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Chapter 3

BIL 150 Chapter Notes - Chapter 3: Self-Ionization Of Water


Department
Biology
Course Code
BIL 150
Professor
Gaines Michael
Chapter
3

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Chapter 3 – Water and Life
Water is the biological medium on earth, the molecule that supports all of
life
Shape of Water
oWater is held together by 2 Hydrogen and 1 Oxygen atoms
oSince oxygen is more electronegative than hydrogen, the electrons
of the covalent bonds spend more time closer to oxygen than to
hydrogen, making them polar covalent bonds
oDue to this unequal sharing of electrons, water is known as a polar
molecule
Four emergent properties of water contribute to Earth’s suitability for life
oCohesion of water molecule allow hydrogen bonds to hold a
substance together (water is attracted to water)
Cohesion due to hydrogen bonding contributes to the
transport of water and dissolved nutrients against gravity in
plants
Adhesion is the clinging of one substance to another (water
is attracted to other substances)
Surface tension is a measure of how difficult it is to stretch
or break the surface of a liquid (spiders walking on water)
Water has a high surface tension
oModeration of temperature by water

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Water moderates air temperature by absorbing heat from air
that is warmer and releasing the stored heat to air that is
cooler
Water has a high specific heat, and this causes water to
have the ability to stabilize temperature
Specific heat – the amount of heat that must be
absorbed or lost for 1g of that substance to change its
temperature by 1 C
Because of its high specific heat, water will change its
temperature less than other liquids when it absorbs or
loses a given amount of heat
Water has evaporative cooling powers
Heat of Vaporization – the quantity of heat a liquid
must absorb for 1g of it to be converted from the liquid
to the gaseous state
oFor the same reason water has a high specific
heat, it also has a high heat of vaporization
oThis is a result of the strength of the hydrogen
bonds that must be broken before the
molecules can exit from the liquid in the form of
water vapor
As liquid evaporates, the surface of the liquid that
remains behind cools down (temperature decreases)
(evaporative cooling)
oThis occurs because the “hottest” molecules
(greatest kinetic energy) are most likely to
leave as gas
oEvaporative cooling contributes to the stability
of temperature in lakes and ponds
oFloating of ice on liquid water
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