Deck 2: Water

Question 1

Molecules that are both hydrophobic and hydrophilic are .

A) amphipathic
B) amphoteric
C) bipolar
D) not possible

Answer 1

amphipathic

Question 2

Oil and water do not form a solution due to .

A) the hydrophobic effect
B) the inability of oil to hydrogen bond with water
C) the nonpolarity of oil
D) All of the above (A-C)
E) A and C only

Answer 2

All of the above (A-C)

Question 3

The osmotic pressure of a 0.010 M sucrose C₁₂H₂₂O₁₁) solution at 25 °C is 0.24 atm. How does the osmotic pressure of a 0.010 M glucose C₆H₁₂O₆) solution at 25 °C compare to this? Note that neither solute is volatile or ionizable.

A) The glucose solution has a lower osmotic pressure because its molar mass is lower than sucrose.
B) The glucose solution has a higher osmotic pressure because its molar mass is lower than sucrose.
C) The osmotic pressures are equal because the solutions have the same molar concentration.
D) Nothing can be said about the osmotic pressure of the glucose solution without more information.

Answer 3

The osmotic pressures are equal because the solutions have the same molar concentration.

Question 4

What is the difference between a particle being hydrated versus being solvated?

A) A hydrated particle is surrounded by a shell of water. A solvated molecule is surrounded by a shell of solvent molecules, not necessarily water.
B) The terms hydrated and solvated mean exactly the same thing.
C) A hydrated particle has reacted with hydrogen. A solvated particle is dissolved in a solvent.
D) The word hydrated is used only when the solute is an electrolyte.

Question 5

Some ions such as thiocyanate that are poorly solvated in water and can enhance the solubility of nonpolar compounds in water by disordering the water molecules are called .

A) azeotropes
B) hydrophobic ions
C) zeolytes
D) chaotropes

Question 6

Which would you expect to be most soluble in water?

A) I
B) II
C) III
D) IV

Question 7

The pressure is the pressure required to prevent the flow of solvent through a solvent-permeable membrane that separates two solutions of different solute concentration.

A) hydrostatic
B) electromotive
C) osmotic
D) partial

Question 8

The abundance of water in the cells and tissues helps to minimize temperature fluctuations. This is due to what property of water?

A) density
B) viscosity
C) specific heat
D) boiling point

Question 9

What is the maximum number of hydrogen bonds that one water molecule can have with neighboring water molecules?

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

Question 10

Which is not a proper way to form a hydrogen bond? The symbol ʺRʺ represents a general organic group. The hydrogen bonding is represented by dashed lines.)

A) I
B) II
C) III
D) IV

Question 11

Which substance do you expect to be most soluble in water?

A) ammonia, NH₃
B) methane, CH₄
C) carbon dioxide, CO₂
D) nitrogen, N₂

Question 12

Which statement does not explain the polarity of water?

A) Oxygen is more electronegative than hydrogen.
B) Water molecules have a bent geometry (V-shaped).
C) The oxygen in water has (sp² hybrid orbitals.
D) In water the hydrogen carries a partial positive charge (δ⁺).

Question 13

Which statement explains the cleaning action of soap on greasy dishes?

A) The soap changes the water-solubility of the grease so that it is easily dissolved by the water.
B) The grease is trapped inside the hydrophobic interior of micelles made of soap molecules.
C) The soap chemically breaks down the grease into smaller, more water-soluble molecules.
D) The soap hydrates the grease with its polar head groups and holds it in suspension.

Question 14

Compounds that ionize when dissolved in water are called .

A) electrolytes
B) polar compounds
C) hydrophobic compounds
D) amphipathic compounds

Question 15

The osmotic pressure of an aqueous solution depends on

A) the chemical nature of the solute.
B) the molar concentration of solute.
C) the hydrophobic effect of the solute.
D) All of the above.
E) None of the above.

Question 16

Which molecule or ion below is amphipathic?

A) H₂NCH₂COOH glycine
B) H₂O
C)(CH₃CH₂)₁₄COO^-
D) CH₃CH₂CH₂CH₂CH₃

Question 17

Solutes diffuse more slowly in cytoplasm than in water because of

A) the higher viscosity of water.
B) the higher heat of vaporization of water.
C) the presence of many crowded molecules in the cytoplasm.
D) the absence of charged molecules inside cells.

