AP BIOLOGY NAME_____________________

BIOCHEMISTRY
Unit 2 Part 3 ACTIVITY #2 (Chapter 3) DATE___________PERIOD_____

WATER, ACIDS, BASES, BUFFERS

STRUCTURE AND GEOMETRY OF WATER:

W

Unit 2 Part 3 Biochemistry Activity #2 page 1 of 9

 PROPERTIES OF WATER:
Liquid water is cohesive

Cohesion = H bonds between water molecules; H2O molecules tend to

stick together.
Importance = Transport H2O against gravity in plants
Higher surface tension
Water has a high specific heat

Takes a lot of energy to raise 1 gram of H2O 1 oC

Why? Must break H bonds
Liquid H2O can absorb large amounts of heat with small changes in
temperature
Water has a high heat of vaporization

Takes a lot of energy to convert liquid H2O into vapor

Why? Must break H bonds
Keeps water in liquid state

Water expands with it freezes

Solid H2O is less dense than liquid H2O

Why? In solid state H2O locked into max. number of H bonds; takes up
more space

Water is a versatile solvent

Will dissolve polar covalent and ionic compounds

Unit 2 Part 3 Biochemistry Activity #2 page 2 of 9

DISSOCIATION OF WATER:

H2O + H2O  H3O+ + OH-

H2O   H+ + OH-

Hydronium ion Hydroxide ion

1 out of 554,000,000 water molecules dissociates

At equilibrium in pure water at 25oC

[H+] = [OH-] = 1.0 x 10-7 M

If add [H+] to pure water If add [OH-] to pure water

Removes OH- Removes H+
Equilibrium shifts left Equilibrium shifts right
[H+] > [OH-] [OH-]>[H+]
reduces H+ indirectly
If add NH3
NH3 + H+ 
NH4+
Reduces H+ directly

PH SCALE:
pH = -log10[H+] [H+] x [OH-] = 10-14
if [H+] = 10-7 If [H+] = 10-9
then pH = 7 Then [OH-] = 10-5
pOH=5 and pH = 9

Unit 2 Part 3 Biochemistry Activity #2 page 3 of 9

BUFFERS:
Description Function Importance

Weak acids or bases Minimize changes in Controls chemical

pH reactions

Maintains homeostasis

BICARBONATE BUFFER SYSTEM:

H2O + CO2   H2CO3  HCO3— + H+

HCO3- = Bicarbonate (weak base)

H2CO3 = Carbonic acid (weak acid)

Major buffer system in blood

Maintains blood pH between 7.38 and 7.42

Action: Effect:
Increase [H+]Increase [H+]
How? Equilibrium shifts left
Fat H+ + HCO3-  H2CO3  CO2 + H2O
metabolism Increase [CO2]
OD on acidic Increase rate and depth of respiration
drug

Increase Rate & Decrease [CO2]

Depth of Respiration
Equilibrium shifts left
H+ + HCO3-  H2CO3  CO2 + H2O
Hyperventilate
Blood pH increases

Unit 2 Part 3 Biochemistry Activity #2 page 4 of 9

QUESTIONS:
3.1
1. Explain why water is a polar molecule.

_________________________________________________________________________________________

_________________________________________________________________________________________

2. Explain how water is able to form 4 hydrogen bonds.

___________________________________________

___________________________________________

___________________________________________

_________________________________________________________________________________________

3. Add + and – signs to indicate the charged regions of each water molecule above. Then, indicate the
hydrogen bonds.
3.2
4. List the 5 emergent properties of water.

