Chapter 3 Water and the Fitness of the Environment

Figure 3.x1 Water

Living things 75 – 90% water ¾ of Earth covered with water Water found on Earth as solid, liquid, gas Exceptional substance

Figure 3.0 Earth

Figure 3.5x1 Ice, water, and steam

Properties of water: 1)Cohesiveness – H 2 O molecules stick together as a result of H bonds as seen in water transport in plants (vs. gravity) surface tension – measure of how difficult it is to break the surface of a liquid -causes water on a surface to bead into a spherical shape to produce low ratio of area to volume maximizing # of H bonds able to form (water has a greater surface tension than most liquids)

Figure 3.1 Hydrogen bonds between water molecules

Figure 3.3 Walking on water

adhesion – clinging of substance to a different substance (IMF) hydrophilic – materials that have affinity for water -ex: glass imbibition – uptake of water by a hydrophilic porous material

Figure 3.2 Water transport in plants

2) High specific heat – water stabilizes air temperature by absorbing heat from warmer air & releasing stored heat to air that is cooler -water has high specific heat – slight change in its temperature accompanied by absorption or release of relatively large amount of heat

3)High heat capacity – bodies of water hold heat/release heat heat of vaporization – amt. of heat it must absorb for 1g to change from liquid to gas evaporative cooling – as liquid evaporates, surface of the liquid remaining cools down

Figure 3.4 Evaporative cooling

4)Powerful solvent – causes breakdown (dissolution) of many compounds solvent, solute, solution -polarity of the molecule attracts to charged & polar substances causing dissolution of solutes 5)Less dense as a solid – expansion as it solidifies (ice floats)

Figure 3.7 A crystal of table salt dissolving in water

Figure 3.6x2 Ice floats and frozen benzene sinks

Figure 3.5 The structure of ice (Layer 2)

Water dissociates -into H + and OH - -reversible & statistically rare, but important to life Acids – release H + in solution HCl H + + Cl - Bases – release OH - in solution NaOH Na + + OH -

Unnumbered Figure (page 47) Chemical reaction: hydrogen bond shift

pH scale – measures H + concentration in a solution -pH = -log [ H + ] Buffers – allow biological fluids to resist their own pH changes when acids/bases are introduced -most are weak acids or weak bases -ex: H 2 CO 3 HCO H + (H + donor) (H + acceptor)

Figure 3.9 The pH of some aqueous solutions