid water due to stabilization of
hydrogen bonding; this decrease in density occurs at 4o C.; thus bodies of water freeze
at surface
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• solvent of living systems: polar nature permits water to hydrogen bond to
other polar substances (e.g. sugars), or to ionic substances (e.g. sodium chloride) (fig. 3 –
7 & ppt. 6); water dissolves ionic & other polar compounds (fig. 3 – 8 & ppt. 7)
(hydrophilic); excludes non-polar compounds, e.g. oils (hydrophobic)
• medium for reactions of living systems; participant in reactions of living
systems: dehydration syntheses, hydrolyses
5.
Acids & Bases:
• ionization of water: 10 -7 moles per liter are dissociated into H+ & OH-; the
product of the concentrations of these two ions is 10-14 (ppt. 8)
- acids produce hydrogen ions in solution (H+ donors)
- bases remove hydrogen ions from solution (H+ accepters)
• concentration of acid: moles per liter
• strength of acid: degree of ionization
• pH scale (fig. 3 – 10 & ppt. 9): convenient way to express hydrogen ion
concentrations in simple whole numbers; 7 is neutral; 0 is extremely acidic; 14 is
extremely basic
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