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Water is ESSENTIAL to life
.
Living organisms are composed mostly of water.
Humans – 65%Jellyfish – 90%Tomato – 90%Elephant – 70%
• H atoms are “attached” to one
side of the O atom• This results in water molecule having a
(+) charge on the side
where the H atoms are and
a (–) charge on the side where oxygen
is.
• This uneven distribution of charge is called polarity.
• Opposite electrical charges attract
• Water molecules tend to attract each other– Side with H atoms (+)
attracts O side (-) of a different water molecule
The +/- attraction between the H (+) of one water molecule and the O (-) of the adjacent water molecule.
Oxygen is slightly negative
Hydrogen is slightly positive
COHESION
• Force that holds molecules of a single substance together is cohesion.
• Cohesion is due to hydrogen bonding between water molecules.
• Contributes to upward movement of water from roots to leaves in plants.
SURFACE TENSION
• Related to cohesion because water molecules are attracted to other water molecules.
• Water molecules at the surface are pulled into body of water which causes it to bead up.
• Because of surface tension, water holds its shape and will not spread out
• For water to spread out, surface tension must be reduced – Chemicals such as
surfactants can reduce the surface tension
• Surface tension enables water-striders to run on water without breaking the surface
ADHESION• Attractive force
between two particles of different substances– Water molecules and
glass molecules
• Capillarity is the attraction between molecules that results in rise of liquid when it is in contact with solid
Temperature Moderation
• Water can absorb or release large amounts of energy in the form of heat with only a slight change in temperature.– known as Heat Capacity
• Another result of the multiple H bonds
• A large amount of heat energy is needed for movement of water molecules to increases the temperature
• Hot summer day – water can absorb large amount of energy from sun and can cool the air without large increase in water temp.
• At night –
gradual cooling water warms the air
• As liquid evaporates, surface of liquid left behind cools down
• Evaporative cooling prevents organisms from overheating – Evaporation of sweat
releases body heat and prevents overheating.
High Heat of High Heat of VaporizationVaporization
Water is Less Dense as Water is Less Dense as a Solida Solid
•Which is ice and which is Which is ice and which is
water?water?
Water is Less Dense as Water is Less Dense as a Solida Solid
• Ice is less dense Ice is less dense as a solid than as a liquid (ice floats)
• Liquid water has hydrogen bonds hydrogen bonds that are constantly being broken and constantly being broken and reformed.reformed.
• Frozen water Frozen water forms a crystal-like latticecrystal-like lattice whereby molecules are set at fixed distances.
Mixtures
• Composed of two or more elements or compounds that are physically mixed together but not chemically combined
• Water can make 2 types of mixtures: solutions & suspensions
• Suspension: mixtures of water and nondissolved material
• Biological example: blood
SolutionA mixture of…
• Solute– A substance that is put INTO the solvent
to dissolve.
• Solvent– Substance that does dissolves the solute– Water = Universal Solvent
Acids & Bases• An important aspect of a living system is the
degree of acidity or alkalinity• pH scale ranges from 0 – 14• Acids – range from 0 – 6 (0 strongest)
• Neutral is 7• Bases - range from 8 – 14 (14 strongest)