Deck 2: Water: the Medium of Life

Question 1

Which of the following compounds is included in amphiphilic molecules?

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

Answer 1

A

Question 2

Which of the following specifies the average lifetime of a hydrogen bond connection in water?

A)10 milliseconds
B)10 microseconds
C)10 nanoseconds
D)10 picoseconds

Answer 2

D

Question 3

Which of the following effects do solutes have on a water solvent?

A)They enhance the dynamic interplay among H₂O molecules.
B)They increase the orientation that neighbouring water molecules can assume.
C)They have no effect.
D)They give order to the solvent.

Answer 3

D

Question 4

How many hydrogen bonds can a single liquid water molecule make?

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

Question 5

Which of the following is the strongest type of bonding that occurs between water and the polar functional groups on non-ionic polar solutes?

A)ionic
B)hydrophobic
C)electrostatic
D)hydrogen

Question 6

Which of the following types of interactions occur between hydrogen bonded water and non-polar solutes?

A)hydrophobic
B)hydrophilic
C)ionic
D)van der Waals

Question 7

The pKₐs of phosphoric acid are 2.1,7.2,and 12.4.Which of the following values is the correct estimate of the pH of the resulting solution prepared by mixing 1.0 mole of solid disodium phosphate (Na₂HPO₄)and 1.25 moles of hydrochloric acid?

A)pH < 2.1
B)pH = 2.1
C)2.1 < pH < 7.2
D)pH = 7.2

Question 8

Which of the following explains how cells store substances such as amino acids and sugars in order to minimize the osmotic pressure created by the contents of their cytosol?

A)in monomeric form
B)in dimeric form
C)in trimeric form
D)in polymeric form

Question 9

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 (pKas are 3.77 and 10.4)
C)lactic acid and sodium lactate (pKa = 3.86)
D)NaH₂PO4 and Na2HPO4 (pKas are 2.1,7.2,12.4)

Question 10

Which of the following is NOT a property of water that renders it so suited to its role as a medium of life?

A)unrivalled ability to form hydrogen bonds
B)unusually high dielectric constant,which explains its ability to surround ions and increase the ions' attraction for one another
C)unparalleled ability to orient around non-polar solutes to promote hydrophobic interactions
D)a small,but significant,tendency to form H⁺ and OH⁻²⁻ ions

Question 11

Which of the following acids is NOT a weak electrolyte?

A)hydrochloric acid
B)acetic acid
C)lactic acid
D)phosphoric acid

Question 12

How many times more H⁺ does grapefruit juice at pH 3.2 contain compared to orange juice at pH 4.3?

A)10-7.5
B)10-2
C)0.9
D)12

Question 13

Which of the following is reason for the ionization of water?

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.

Question 14

Which of the following solvents has the highest dielectric constant?

A)water
B)acetic acid
C)ethanol
D)hexane

Question 15

Which of the following is NOT a characteristic of water?

A)high surface tension
B)high dielectric constant
C)positive volume of melting
D)high capacity to form hydrogen bonds

Question 16

Which of the following is a feature of micelles?

A)Hydrocarbon tails form hydrophobic interactions with water.
B)Polar ends form hydrophobic interactions with water.
C)Hydrocarbon tails are excluded from the water into hydrophobic domains.
D)Polar ends are hydrophobic,and non-polar ends are hydrophilic.

Question 17

Which of the following is a characteristic of pure liquid H₂O molecules?

A)They are held in a rigid 3-dimensional network.
B)They have local preference for linear geometry.
C)They have large numbers of strained or broken hydrogen bonds.
D)They do not switch H bonds readily.

Question 18

The pKₐs of phosphoric acid are 2.1,7.2,and 12.4.Which of the following values is the resulting pH if equal amounts of Na₂HPO₄ and NaH₂PO₄ are mixed in water?

A)2.1
B)4.65
C)7.2
D)9.8

Question 19

Which of the following is NOT soluble in water?

A)salts
B)sugars
C)aldehydes
D)hydrocarbons

Question 20

Which of the following is a trait of hydrogen bonds in ice?

A)weak
B)non-directional
C)straight
D)responsibility for the higher density of ice over liquid water

Question 21

A plasma pH of 6.8 does not seem too far away from a normal pH of 7.4.How many times greater is the H⁺ concentration at pH 6.8 compared to pH 7.4?

A)0.1
B)0.6
C)4
D)10

Question 22

Which of the following values is the pKa for a weak acid that is 25% deprotonated at pH 4?

A)3.40
B)3.52
C)4.48
D)4.60

Question 23

At what pH are buffer systems most effective?

A)within 1 pH unit of the pKa value
B)within 2 pH units of the pKa value
C)within 3 pH units of the pKa value
D)within 4 pH units of the pKa value

Question 24

We are preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pKₐ = 4.8)and sodium acetate.Which of the following should the volume of acetic acid be compared to the volume of sodium acetate solution?

A)less than half
B)exactly half
C)equal to
D)about twice

Question 25

Which of the following is the purpose of the physiological mechanism of hyperventilation?

A)to lower [CO₂ (g)] in the blood and increase blood pH
B)to raise [CO₂ (g)] in the blood and increase blood pH
C)to lower [CO₂ (g)] in the blood and decrease blood pH
D)to raise [CO₂ (g)] in the blood and decrease blood pH

Question 26

Hypoventilation is characterized by inability to excrete CO₂ rapidly enough.Which of the following is NOT a cause of hypoventilation?

A)depressant drugs
B)encephalitis
C)narcotics
D)lung diseases

Question 27

The pKₐs of phosphoric acid are 2.1,7.2,and 12.Which of the following ionic form(s)of phosphoric acid is/are present at pH 7.0?

A)HPO4-2
B)H₂PO4-
C)HPO4-2 and PO4-3
D)H₂PO4- and HPO4-2

Question 28

Which of the following characteristics does NOT apply to buffers?

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 2 pKa values.

Question 29

Under which of these conditions does pH = pKₐ?

A)log ([A-]/[HA])= 1
B)[A-] >> [HA]
C)[A-] = [HA]
D)log ([HA]/[A-])= 1

Question 30

Which of the following buffer systems primarily maintain intracellular pH?

A)HPO42-/H₂PO4-;HCO₃-/H₂CO3
B)H3PO4/H₂PO4-;histidine
C)HCO₃-/H₂CO3;H3PO4/H₂PO4-
D)HPO4-/H₂PO4-;histidine

Question 31

Which of the following will occur if an abundance of an organic acid with a pKa of 3.9 is found in the bloodstream?

A)It will be mostly protonated.
B)It will be mostly deprotonated.
C)It will form an effective buffer.
D)It will cause metabolic alkalosis.

Question 32

The enzyme fumarase has a pH optimum of about 7.6.Which of the following would be the buffer of choice to study this enzyme?

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

Question 33

Aspirin contains a carboxylic acid with a pKa of 3.5.Which of the following regarding its structure is correct?

A)It will be mostly protonated in the bloodstream.
B)It will be mostly protonated in the stomach.
C)It will be easily absorbed in the stomach due to its negative charge.
D)It will be easily transported in the bloodstream due to its neutral charge.

Question 34

Water is particularly suited as a solvent for biosystems.Which of the following is NOT a characteristic of water?

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 non-polar substances.
D)Water is relatively chemically inert,yet dissolves a variety of solutes.

Question 35

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)bicarbonate (Ka = 6.3 × 10-11,pKa = 10.24)
C)tris-hydroxymethyl aminomethane (Ka = 8.32 × 10-9,pKa = 8.07)
D)lactic acid (Ka = 1.38 × 10-4,pKa = 3.86)