4.4. Life and Water
Wednesday, September 09, 2009
7:17 AM
• All life depends on water
○ Cells range from 70% to 95% water
○ In multicelled organisms, cells surrounded by fluid that
is mostly water (interstitial fluid)
A. Water Structure
 bent molecule
 O atom "hogs" the electrons it shares with the H
atoms
 creates a polar molecule (though not charged)
 as a result, water molecules are attracted to each
other
Chapter 4 -- Inorganic Chemistry Page 1
other
 these attractions make water "sticky"
 cohesion = water molecules sticking to each other
□ Ex: water beads up on the hood of a car
 adhesion = water molecules sticking to other
molecules or surfaces
□ Ex: meniscus in a glass tube
B. Acids, bases, and pH
 acids = any substance that releases hydrogen ions (H+) in
water
Ex:
HCl → H+ + Cl(hydrochloric acid)
 bases = any substance that releases ions which can
Chapter 4 -- Inorganic Chemistry Page 2
 bases = any substance that releases ions which can
combine with H+ (usually OH- ions)
NaOH → Na+ + OH-
Ex:
(sodium hydroxide)
OH- + H+ →
Notice:
 pH scale
 salts = compounds which form when acids react with bases
Ex: HCl + NaOH → H2O + NaCl
(sodium chloride)
□ in water, most salts dissociate into ions
Ex: K+, Na+, Ca++, Cl-
 buffers
□ substances which help to control pH levels by either
combining with H+ or releasing H+
□ important throughout various fluids in living organisms
Ex: H2CO3 ↔ HCO3- + H+
(carbonic acid)
(bicarbonate ion)
Chapter 4 -- Inorganic Chemistry Page 3
Chapter 4 -- Inorganic Chemistry Page 4