1. Water, Water, Everywhere (Ch. 3)

2. Why are we studying water?
More about Water
Why are we studying water?
All life occurs in water
inside & outside the cell

3. Chemistry of water Water is polar molecule
remember polar covalent bonds
+ & – poles

4. Chemistry of water H2O molecules form H-bonds with each other
+H attracted to –O
creates a sticky molecule
APBio/TOPICS/Biochemistry/Movies AP/hydrogenbonds-Thinkwell.swf

5. Elixir of Life Special properties of water 1. cohesion & adhesion
surface tension, capillary action
2. good solvent
many molecules dissolve in H2O
hydrophilic vs. hydrophobic
3. lower density as a solid
ice floats!
4. high specific heat
water stores heat
5. high heat of vaporization
heats & cools slowly
Ice! I could use more ice!

6. Cohesion H bonding between H2O creates cohesion water is “sticky”
surface tension
Property of liquid that allows it to resist external force
Caused by the attraction of particles
drinking straw
can you suck sugar up a straw?

7. Adhesion H2O molecules form H bonds with other substances
capillary action
meniscus
water climbs up fiber
ex. paper towel

8. How does H2O get to top of trees?
Transpiration is built on cohesion & adhesion
APBio/TOPICS/04Biochemistry/MoviesAP/03_03WaterTransport_A.swf

9. 2. Water is the solvent of life
Polarity makes H2O a good solvent
polar H2O molecules surround +&–ions
solvents dissolve solutes creating solutions
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

10. What dissolves in water?
Hydrophilic
substances have attraction to H2O
polar or non-polar?
ionic
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

11. What doesn’t dissolve in water?
Hydrophobic
substances that don’t have an attraction to H2O
polar or non-polar?
Oh, look hydrocarbons!
fat (triglycerol)
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

12. And this has made all the difference!
3. The special case of ice
Most (all?) substances are more dense when they are solid, but not water…
Ice floats!
H bonds form a crystal
And this has made all the difference!

13. Ice floats

14. Why is “ice floats” important?
Oceans & lakes don’t freeze solid
surface ice insulates water below
allowing life to survive the winter
if ice sank…
ponds, lakes & even oceans would freeze solid
in summer, only upper few inches would thaw
seasonal turnover of lakes
sinking cold H2O cycles nutrients in autumn

15. 4. Specific heat H2O resists changes in temperature
high specific heat
takes a lot to heat it up
takes a lot to cool it down
H2O moderates temperatures on Earth (and in our bodies!!)

16. Specific heat & climate

17. 5. Heat of vaporization

18. Evaporative cooling
Organisms rely on heat of vaporization to remove heat

19. Water forms ions H2O  H+ + OH–
Hydrogen ion (H+) splits off (dissociates) from water to leave a hydroxide ion (-OH)
H > H OH
If concentration of 2 ions is equal, water is neutral
If [H+] > [-OH], water is acidic
If [-OH] > [H+], water is basic
pH scale = how acidic or basic a solution is
H2O  H+ + OH–

20. pH Scale
In pure water only 1 water molecule in every 554 million is dissociated.
very small amount of ions
[H+] or [OH-] is 10-7M
[H+] [OH-] = 10-14
pH scale is based on this equation
Exercise = acidic in muscles
CO2 = carbonic acid
lactic acid
body uses buffers to counter act this

21. pH Scale In neutral solution [H+] = 10-7  pH = 7
Values for pH decline as [H+] increase
Acids
adding acid increases [H+]
Bases
adding base increases [OH-]

22. pH & Biology pH of a neutral solution = 7
Acidic solutions = pH < 7 Basic solutions = pH > 7
Most biological fluids have pH 6 – 8
pH values in human stomach can reach 2
Each pH unit represents a 10-fold difference in H+ & OH- concentrations.
small change in pH actually indicates a substantial change in [H+] & [OH-]

23. tenfold change in H+ ions
pH Scale
10–1
H+ Ion
Concentration
Examples of Solutions
Stomach acid, Lemon juice 1 pH
100
Hydrochloric acid
10–2 2
10–3
Vinegar, cola, beer 3
10–4
Tomatoes 4
10–5
Black coffee, Rainwater 5
10–6
Urine, Saliva 6
10–7
Pure water, Blood 7
10–8
Seawater 8
10–9
Baking soda 9
10–10
Great Salt Lake 10
10–11
Household ammonia 11
10–12
Household bleach 12
10–13
Oven cleaner 13
10–14
Sodium hydroxide 14
tenfold change in H+ ions
pH1  pH2
10-1 10-2
10 times less H+
pH8  pH7
10-8 10-7
10 times more H+
pH10  pH8
10-10 10-8
100 times more H+
In pure water only 1 water molecule in every 554 million is dissociated

24. Buffers & cellular regulation
pH of cells must be kept ~7
pH affects shape of molecules
shape of molecules affect function
pH affects cellular function
Control pH by buffers
reservoir of H+
donate H+ when [H+] falls
absorb H+ when [H+] rises 1 2 3 4 5 6 7 8 9
Amount of base added
Buffering
range pH
Exercise = acidic in muscles
CO2 = carbonic acid
lactic acid
body uses buffers to counter act this

25. Any Questions? Do one brave thing today…then run like heck!
He’s gonna earn a Darwin Award!
Any Questions?
Do one brave thing today…then run like heck!

26. Review Questions

27. A. The following are pH values: cola-2; orange juice-3; beer-4; coffee-5; human blood-7.4. Which of these liquids has the highest molar concentration of OH-?
cola
orange juice
beer
coffee
human blood
Answer: e
Source: Taylor - Student Study Guide for Biology, Sixth Edition, Test Your Knowledge Question #18

28. C. If the pH of a solution is increased from pH 8 to pH 9, it means that the
concentration of H+ is 10 times greater than what it was at pH 8.
concentration of H+ is 100 times less than what it was at pH 8.
concentration of OH- is 10 times greater than what it was at pH 8.
concentration of OH- is 100 times less than what it was at pH 8.
concentration of H+ is greater and the concentration of OH- is less than at pH 8.
Answer: c
Source: Barstow - Test Bank for Biology, Sixth Edition, Question #43

29. D. Acid precipitation has lowered the pH of a particular lake to 4
D. Acid precipitation has lowered the pH of a particular lake to 4.0. What is the hydroxide ion concentration of the lake?
10-7M
10-4M
10-10M
10-14M
10 M
Answer: c
Source: Campbell/Reece - Biology, Sixth Edition, EOC Self-Quiz Question #10
Discussion Notes for the Instructor
To answer this question students need to know the relationship between pH and hydroxide concentration.