Chapter 2—Water: The Medium of Life
MULTIPLE CHOICE
1. Properties of water that render it so suited to its role as a medium of life include all EXCEPT:
a.
Unrivaled ability to form hydrogen bonds.
b.
Unusually high dielectric constant of water explains water’s ability to surround ions and
increase the ions’ attraction for one another.
c.
Unparalleled ability to orient around nonpolar solutes to promote hydrophobic
interactions.
d.
The small, but significant, tendency to form H+ and OH− ions.
e.
None, all are true.
2. All are true for water for a substance of its molecular weight that is neither metallic nor ionic
EXCEPT:
a.
a high surface tension.
b.
a chemically inert solvent, which has a great capacity to dissolve a diverse spectrum of
molecules and ions.
c.
a positive volume of melting.
d.
a high dielectric constant.
e.
a high capacity to form hydrogen bonds
3. The unrivaled ability to form ____ hydrogen bonds per liquid water molecule is the source of the
strong intermolecular attractions unique to water.
a.
1
b.
2
c.
3
d.
4
e.
5
4. Because of its highly polar nature, water is an excellent solvent for polar substances, but NOT for:
a.
salts.
b.
sugars.
c.
aldehydes and ketones.
d.
hydrocarbons.
e.
alcohols and amines.
5. The solvent with the highest dielectric constant in this group is:
a.
water.
b.
acetic acid.
c.
ethanol.
d.
hexane.
e.
benzene.
6. Hydrogen bonds in ice are all EXCEPT:
a.
directional.
b.
straight.
c.
weak.
d.
responsible for the lower density of ice over liquid water.
e.
holding water molecules in ice apart.
7. Pure liquid water consists of H2O molecules:
a.
held in a rigid three-dimentional network.
b.
with local preference for linear geometry.
c.
with large numbers of strained or broken hydrogen bonds.
d.
which do not switch H-bonds readily.
e.
all are true.
8. The average lifetime of a hydrogen bond connection in water is on the order of 10:
a.
picoseconds.
b.
microseconds.
c.
milliseconds.
d.
seconds.
e.
nanoseconds.
9. The ____ bonding of water with the polar functional groups on nonionic polar solutes such as sugars
are ____ than the intermolecular attractions between solute molecules allowing solute molecules to
readily dissolve in water.
a.
ionic, stronger
b.
hydrogen, weaker
c.
hydrophobic, stronger
d.
hydrogen, stronger
e.
ionic, weaker
10. The H-bonded water around an ionic substance tends to ____; and the H-bonded water around
nonpolar solutes tends to ____.
a.
inhibit ionization, promote hydrophobic interactions
b.
inhibit ionization, inhibit hydrophobic interactions
c.
not impact ionization, inhibit hydrophobic interactions
d.
promote ionization, not impact hydrophobic interactions
e.
promote ionization, promote hydrophobic interactions
11. Amphiphilic (amphipathic) molecules include:
a.
sugars.
b.
acidic amino acids.
c.
inorganic salts.
d.
water.
e.
salts of fatty acids.
12. In micelles:
a.
polar ends form hydrophobic interactions with water.
b.
nonpolar ends form hydrophilic interactions with water.
c.
hydrocarbon tails form hydrophobic interactions with water.
d.
polar ends are hydrophobic and nonpolar ends are hydrophilic.
e.
hydrocarbon tails are excluded from the water into hydrophobic domains.
13. By limiting the orientation that neighboring water molecules can assume, solutes give ____ to the
solvent and ____ the dynamic interplay among H2O molecules that occurs in pure water.
a.
pressure, disrupt
b.
disorder, increase
c.
disorder, decrease
d.
order, diminish
e.
order, increase
14. To ____ the osmotic pressure created by the contents of their cytosol, cells tend to store substances
such as amino acids and sugars in ____ form.
a.
increase, monomeric
b.
minimize, polymeric
c.
minimize, monomeric
d.
maximize, polymeric
e.
increase, polymeric
15. Water ionizes because:
a.
the smaller electronegative oxygen atom strips the electron from one of its hydrogen
atoms, leaving the proton to dissociate.
b.
the larger electronegative oxygen atom strips the electron from one of its hydrogen atoms,
leaving the proton to dissociate.
c.
the smaller electropositive oxygen atom strips the electron from one of its hydrogen
atoms, leaving the proton to dissociate.
d.
the larger electropositive oxygen atom strips the electron from one of its hydrogen atoms,
leaving the proton to dissociate.
e.
