The Chemistry of Life:
Properties of Water
Ch. 2
Biology
Ms. Haut
Properties of Water
• Cohesive nature of
water
• Ability to moderate
temperature
• Unusual phase
changes
• Versatile solvent
http://www.thewaterfallpractice.co.uk/assets/images/waterfall_ir
eland_pdphoto.jpg
THE PROPERTIES OF WATER
1. Cohesion of Water
• Water is a polar
molecule, electrons
are shared unequally
• Cohesion is the ability
of water molecules to
attach to other water
molecules
– Attach by hydrogen
bonds
http://www.nsf.gov/news/special_reports/water/images/cp_photo.jpg
• In a water molecule, oxygen exerts a
stronger pull on the shared electrons than
hydrogen
– This makes the
oxygen end of the
molecule slightly
negatively charged
– The hydrogen end of
the molecule is slightly
positively charged
– Water is therefore a
polar molecule
(–)
(–)
O
H
(+)
H
(+)
Figure 2.9
• H+ atom is covalently
bonded to the oxygen via
a shared pair of
electrons.
• Oxygen is an
"electronegative" or
electron "loving" atom
compared with hydrogen
• "polar" molecule,
meaning that there is an
uneven distribution of
electron density
– This attraction forms weak
bonds called hydrogen
bonds
Surface Tension
• The cohesion of water molecules at the
surface of a body of water
• Due to hydrogen
bonding, water
molecules can move
from a plant’s roots
to its leaves
• Insects can walk on
water due to surface
tension created by
cohesive water
molecules
Water Spider
http://blogs.rep-am.com/nature/wp-content/uploads/2008/07/waterspider_qs3y2758_bf.jpg
Adhesion
http://farm1.static.flickr.com/200/480451566_e66f7cc4f3
.jpg?v=0
http://en.wikivisual.com/images/9/96/Water_drops_on_spider_we
b.jpg
• Water can also be attracted to other
materials.
Capillary Action
• When one water
molecule moves closer
to the straw molecules
the other water
molecules (which are
cohesively attracted to
that water molecule)
also move up into the
straw.
Water
Mercury
http://cwx.prenhall.com/petrucci/medialib/media_portfoli
o/text_images/FG13_04.JPG
http://www.mynewsletterbuilder.com/ex/template_content_corner/ex37/images/muirwoods-redwood-tree-1.jpg
Giant Redwoods
Plant Transpiration—aided by cohesion and adhesion
2. Water’s hydrogen bonds
moderate temperature
• Water has high specific
heat
• Specific heat = heat
needed to raise temp. of
1g of substance by 1ºC
• Boiling Point High ....
water stays liquid longer
• As such, water can act as
heat reservoire,
moderating Earth’s global
temperature
http://bio.winona.msus.edu/berg/IMAGES/earth_from
_space.jpg
2. Water’s hydrogen bonds
moderate temperature
• It takes a lot of energy to
disrupt hydrogen bonds
– able to absorb a great
deal of heat energy
without a large
increase in
temperature
– As water cools, a
slight drop in
temperature releases
a large amount of heat
http://clarkvision.com/galleries/images.yellowstone/web/c072091.01.03600.mamoth.hot.springs.jpg
– A water molecule takes a large amount of
energy with it when it evaporates
– This leads to evaporative cooling
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
3. Unusual Phase Change
• Like no other common
substance, water exists in
nature in all three
physical states:
– as a liquid
– as a gas
– as a solid
http://s3.amazonaws.com/readers/2008/11/11/iceberg2_1.jpg
Modified from PowerPoint lectures http://occawlonline.pearsoned.com
Gas
Liquid
Solid
Density of Water
• Ice is Less Dense than Liquid Water
• Molecules in ice are farther apart than those in
liquid water
• Water is densest at 4°C.
Hydrogen
bond
ICE
Hydrogen bonds are
stable
LIQUID WATER
Hydrogen bonds
constantly break and
re-form
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.
• Frozen water floats (left) and frozen benzene
sinks (right)
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
• Ice fishing
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
4. Water is a Versatile Solvent
• Also known as the “Universal solvent”.
• Polar substances are enveloped by hydration
spheres.
– “Like dissolves like!”
• Solutes whose charges or polarity allow
them to stick to water molecules dissolve in
water
– They form
aqueous
solutions
Na+
–
Na+
–
+
Cl–
+
–
+
–
+
–
Cl–
Ions in
solution
Salt
crystal
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
Properties of Water
Properties of Water
A molecule in which the charges are
unevenly distributed is called a
a)
b)
c)
d)
polar molecule.
cohesive molecule.
hydrogen molecule.
covalent molecule.
Properties of Water
2
Hydrogen bonds between water molecules
result from
a) adhesion between water molecules.
b) magnetic attractions between water
molecules.
c) uneven electron distribution in each water
molecule.
d) ionic bonds in the water molecule.
Acknowledgements
• Unless otherwise noted, illustrations are credited to
Prentice Hall and have been borrowed from Biology by
Miller and Levine, © 2007. These images have been
produced from the originals by permission of the
publisher. These illustrations may not be reproduced in
any format for any purpose without express written
permission from the publisher.
Acids, Bases, and pH
Ch. 2
Ms. Haut
Solutions and Suspensions
• Solutions and Suspensions
• A mixture is a material composed of two or more
elements or compounds that are physically mixed
but not chemically combined.
Strawberries and Sugar
http://myimages.bravenet.com/132/310/362/
6/06-09-09_blog-a.jpg
Solutions and Suspensions
• Two types of mixtures can be made with
water
– Solutions
– Suspensions
Solutions and Suspensions
• Two types of mixtures can be made with
water
– Solutions
• All the components of a solution are evenly
distributed throughout the solution.
