Transcript Lesson Overview

Lesson Overview
Properties of Water
Lesson Overview
2.2 Properties of Water
Lesson Overview
Properties of Water
THINK ABOUT IT
“the blue planet,”
The very presence of liquid water
tells a scientist that life may also
be present on such a planet.
Lesson Overview
Properties of Water
The Water Molecule
Water has very unique properties!
Water is one of the few compounds found in a liquid state over most of Earth’s
surface.
Like other molecules, water (H2O) is neutral
Because water is a polar molecule, it is able to form multiple hydrogen bonds,
which account for many of water’s special properties.
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Properties of Water
Polarity
Polar Molecule-The
oxygen atom is on one
end of the molecule and
the hydrogen atoms are
on the other.
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Properties of Water
Polar- molecule with uneven charges
oxygen- slight negative
charge
hydrogen -slight positive
charge.
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Properties of Water
Hydrogen Bonding
Polar molecules such as water
can attract each other.
Hydrogen bond -attraction
between a hydrogen atom on
one water molecule and the
oxygen atom on another
Hydrogen bonds are not as
strong as covalent or ionic
bonds
Lesson Overview
Properties of Water
Cohesion
Cohesion -attraction
between molecules of the
same substance.
A single water molecule may be
involved in as many as four
hydrogen bonds at the same time,
water is extremely cohesive.
Lesson Overview
Properties of Water
Cohesion
Cohesion causes water molecules to be drawn together,
which is why drops of water form beads on a smooth
surface.
Cohesion also produces surface tension, explaining why
some insects and spiders can walk on a pond’s surface.
lizard
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Properties of Water
Adhesion
Adhesion is an attraction between molecules of different
substances.
meniscus- caused because the adhesion between water
molecules and glass molecules is stronger than the
cohesion between water molecules.
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Properties of Water
Adhesion
Adhesion-Capillary action is one of the
forces that draws water out of the roots of a
plant and up into its stems and leaves.
Cohesion holds the column of water
together as it rises.
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Properties of Water
Heat Capacity
Because of the multiple hydrogen bonds between water molecules, it
takes a large amount of heat energy to cause those molecules to move
faster and raise the temperature of the water.
Water’s heat capacity- the amount of heat energy required to increase
its temperature, is relatively high.
Large bodies of water, such as oceans and lakes, can absorb large
amounts of heat with only small changes in temperature. This protects
organisms living within from drastic changes in temperature.
At the cellular level, water absorbs the heat produced by cell processes,
regulating the temperature of the cell.
water capacity
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Properties of Water
Solutions and Suspensions
Water’s polarity gives it the ability to dissolve both ionic compounds and
other polar molecules. When a given amount of water has dissolved all of
the solute it can, the solution is said to be saturated.
If a crystal of table salt is placed in water, sodium and chloride ions on the
surface of the crystal are attracted to the polar water molecules.
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Properties of Water
Solutions
Ions break away from the crystal and are surrounded by water
molecules.
The ions gradually become dispersed in the water, forming a type of
mixture called a solution.
Lesson Overview
Properties of Water
Solutions
All the components of a solution are evenly distributed throughout the
solution.
In a saltwater solution, table salt is the solute—the substance that is
dissolved.
Water is the solvent—the substance in which the solute dissolves.
When a given amount of water has dissolved all of the solute it can, the
solution is said to be saturated.
Lesson Overview
Properties of Water
Solutions and Suspensions
Water is not always pure; it is often found as part of a mixture.
A mixture is a material composed of two or more elements or compounds
that are physically mixed together but not chemically combined.
Living things are in part composed of mixtures involving water.
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Properties of Water
Suspensions
Suspensions- mixtures of water and nondissolved particles that do not
settle out.
Some of the most important biological fluids are both solutions and
suspensions.
Blood is mostly water. It contains many dissolved compounds, but also
cells and other undissolved particles that remain in suspension as the
blood moves through the body.
blood
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Properties of Water
Acids, Bases, and pH
Acids taste sour, are corrosive to metals, change litmus (a dye extracted from
lichens) red, and become less acidic when mixed with bases
Dissolve in water to release hydrogen ions into solution:
HCl
H2O
+
H
-
+
Cl
Bases feel slippery, change litmus blue, and become less basic when mixed
with acids.
