The Chemistry of Life: Properties of Water Ch. 2 Biology Ms. Haut

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


• Frozen water floats (left) and frozen benzene sinks (right)


• Ice fishing


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+

+

+

+

+


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


• Two types of mixtures can be made with water– Solutions– 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


• 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.


– 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• 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.


• 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– 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.



•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.


• The pH scale

• Each pH unit represents a tenfold change in concentration of H+

pH scale

Acidic solution

Neutral solution

Basic solution

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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–


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


• 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


• 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


– These acids can kill fish, damage buildings, and injure trees

– Regulations, new technology, and energy conservation may help us reduce acid precipitation




A dissolved substance is called a a) solvent.

b) solution.

c) solute.

d) suspension.

11


A compound that removes ions from a solution is called a(an)

a) base.

b) buffer.

c) acid.

d) salt.

22


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


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.

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The Chemistry of Life: Properties of Water Ch. 2 Biology Ms. Haut