1. Water’s life supporting properties. Acids and bases.
Life Science I Dr. Ekaterina (Kate) Vorotnikova Office: 413b
Lecture 4
Water’s life supporting properties. Acids and bases.
(pages 23-30)

2. Assignments for a 2/01 week:
Lec 3 Assignment- starts 2/01
2. Lec 4 Assignment-starts 2/03
3. Work on LearnSmart study modulus to study chapter 2 – starts 2/01
4. Quiz 2 –starts 2/05
Due on Monday Feb. 8 at 11:00 p.m.!!!!

3. Water’s Importance to Life
Life began in water.
Single most important molecule on Earth
All organisms are 70-90% water.
Water has unique properties that make it a life-supporting substance.
Properties stem from structure of molecule

4. How Long Can You Live Without Water?
Max Daily Temperature
Number of Days in the Shade
No Water
1 Quart .95 Liter
2 Quarts 1.90 Liters
4 Quarts 3.79 Liters
10 Quarts 9.46 Liters
20 Quarts Liters
120 F / 48.9 C
2 days 2
2.5 3
4.5
110 F / 43.3 C
3.5 4 5 7
100 F / 37.8 C
5.5 6
9.5
13.5
90 F / 32.2 C 8 9
10.5 15 23
80 F / 26.7 C 10 11 13 19 29
70 F / 21.1 C 12 14
20.5 32
60 F / 15.6 C 21
50 F / 10.0 C
14.5

6. Structure of water Polar covalent bond
Atoms do not share electrons equally.
Oxygen is more electronegative than hydrogen.
Electrons spend more time around oxygen nucleus than hydrogen nuclei.
Oxygen end becomes slightly negative/ hydrogens become slightly positive - NOT an ionic bond or ions
Hydrogen bond – slightly positive hydrogen of one water molecule attracted to slightly negative oxygen in another water molecule

7. Properties of water that support life
Solvency
Cohesion and adhesion
High surface tension
High heat capacity
High heat of vaporization
Varying density

8. The salt NaCl dissociates in water.
Water is a solvent.
Due to polarity and H-bonding, water dissolves many substances.
Hydrophilic – molecules attracted to water
Hydrophobic – molecules not attracted to water
Water causes NaCl to dissociate. + + – H H O O H H + + –
Na+
Cl–
The salt NaCl dissociates in water.

9. Contributes to water transport in plants
Cohesion
Ability of water molecules to cling to each other due to hydrogen bonding
Adhesion
Ability of water molecules to cling to other polar surfaces
Allows water to be excellent transport system in and outside of living organisms.
Contributes to water transport in plants

11. Water has a high surface tension.
Water molecules at the surface cling more tightly to each other than to the air above.
Mainly due to hydrogen bonding
Surface tension allows a water strider to walk on water

12. Water’s hydrogen bonds moderate temperature
Because of hydrogen bonding, water has a greater ability to resist temperature change than other liquids
Heat is the energy associated with movement of atoms and molecules in matter
Temperature measures the intensity of heat
Heat must be absorbed to break hydrogen bonds; heat is released when hydrogen bonds form
Student Misconceptions and Concerns
1. Students are unlikely to have carefully considered the four special properties of water that are apparent in our world. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for examples of each of these properties in each student’s experiences will require reflection and may produce meaningful illustrations. Similarly, quizzes or exam questions matching examples to a list of the properties requires high-level evaluative analysis.
2. Students at all levels struggle with the distinction between heat and temperature. Students might also expect that all ice is about the same temperature, 0°C. Redefining and correcting misunderstandings often takes more class time and energy than introducing previously unknown concepts.
Teaching Tips
1. Have students compare the seasonal ranges of temperatures of Anchorage and Fairbanks, Alaska. (Many websites, such as provide weather information about various cities.) These two northern cities have large differences in their annual temperature ranges. Make the point that the coastal location of Anchorage moderates the temperature.
2. The following analogies may help students to understand the relation between evaporation, heat, and temperature. (a) Ask students how the average on an exam would be affected if the brightest students didn’t take the test. (b) The authors note that the performance of a track team would drop if the fastest sprinters did not compete. In both analogies, removing the top performers lowers the average, just like the evaporation of the most active water molecules cools the evaporative surface.
3. It’s not the heat, it’s the humidity. The efficiency of evaporative cooling is affected by humidity. As humidity rises, the rate of evaporation decreases, making it more difficult to cool our heat-generating bodies on a warm and humid summer day.
Copyright © 2009 Pearson Education, Inc.

13. High heat of vaporization
High heat capacity
The many hydrogen bonds linking water molecules allow water to absorb heat without greatly changing its temperature.
Temperature of water rises and falls slowly.
High heat of vaporization
Takes a great deal of energy to break H bonds for evaporation
Heat is dispelled as water evaporates.

15. Water can exist as a gas, liquid, and solid
Water is less dense as a solid, a property due to hydrogen bonding
When water freezes, each molecule forms a stable hydrogen bond with four neighbors
A three-dimensional crystal results
There is space between the water molecules
Ice is less dense than water, so it floats

16. Water is more dense than ice.
Unlike other substances, water expands as it freezes.
Ice properties
Ice floats rather than sinks.
It makes life possible in water.
Ice acts as an insulator

17. ice lattice Density (g/cm3) Temperature (ºC) liquid water ice layer
1.0
Density (g/cm3)
0.9 4
100
Temperature (ºC)
ice layer
Protists provide
food for fish.
River otters visit
ice-covered ponds.
Aquatic insects survive
in air pockets.
Freshwater
fish take
oxygen
from water.
Common frogs and pond turtles hibernate.

19. Acids and Bases
Water dissociates into an equal number of hydrogen ions (H+) and hydroxide ions (OH-)
Dissociation of water molecules
OH– H+ H H O H H O
OH– H H O H+
H – O – H
H OH–
water
hydrogen
ion
hydroxide
ion

20. Acids HCl H+ + Cl- Hydrochloric acid
Common examples are lemon juice, vinegar, tomatoes, and coffee.
Substances that dissociate in water, releasing H+ ions
Adding an acid to water increases the number of H+ ions.
Addition of hydrochloric acid (HCl)
HCl H+
OH–
HCl H+ + Cl-
Hydrochloric acid H H O H H
Cl– O H+ H+
OH– H H
Cl– O H+

21. Bases NaOH Na+ + OH- Sodium hydroxide
Common bases are ammonia and milk of magnesia.
Substances that either take up hydrogen ions or release hydroxide ions
Adding a base to water either increases the number of OH- ions or decreases the number of H+ ions.
Addition of sodium hydroxide (NaOH), a base
NaOH H H
OH–
NaOH Na+ + OH-
Sodium hydroxide O H H O
Na+ H+
OH–
OH–
Na+ H H H+ O
OH–

22. pH Mathematical way to indicate number of hydrogen ions in solution
The pH scale pH
Mathematical way to indicate number of hydrogen ions in solution
pH scale ranges from 0 to 14
pH below 7 acidic – more [H+] than [OH-]
pH above 7 basic – more [OH-] than [H+]
pH of 7 neutral – [H+] equal to [OH-]

23. Buffer
Chemical or combination of chemicals that keeps pH within normal limits
Resist pH change by taking up excess H+ or OH-
pH of blood is about 7.4 – maintained by buffer

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25. The burning of gasoline leads to acid deposition which causes:
(a) Trees to die
(b) statues to deteriorate