1. The Chemistry of Life: Properties of Water
Biology
Ms. Haut

2. Properties of Water Cohesive nature of water
Ability to moderate temperature
Unusual phase changes
Versatile solvent

3. 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

4. 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

5. 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

6. Surface Tension
The cohesion of water molecules at the surface of a body of water

7. 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

8. Adhesion Water can also be attracted to other materials.
Water can also be attracted to other materials.

9. 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

10. Plant Transpiration—aided by cohesion and adhesion
Giant Redwoods
Plant Transpiration—aided by cohesion and adhesion

11. 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

12. 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

13. This leads to evaporative cooling
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.

14. 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

15. Gas
Liquid
Solid

16. Hydrogen bonds are stable Hydrogen bonds constantly break and re-form
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.

17. Frozen water floats (left) and frozen benzene sinks (right)
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

18. Ice fishing
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

19. Water is a Versatile Solvent
Also known as the “Universal solvent”.
Polar substances are enveloped by hydration spheres.
“Like dissolves like!”

20. 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.

21. Properties of Water
Quiz
Wiz

22. Properties of Water
A molecule in which the charges are unevenly distributed is called a
polar molecule.
cohesive molecule.
hydrogen molecule.
covalent molecule.

23. Properties of Water Hydrogen bonds between water molecules result from2
Hydrogen bonds between water molecules result from
adhesion between water molecules.
magnetic attractions between water molecules.
uneven electron distribution in each water molecule.
ionic bonds in the water molecule.

24. Acknowledgements
Unless otherwise noted, illustrations are credited to Prentice Hall and have been borrowed from Biology by Miller and Levine, © 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.

25. Acids, Bases, and pH
Ch. 2
Ms. Haut

26. 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

27. Solutions and Suspensions
Two types of mixtures can be made with water
Solutions
Suspensions

28. 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

29. 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.
When an ionic compound such as sodium chloride is placed in water, water molecules surround and separate the positive and negative ions.

30. Solutions and 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

31. 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.

32. Acids, Bases, and pH Acids, Bases, and pH H20  H+ + OH-
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.

33. 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
concentration of H+ ions greater than OH- ions
Neutral
7.0
concentration of H+ ions and OH- ions is equal.
Base
concentration of H+ ions less than OH- ions

34. 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.

35. 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.

36. (Higher concentration of H+) (Lower concentration of H+)
pH scale
Acidic solution
Neutral solution
Basic solution
(Higher concentration of H+)
Increasingly ACIDIC
(Lower concentration of H+)
Increasingly BASIC
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–
The pH scale
Each pH unit represents a tenfold change in concentration of H+
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

37. pH Indicators Cabbage Juice
Boiled cabbage creates a bluish/purplish juice that can be used to test pH of substances

38. pH Indicators Cabbage juice responds like litmus paper
Indicator turns:
Red in Acids
Blue in Bases

39. pH Indicators pH paper phenolphthalein -turns pink in presence of base

40. 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!)

41. 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

42. 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.

43. 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.

44. Acids, Bases, and pH
Quiz
Wiz

45. Acids, Bases, and pH A dissolved substance is called a solvent.1
A dissolved substance is called a
solvent.
solution.
solute.
suspension.

46. Acids, Bases, and pH 2
A compound that removes ions from a solution is called a(an)
base.
buffer.
acid.
salt.

47. Acids, Bases, and pH 3
On a pH scale, a value of 2 means that the solution has
equal concentrations of H+ and OH- ions.
the same concentration of H+ ions as pure water.
higher concentration of H+ than in pure water.
lower concentration of H+ than in pure water.

48. 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?
6 times more acidic
1,000,000 times more acidic
60 times more acidic
1,000 times more acidic

49. Acknowledgements
Unless otherwise noted, illustrations are credited to Prentice Hall and have been borrowed from Biology by Miller and Levine, © 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.