None of the above
16. Grapefruit juice at pH 3.2 contains about ____ times as much H+ as orange juice at pH 4.3.
a.
0.9
b.
10−7.5
c.
10−2
d.
12
e.
101
17. All are examples of weak electrolytes EXCEPT:
a.
hydrochloric acid.
b.
acetic acid.
c.
lactic acid.
d.
phosphoric acid.
e.
carbonic acid.
18. If 0.1 moles of Na2HPO4 and 0.1 moles of NaH2PO4 are mixed in water, what is the resulting pH? The
pKa values for phosphoric acid are 2.1, 7.2, 12.4.
a.
2.1
b.
4.65
c.
7.2
d.
9.8
e.
12.4
19. Estimate the pH of the resulting solution prepared by mixing 1.0 mole of solid disodium phosphate
(Na2HPO4) and 1.25 mole of hydrochloric acid. The pKa values for phosphoric acid are 2.1, 7.2, 12.4.
a.
pH < 2.1
b.
pH = 2.1
c.
2.1 < pH < 7.2
d.
pH = 7.2
e.
7.2 < pH < 12.4
20. Which of the following pairs would be the best buffer at pH 10.0?
a.
Acetic acid and sodium acetate (pKa = 4.76)
b.
H2CO3 and NaHCO3 (pKa values are 3.77 and 10.4)
c.
Lactic acid and sodium lactate (pKa = 3.86)
d.
NaH2PO4 and Na2HPO4 (pKa values are 2.1, 7.2, 12.4)
e.
Sodium succinate and succinic acid (pKa = 4.21)
21. What ionic form(s) is/are most prevalent at pH 7.0? The pKa values of phosphoric acid are 2.1, 7.2,
12.4.
a.
HPO4−2
b.
H2PO4−
c.
HPO4−2 and PO4−3
d.
H2PO4− and HPO4−2
e.
All are correct
22. A plasma pH of 6.8 doesn’t seem too far away from a normal pH of 7.4, but at pH 6.8 the H+
concentration is ____ times greater than at pH 7.4 and results in severe acidosis.
a.
0.1
b.
0.6
c.
4
d.
10
e.
20
23. pH = pKa when:
a.
[A−]/[HA] = 0
b.
log ([A−]/[HA]) = 1
c.
[A−] >> [HA]
d.
[A−] = [HA]
e.
log ([HA]/[A−]) = 1
24. Buffers have all of the following characteristics EXCEPT:
a.
they have relatively flat titration curves at the pH(s) where they buffer.
b.
they resist changes in their pH as acid or base is added.
c.
they are typically composed of a weak acid and its conjugate base.
d.
they buffer best for polyprotic acids half-way between the two pKa values.
e.
buffer where the amounts of conjugate base are nearly equivalent to the amounts of weak
acid.
25. Buffer systems are effective when the pH values are within ____ pH unit(s) of the pKa value.
a.
1
b.
2
c.
3
d.
4
e.
5
26. Intracellular pH is maintained primarily by the ____ and ____ buffer systems, and the extracellular pH
by the ____ buffer system.
a.
HPO42−/H2PO4−; HCO3−/H2CO3; histidine
b.
H3PO4/H2PO4−; histidine; HCO3−/H2CO3
c.
HCO3−/H2CO3; H3PO4/H2PO4−; histidine
d.
HPO42−/H2PO4−; histidine; HCO3−/H2CO3
e.
HCO3−/H2CO3; histidine; H3PO4/H2PO4−
27. Hyperventilation is a physiological mechanism to:
a.
lower [CO2 (g)] in the blood and increase blood pH.
b.
raise [CO2 (g)] in the blood and increase blood pH.
c.
lower [CO2 (g)] in the blood and decrease blood pH.
d.
raise [CO2 (g)] in the blood and decrease blood pH.
e.
lower [CO2 (g)] in the blood and increase [HCO3−].