• In a salt–water solution, table salt is the solute—
the substance that is dissolved.
• Water is the solvent—the substance in which the
solute dissolves
Solutions and Suspensions
• When a crystal of table
salt is placed in warm
water, sodium and
chloride ions are attracted
to the polar water
molecules.
• Ions break away from the
crystal and are
surrounded by water
molecules.
• The ions gradually
become dispersed in the
water, forming a solution.
Solutions and Suspensions
– Suspensions
• Some materials do not dissolve when placed in
water but separate into pieces so small that they
do not settle out.
• The movement of water molecules keeps the small
particles suspended.
Suspension of
flour in water
http://www.answers.com/topic/mixture
Some Important Biological Fluids Are
Both Solutions and Suspensions
• Blood is mostly water,
which contains many
dissolved
compounds.
• Blood also contains
cells and other
undissolved particles
that remain in
suspension as the
blood moves through
the body.
https://frontpage.northseattle.edu/judylearn/ANP%20128/ANP_128_Blood_C
omp.JPG
Acids, Bases, and pH
• Acids, Bases, and pH
• A water molecule can react to form hydrogen and
hydroxide ions.
H20  H+ + OH• Water is neutral because the number of positive
hydrogen ions (H+) produced is equal to the
number of negative hydroxide ions (OH-)
produced.
Acids, Bases, and pH
• The pH scale
– Measurement system to indicate the
concentration of H+ ions in solution.
– The pH scale ranges from 0 to 14.
Solution
Acid
Neutral
Base
pH range
H+/OH- ratio
0-6.999
concentration of H+ ions greater
than OH- ions
7.0
concentration of H+ ions and OHions is equal.
7.001-14
concentration of H+ ions less than
OH- ions
Acids, Bases, and pH
• Acids
– Any compound that forms
H+ ions in solution.
• Contain higher
concentrations of H+ ions
than pure water
– Strong acids tend to have
pH values that range from
1 to 3.
– The hydrochloric acid
produced by the stomach
to help digest food is a
strong acid.
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
Acids, Bases, and pH
•Bases
– A base is a compound that
removes H+ ions from a
solution.
• Basic, or alkaline,
solutions contain lower
concentrations of H+ ions
than pure water
– Strong bases, such as lye,
tend to have pH values
ranging from 11 to 14.
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
OH–
Acidic solution
• Each pH unit
represents a
tenfold
change in
concentration
of H+
Increasingly ACIDIC
(Higher concentration of
H+)
H+
NEUTRAL
[H+] = [OH–]
Neutral solution
Increasingly BASIC
(Lower concentration of
H+)
• The pH
scale
pH scale
Basic solution
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
Lemon juice;
gastric juice
Grapefruit juice
Tomato juice
Urine
PURE WATER
Human blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Oven cleaner
pH Indicators
• Cabbage Juice
– Boiled cabbage
creates a
bluish/purplish juice
that can be used to
test pH of
substances
http://www.chemistryland.com
pH Indicators
• Cabbage juice responds like
litmus paper
– Indicator turns:
• Red in Acids
• Blue in Bases
http://www.uniregensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusc
h/Grafik/cabbage.gif
http://www.howe.k12.ok.us/~jimaskew/litmus.jpg
pH Indicators
• pH paper
http://www.bio-world.com/images/061036.jpg
• phenolphthalein
-turns pink in
presence of base
http://ull.chemistry.uakron.edu/organic_l
Acids, Bases, and pH
• Buffers
– The pH of the fluids within most cells in the human
body must generally be kept between 6.5 and 7.5.
– If the pH is lower or higher, it will affect the chemical
reactions that take place within the cells.
• enzymes denature & reactions stop (That’s a bad
thing!)
http://diverge.hunter.cuny.edu/~weigang/Images/05-06_denaturation_1.jpg
Acids, Bases, and pH
• Controlling pH is important for maintaining homeostasis.
• Buffers are weak acids or bases that can react with
strong acids or bases to prevent sharp, sudden changes
in pH.
– They accept H+ ions when they are in excess and
donate H+ ions when they are depleted
http://www.colorado.edu/intphys/Class/IPHY3430-200/image/buffer.jpg
Connection: Acid precipitation
threatens the environment
• Some ecosystems are threatened by acid
precipitation
• Acid precipitation is formed when air pollutants
from burning fossil fuels combine with water vapor
in the air to form sulfuric and nitric acids
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
– These acids can kill fish, damage buildings, and
injure trees
– Regulations, new technology, and energy
conservation may help us reduce acid
precipitation
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2003.
Acids, Bases, and pH
Acids, Bases, and pH
1
A dissolved substance is called a
a)
b)
c)
d)
solvent.
solution.
solute.
suspension.
Acids, Bases, and pH
2
A compound that removes ions from a
solution is called a(an)
a)
b)
c)
d)
base.
buffer.
acid.
salt.
Acids, Bases, and pH
3
On a pH scale, a value of 2 means that the solution
has
a) equal concentrations of H+ and OH- ions.
b) the same concentration of H+ ions as pure water.
c) higher concentration of H+ than in pure water.
d) lower concentration of H+ than in pure water.
Acids, Bases, and pH
4
Tomato juice has a pH of 4, while soap has a pH of
10. How much more acidic is the juice?
a)
b)
c)
d)
6 times more acidic
1,000,000 times more acidic
60 times more acidic
1,000 times more acidic
Acknowledgements
• Unless otherwise noted, illustrations are credited to
Prentice Hall and have been borrowed from Biology by
Miller and Levine, © 2007. These images have been
produced from the originals by permission of the
publisher. These illustrations may not be reproduced in
any format for any purpose without express written
permission from the publisher.