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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_ireland_pdphoto.jpg
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
THE PROPERTIES OF WATER
http://www.nsf.gov/news/special_reports/water/images/cp_photo.jpg
– 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
• In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen
Figure 2.9
(–)
O
(–)
(+)(+)
H H
• 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/water-spider_qs3y2758_bf.jpg
Adhesion
• Water can also be attracted to other materials.
http://en.wikivisual.com/images/9/96/Water_drops_on_spider_web.jpg
http://farm1.static.flickr.com/200/480451566_e66f7cc4f3.jpg?v=0
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.
http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/FG13_04.JPG
Water Mercury
Giant Redwoods
Plant Transpiration—aided by cohesion and adhesion
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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/c072091.01.03-
600.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
Modified from PowerPoint lectures http://occawlonline.pearsoned.com
http://s3.amazonaws.com/readers/2008/11/11/iceberg2_1.jpg
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
ICEHydrogen bonds are
stable
LIQUID WATERHydrogen 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
Ions in solution
Salt crystal
Cl–
Na+
Cl–
–
– –
–
–Na+
+
+
+
+
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) polar molecule.
b) cohesive molecule.
c) hydrogen molecule.
d) covalent molecule.
Properties of Water
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.
22
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.
http://myimages.bravenet.com/132/310/362/6/06-09-09_blog-a.jpg
Strawberries and Sugar
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_Comp.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 pH range H+/OH- ratio
Acid 0-6.999concentration of H+ ions greater than OH- ions
Neutral 7.0concentration of H+ ions and OH- ions is equal.
Base 7.001-14concentration 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.
• The pH scale
• Each pH unit represents a tenfold change in concentration of H+
pH scale
Acidic solution
Neutral solution
Basic solution
Incr
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CID
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igh
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on
cen
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ion
of
H+)
Incr
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ng
ly B
AS
IC(L
ow
er
con
cen
trat
ion
of
H+)
NEUTRAL[H+] = [OH–]
Lemon juice; gastric juice
Grapefruit juice
Tomato juice
Urine
PURE WATER
Seawater
Milk of magnesia
Household ammonia
Household bleach
Oven cleaner
Human blood
H+
OH–
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.
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.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/Grafik/cabbage.gif
http://www.howe.k12.ok.us/~jimaskew/litmus.jpg
pH Indicators
• pH paper
• phenolphthalein
-turns pink in presence of
base
http://www.bio-world.com/images/061036.jpg
http://ull.chemistry.uakron.edu/organic_lab/distribution/dist13.gif
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
• 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
Connection: Acid precipitation threatens the environment
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
A dissolved substance is called a a) solvent.
b) solution.
c) solute.
d) suspension.
11
Acids, Bases, and pH
A compound that removes ions from a solution is called a(an)
a) base.
b) buffer.
c) acid.
d) salt.
22
Acids, Bases, and pH
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.
33
Acids, Bases, and pH
Tomato juice has a pH of 4, while soap has a pH of 10. How much more acidic is the juice? a) 6 times more acidic
b) 1,000,000 times more acidic
c) 60 times more acidic
d) 1,000 times more acidic
44
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.