Deck 2: Water: the Medium of Life

Question 1

Amphiphilic (amphipathic) molecules include:

A) sugars.
B) acidic amino acids.
C) inorganic salts.
D) water.
E) salts of fatty acids.

Answer 1

E

Question 2

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.

Answer 2

E

Question 3

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

Answer 3

B

Question 4

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.

Question 5

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.

Question 6

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

Question 7

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

Question 8

All are examples of weak electrolytes EXCEPT:

A) hydrochloric acid.
B) acetic acid.
C) lactic acid.
D) phosphoric acid.
E) carbonic acid.

Question 9

Which of the following pairs would be the best buffer at pH 10.0?

A) Acetic acid and sodium acetate (pK_a = 4.76)
B) H₂CO₃ and NaHCO₃ (pK_a values are 3.77 and 10.4)
C) Lactic acid and sodium lactate (pK_a = 3.86)
D) NaH₂PO₄ and Na₂HPO₄ (pK_a values are 2.1, 7.2, 12.4)
E) Sodium succinate and succinic acid (pK_a = 4.21)

Question 10

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

Question 11

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.

Question 12

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 pK_a 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

Question 13

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

Question 14

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.

Question 15

If 0.1 moles of Na₂HPO₄ and 0.1 moles of NaH₂PO₄ are mixed in water, what is the resulting pH? The pK_a 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

Question 16

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.

Question 17

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

Question 18

The solvent with the highest dielectric constant in this group is:

A) water.
B) acetic acid.
C) ethanol.
D) hexane.
E) benzene.

Question 19

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

Question 20

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

Question 21

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 pK_a values.
E) buffer where the amounts of conjugate base are nearly equivalent to the amounts of weak acid.

Question 22

Aspirin contains a carboxylic acid with a pK_a 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

Question 23

Buffer systems are effective when the pH values are within ____ pH unit(s) of the pK_a value.

A) 1
B) 2
C) 3
D) 4
E) 5

Question 24

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.

Question 25

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

Question 26

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.

Question 27

Which of the following weak acids would make the best buffer at pH = 5.0?

A) acetic acid (K_a = 1.74 × 10−⁵, pK_a = 4.76)
B) H₂PO₄− (K_a = 1.38 × 10−⁷, pK_a = 7.20)
C) bicarbonate (K_a = 6.3 × 10−¹¹, pK_a = 10.24)
D) tris-hydroxymethyl aminomethane (K_a = 8.32 × 10−⁹, pK_a = 8.07)
E) lactic acid (K_a = 1.38 × 10−⁴, pK_a = 3.86)

Question 28

Which of the following would be the conjugate acid of hydrogen phosphate, HPO₄^-2?

A) H₂PO₄^-
B) H₃PO₄
C) H₂PO₄^-2
D) H₂PO₄^-
E) none of the above

Question 29

A weak acid is 33% dissociated at pH 5.0. What is the pK_a for this acid?

A) 4.5
B) 4.7
C) 5.3
D) 5.5
E) cannot be determined from the information provided

Question 30

When preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pK_a = 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

Question 31

​Discuss the dielectric constant of water. Write the equation used to calculate the dielectric constant.

Question 32

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−

Question 33

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.
B) The more linear the bond, the stronger the interaction.
C) The acceptor is a fairly electronegative atom containing a nonbonding pair of electrons.
D) It is a type of noncovalent bond.
E) All of the above statements are true about the nature of the hydrogen bond.

Question 34

pH = pK_a when:

A) [A−]/[HA] = 0
B) log ([A−]/[HA]) = 1
C) [A−] >> [HA]
D) [A−] = [HA]
E) log ([HA]/[A−]) = 1

Question 35

If a weak acid is 25% deprotonated at pH 4, what would the pK_a be?

A) 3.40
B) 3.52
C) 4.48
D) 4.60
E) cannot determine from given information

Question 36

What ionic form(s) is/are most prevalent at pH 7.0? The pK_a values of phosphoric acid are 2.1, 7.2, and 12.4.

A) HPO₄−²
B) H₂PO₄−
C) HPO₄−² and PO₄−³
D) H₂PO₄− and HPO₄−²
E) All are correct

Question 37

Calculate the equilibrium constant, K_eq, for 1 L of pure water.​

Question 38

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
B) 3.16 × 10³
C) 0.54
D) 1.90
E) cannot be determined based upon the provided information

Question 39

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 (K_a = 1.38 × 10−⁴, pK_a = 3.86)
B) bicarbonate (K_a = 6.3 × 10−¹¹, pK_a = 10.24)
C) acetic acid (K_a = 1.74 × 10−⁵, pK_a = 4.76)
D) succinate (K_a = 2.34 × 10−⁶, pK_a = 5.63)
E) tris-hydroxymethyl aminomethane (K_a = 8.32 × 10−⁹, pK_a = 8.07)

Question 40

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−].

Question 41

Explain weak electrolytes with an example.​

Question 42

Explain the role that water plays in living systems.​

Question 43

Discuss the Phosphate Buffer System in living systems.​