Dissolve in water to release hydroxide ions (OH-) into solution
NaOH
H2O
OH-
+
Na+
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Properties of Water
pH
Acids
the concentration of hydrogen ions H+
Bases
the concentration of hydrogen ions H+
more OH- ions(accepts H+)
The acidity or basicity of something, therefore, can be
measured by its hydrogen ion concentration.
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Properties of Water
pH scale
+
pH = -log [H ]
For example, a solution with [H+] = 1 x 10-7 moles/liter
has a pH equal to 7
pH scale ranges from 0 to 14.
Acids- pH between 0 and less than 7 (lower
pH means higher [H+]).
Bases- pH greater than 7 and up to 14 are bases (higher
pH means lower [H+]).
Neutral pH = 7, for example, pure water.
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pH
Properties of Water
Lesson Overview
Properties of Water
Neutralization
A neutralization reaction of an acid with
a base will always produce water and a salt
Acid
Base
Water
Salt
HCl
+
NaOH
→
H2O
+
NaCl
HBr
+
KOH
→
H2O
+
KBr
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Properties of Water
Acids, Bases, and pH
Acid–base homeostasis is the part of human
homeostasis concerning the proper balance
between acids and bases, called body pH. The body is very
sensitive to its pH level, so strong mechanisms exist to
maintain it.
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Properties of Water
Buffers
The pH of the fluids within most cells in the
human body is kept between 6.5 and 7.5 in order
to maintain homeostasis.
Buffer-controls pH
usually a weak acids or bases that can react
with strong acids or bases to prevent sharp,
sudden changes in pH
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Properties of Water
Buffers
Adding acid to an unbuffered solution causes the pH
of the unbuffered solution to drop. If the solution
contains a buffer, however, adding the acid will cause
only a slight change in pH.
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Properties of Water
Exercise
Exercise has many short-term (acute) and long-term
effects on the body:
Increased activity leads to increased carbon dioxide
and hydrogen levels in the blood.
( metabolism)
They lower blood pH, increasing acidity, beyond
optimal levels.
The brain stimulates the heart rate to increase:
remove excess carbon dioxide
lungs & kidneys.
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Properties of Water
BLOOD pH
If the pH of the body gets too low (below 7.4), acidosis results. This can be serious,
because many of the chemical reactions that occur in the body, especially those
involving proteins, are pH-dependent. (enzymes)
Ideal pH of the blood = 7.4.
If the pH drops below 6.8 or rises above 7.8, death may occur.
Lesson Overview
Properties of Water
Buffering Systems
There are three primary systems that regulate the H+
concentration in the body fluids to prevent acidosis or
alkalosis:
(1) the chemical acid-base buffer systems of the body fluids,
which immediately combine with acid or base to prevent
excessive changes in H+ concentration;
(2) the respiratory center, which regulates the removal of CO2
(and, therefore, H2CO3) from the extracellular fluid; and
(3) the kidneys, which can excrete either acid or alkaline urine,
thereby readjusting the extracellular fluid H+ concentration
toward normal during acidosis or alkalosis.
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Properties of Water
Hydrogen (H + ) ions, and carbonic acid (H 2 CO 3 ) are both classified as body acids, substances
that either donate hydrogen ions (such as H 2 CO 3
Lesson Overview
Properties of Water
In the lungs, the reaction is reversed and produces carbon dioxide gas, which
you exhale.
As it enters the blood, carbon dioxide (CO2) reacts with water to produce carbonic
acid (H2CO3), which is highly soluble.
This chemical reaction enables the blood to carry carbon dioxide to the lungs.
video
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Properties of Water
Homeostasis
Acidosis is an “abnormal condition of” (-osis) too much body “acid.” Because a person
exhales just enough CO 2 , there isn’t time for too much CO 2 to accumulate within
the erythrocytes and build up too much carbonic acid, H 2 CO 3 , or H + ions.
When a person hyperventilates too much CO 2 is exhaled from the body. Thus, not
enough CO 2 is left to react with H 2 O inside the erythrocytes. There is not enough
carbonic acid (H 2 CO 3 ) or hydrogen ion (H + ) produced. The resulting state is
alkalosis .
Lesson Overview
Properties of Water
Acid Base Balance