properties of water water statistics covers 75% of earth’s surface covers 75% of earth’s surface...
TRANSCRIPT
Properties of Water
Water statistics
Covers 75% of Earth’s surface 97% oceans 3% freshwater
2% (of Total) in ice caps and glaciers 1% in lakes, underground, or in atmosphere
(usable by humans)
Makes up 70% of the human body 92% of blood plasma 80% of muscle tissues 60% of red blood cells
(why understanding it is important!)
Physical properties Water: Is clear, colorless, odorless, and tasteless
* Colors, tastes and odors are caused by substances dissolved in the water.
Boils at 100°C Freezes at 0°C Density = 1.0 g/mL (at 4°C)
CohesionAdhesionHigh Specific HeatHigh Heat of VaporizationLess Dense as a Solid
Properties of Water
Water Polar molecule
molecule with uneven distribution of charge
water is polar, O atom pulls electrons from H atoms causing an unequal sharing of electrons
Biochemistry
The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond.
Each water molecule can form hydrogen bonds with up to four neighbors.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 3.1
HYDROGEN BONDS The hydrogen
bonds joining water molecules are weak, about 1/20th as strong as covalent bonds.
They form, break, and reform with great frequency
Extraordinary Properties that are a result of hydrogen bonds.
Cohesive behavior Resists changes in
temperature High heat of vaporization Expands when it freezes Versatile solvent
Properties of Water
Cohesion is the tendency of molecules of the same kind to stick to one another.
Water has stronger cohesion than most liquids
Cohesion pulls molecules at the surface tightly together, forming a film-like boundary, creating water’s surface tension.
Surface Tension The collective strength of hydrogen bonds
forms a film on the surface of water Ex: floating a paper clip, “water striders”, water
beading on waxed car
http://wine1.sb.fsu.edu/chm1045/notes/Forces/Liquids/Forces03.htm
AirWater
Adhesion-Attraction between unlike molecules Ex: water moving
up the roots of a tree this is called capillary action
Adhesion Water molecules attracted to sides
of container
Biochemistry
Capillary Action Capillary action = Water is able to
“climb” objects against the forces of gravity
Think of the (+) and (-) ends of a water molecule acting like suction cups, and a water molecule is using them to climb up a glass building
http://kingfish.coastal.edu/biology/sgilman/770lecwatersalt.htm
Water is Less Dense as a Solid Density of ice (at 0°C) is 0.917
g/mL, so ice floats in water. Most liquids become
more dense as you cool them. However, when water freezes, a large expansion occurs.
Water “organizing” with
H bonds as it freezes.
Forms hexagon shapes.
* Where have you see H2O in repeating
hexagonal patterns before?
So ice is able to float (just barely)
Universal Solvent Solvent – a substance that
dissolves another substance What dissolves in water? Salt, Sugar, Carbon Dioxide,
Oxygen, MANY more! For an object to dissolve in water it
must also be a polar molecule! This is why oil and water do not mix, oil
is NON-polar
High Specific Heat
•Water resists temperature change, both for heating and cooling.
•Water can absorb or release large amounts of heat energy with little change in actual temperature.
At the beach, why is the sand hotter than water at noon but cooler than water at midnight?
Water has a High Heat of Vaporization Evaporative Cooling -
the cooling of a surface occurs when the liquid evaporates
This is responsible for: Moderating earth’s
climate Preventing
organisms from overheating
Discussion Questions Which property of water causes the
cracks in the pavement in cold climates?
Why does a meniscus form on the surface of the water in a graduated cylinder?
What property of water best describes the ability of water to clean our clothes?
Acids, Bases, and pH
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pH scale
– Measurement system that indicates the concentration of hydrogen (H+) ions in solution A scale of 1-14 is used to describe
pH
AcidsAcids
have a pH range of 1-6
Produce lots of H+ ions
Bases
Bases have a pH range of 8 to 14
Contain lots of OH-ions and fewer H+ ions
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Acids and Bases Acid – any substance that forms hydrogen
ions (H+) in water Acidic solutions contain higher
concentrations of H+ ions and pH lower than 7.
Base – any substance that forms hydroxide ions (OH-) in water Basic, or alkaline, solutions contain lower
concentrations of H+ ions and pH higher than 7.
Buffers A substance that prevents sharp,
sudden changes in pH (neutralization).
Produced naturally by the body to maintain homeostasis
Weak Acid Weak Base