28. Water is particularly suited as a solvent for biosystems because it has all of the following
characteristics EXCEPT:
a.
Water is a medium for ionization enhancing the variety of chemical species.
b.
Water is innocuous, yet a powerful solvent.
c.
Water is an excellent solvent for nonpolar substances.
d.
Water is relatively chemically inert, yet dissolves a variety of solutes.
e.
Through hydrophobic interactions, lipids coalesce into membranes in water.
29. Which of the following weak acids would make the best buffer at pH = 5.0?
a.
acetic acid (Ka = 1.74 10−5, pKa = 4.76)
b.
H2PO4− (Ka = 1.38 10−7, pKa = 7.20)
c.
bicarbonate (Ka = 6.3 10−11, pKa = 10.24)
d.
tris-hydroxymethyl aminomethane (Ka = 8.32 10−9, pKa = 8.07)
e.
lactic acid (Ka = 1.38 10−4, pKa = 3.86)
30. The enzyme fumarase has a pH optimum of about 7.6. What would be the buffer of choice to study
this enzyme?
a.
lactic acid (Ka = 1.38 10−4, pKa = 3.86)
b.
bicarbonate (Ka = 6.3 10−11, pKa = 10.24)
c.
acetic acid (Ka = 1.74 10−5, pKa = 4.76)
d.
succinate (Ka = 2.34 10−6, pKa = 5.63)
e.
tris-hydroxymethyl aminomethane (Ka = 8.32 10−9, pKa = 8.07)
31. When preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pKa = 4.8) and
sodium acetate, the volume of acetic acid needed would be ____ the volume of sodium acetate
solution.
a.
equal to
b.
less than half of
c.
more than half of
d.
about six times
e.
about twice
32. Hypoventilation is characterized by inability to excrete CO2 rapidly enough and can be caused by all
EXCEPT:
a.
anesthetics.
b.
depressant drugs.
c.
narcotics.
d.
lung diseases.
e.
encephalitis.
33. If an abundance of an organic acid with a pKa of 3.9 is found in the bloodstream, which of the
following is true?
a.
it will be mostly protonated
b.
it will be mostly deprotonated
c.
it will form an effective buffer
d.
it will cause metabolic acidosis
e.
both b and d are correct
34. Aspirin contains a carboxylic acid with a pKa of 3.5. Which of the following is true?
a.
Aspirin will be mostly protonated in the stomach
b.
Aspirin will be mostly protonated in the bloodstream
c.
Aspirin will be easily absorbed in the stomach due to its negative charge
d.
Aspirin will be easily transported in the bloodstream due to its negative charge
e.
both a and d are correct
35. If a weak acid is 25% deprotonated at pH 4, what would the pKa be?
a.
3.40
b.
3.52
c.
4.48
d.
4.60
e.
cannot determine from given information
36. Which of the following would be the conjugate acid of hydrogen phosphate, HPO4-2?
a.
H2PO4–
d.
H2PO4–
b.
H3PO4
e.
none of the above
c.
H2PO4-2
37. Formic acid is the active agent in an ant bite. What is the ratio of base/acid for formic acid (pKa = 3.9)
in the blood stream at pH 7.4?
a.
3.16 10-4
d.
1.90
b.
3.16 103
e.
cannot be determined based upon the
provided information
c.
0.54
38. Which of the following statements is INCORRECT about the nature of the hydrogen bond
a.
The donor is a hydrogen atom bonded to
an atom that is less electronegative than
hydrogen.
d.
It is a type of noncovalent bond.
b.
The more linear the bond, the stronger the
interaction.
e.
All of the above statements are true about
the nature of the hydrogen bond
c.
The acceptor is a fairly electronegative
atom containing a nonbonding pair of
electrons.
39. A weak acid is 33% dissociated at pH 5.0. What is the pKa for this acid?
a.
4.5
d.
5.5
b.
4.7
e.
cannot be determined from the
information provided
c.
5.3