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

5. Define the following terms.

Cohesion

Adhesion

Unit 2 Part 3 Biochemistry Activity #2 page 5 of 9

6. Why is water cohesive?

_________________________________________________________________________________________

_________________________________________________________________________________________

7. What is the biological importance of water’s cohesive and adhesive properties?

_________________________________________________________________________________________

_________________________________________________________________________________________

8. Why does water have a greater degree of surface tension than most other liquids?

_________________________________________________________________________________________

_________________________________________________________________________________________

9. Why does water have a high specific heat?

_________________________________________________________________________________________

_________________________________________________________________________________________

10. What is the biological importance of water’s high specific heat?

_________________________________________________________________________________________

_________________________________________________________________________________________

11. Why does water have a relatively high heat of vaporization?

_________________________________________________________________________________________

_________________________________________________________________________________________

12. What is the biological importance of water’s relatively high heat of vaporization?

_________________________________________________________________________________________

_________________________________________________________________________________________

Unit 2 Part 3 Biochemistry Activity #2 page 6 of 9

13. Why does water expand when it freezes?

_________________________________________________________________________________________

_________________________________________________________________________________________

14. Why does ice float?

_________________________________________________________________________________________

15. What is the biological importance of the expansion of water when it freezes?

_________________________________________________________________________________________

_________________________________________________________________________________________

16. Match the description/definition with the correct term.

A. Aqueous solution D. Solute

B. Hydrophilic E. Solution
C. Hydrophobic F. Solvent

______ Homogenous mixture of 2 or more substances

______ Dissolving agent

______ Material being dissolved

______ Solution where water is solvent

______ Water loving; molecules with an affinity for water

______ Water fearing; molecules that do not have an affinity for water

17. Why is water a versatile solvent?

_________________________________________________________________________________________

_________________________________________________________________________________________

18. In general, what kinds of materials will not dissolve in water?

________________________________________________________________________________________

Unit 2 Part 3 Biochemistry Activity #2 page 7 of 9

3.3
19. At equilibrium in pure water at 25oC:

a. How does the [H+] compare to the [OH]? _________________________

b. What is the [H+]? ____________________________________________

20. Each of the following will affect the equilibrium established in pure water during the dissociation of
water. Describe what effect each will have on the equilibrium by completing the following chart.

Direction
Addition of: Effect on [H+] Effect on [OH-]
Equilibrium Shifts
H2SO4

KOH

NH3

21. How does the [H+] compare to the [OH-] in each of the following:

a. A neutral solution: _________________________________________

b. An acidic solution: _________________________________________

c. A basic solution: __________________________________________

20. Complete the following chart.

[H+] pH [OH-] pOH

10-2

10-4

21. What is the pH range for most biological fluids? _______________________

What fluid is the exception to this range? ____________________________

Unit 2 Part 3 Biochemistry Activity #2 page 8 of 9

22. A patient has been vomiting for a prolonged period of time.

a. What effect would this have on the [H+] in the blood? _____________

b. How will the bicarbonate buffer system respond to this change?

___________________________________________________________________________

c. What effect will the buffer system response have on the rate of respiration?

___________________________________________________________________________

d. If the buffer system does not return the blood pH to within the normal range or if the vomiting
continues, how will the kidneys respond?

Will the kidneys excrete or reabsorb H+?________________________

Will the kidneys excrete or reabsorb HCO3—?_____________________

End of Chapter Synthesis and Evaluation Problems

Do problems 1-3, 5 and 16. Check and correct your answers to 1-3, 5
1._________
2._________ ***Question #16 needs to be typed out, then answered in no
3._________ more and no less than 100 to 150 words. Turn in separately
5._________ to the tray. This is worth 20 points. Do not plagiarize. Use
your own words and thoughts…but, use vocabulary terms and
ideas taught in this chapter!

Study Guide/ISN (20 points)

In your study guide book, review pages 35-37. In your ISN, do the following: Title the page Chapter 3 Water and
Life Must Know! In one color, copy down each of the must know items listed on page 34 in study guide leaving space
underneath each to include in a different color a brief description, diagram, model or mnemonic device that will help
you study for the unit test and more importantly the AP test in May.

Bozeman Science/Podcasts/ISN (See syllabus for format) (20 points)

1. Amoeba Sisters Properties of water
2. Bozeman Acids, Bases and pH.

Unit 2 Part 3 Biochemistry Activity #2 page 9 of 9