Question 18

Electrolytes dissolve readily in water because

A) they are held together by electrostatic forces.
B) they are hydrophobic.
C) water molecules can cluster about cations.
D) water molecules can cluster about anions.
E) water molecules can cluster about cations and anions.

Question 19

A molecule or ion is said to be hydrated when it .

A) is neutralized by water
B) is surrounded by water molecules
C) reacts and forms a covalent bond to water
D) aggregates with other molecules or ions to form a micelle in water

Question 20

Which is true about the solubility of electrolytes in water?

A) They are all insoluble in water.
B) They are usually only sparingly soluble in water.
C) They often form super-saturated aqueous solutions.
D) They readily dissolve and ionize in water.

Question 21

The three dimensional structure of most proteins is largely determined by

A) other proteins which fold them.
B) weak noncovalent interactions.
C) denaturation.
D) hydrogen bonds.
E) All of the above

Question 22

The self-ionization of water is .

A) a unimolecular dissociation of a single water molecule to H⁺ and OH^-
B) a biomolecular reaction between two water molecules to yield H₃O⁺ and OH^-
C) a result of hydrophobic interactions
D) a termolecular reaction involving the simultaneous collision of H₂O, H⁺ and OH^-

Question 23

Water is a nucleophile, yet it does not usually hydrolyze macromolecules in cells because

A) covalent bonds linking macromolecule subunits are stable at cell pH.
B) covalent bonds linking macromolecule subunits are stable at cell temperature.
C) the concentration of water is much too small in cells.
D) A and B

Question 24

How does the ion-product of water, K_w, relate to the equilibrium constant, K_eq, for the dissociation reaction of water?

A) K_w is found by multiplying K_eq by the concentration of water.
B) K_w just another symbol for K_eq , so they are equal.
C) K_w is found by dividing K_eq by the ideal gas constant.
D) K_w is found by multiplying K_eq by the concentrations of hydronium ion and hydroxide ion.

Question 25

The oxygen atom of water is nucleophilic because

A) it has a negative oxidation number.
B) it carries a partial positive charge.
C) it has two unshared pair of electrons.
D) it seeks electron-rich molecules.
E) All of the above

Question 26

Which of these noncovalent forces in biological systems is usually the strongest?

A) hydrogen bonds
B) London dispersion forces
C) hydrophobic interactions
D) van der Waals forces

Question 27

Pure water has a concentration of

A) 18 g/ml.
B) 1 g/ml.
C) 1000 g/ml.
D) 55 M.

Question 28

Which statement below is true about the relative lifetime of a hydrogen bond, compared to the rate of waterʹs ionization to hydroxide ions and hydronium ions?

A) The strength of hydrogen bonding makes its dissociation much slower than the ionization of water.
B) The rate of dissociation of a hydrogen bond is the same order of magnitude as the rate of ionization of water.
C) The two rates are linked in such a way that the more the water is ionized, the stronger and longer lasting hydrogen bonding will be.
D) The lifetime of a water molecule before it is ionized is about 10⁹ greater than the lifetime of a hydrogen bond.

Question 29

Hydrogen bonds can occur when hydrogen is covalently bonded to atoms like nitrogen and oxygen. What property of nitrogen and oxygen is important for this?

A) atomic mass
B) ionizability
C) hydrophobicity
D) electronegativity

Question 30

Which of the following is NOT a ʺweakʺ interaction?

A) hydrogen bonds
B) van der Waals forces
C) disulfide bonds
D) ionic interactions
E) hydrophobic interactions

Question 31

The ion-product constant for water, K_w, is

A) 1 x 10^-7 M².
B) 1 x 10^-7 M.
C) 1 x 10^-14 M².
D) 1 x 10^-14 M.

Question 32

Which is true about hydrogen bonding for biological molecules?

A) Hydrogen bonds are strong enough to confer structural stability, for example in DNA.
B) Hydrogen bonds are weak enough to be easily broken weaker than covalent bonds).
C) They contribute to the water solubility of many macromolecules.
D) All of the above

Question 33

London dispersion forces are attractive forces that arise due to

A) infinitesimal dipoles generated by the constant random motion of electrons.
B) permanent dipoles of molecules containing covalent bonds between atoms of very different electronegativities.
C) the hydrophobic effect.
D) ion pairing between oppositely charged functional groups.

Question 34

In pure water hydronium ions are formed by attack of oxygen on a proton in an adjacent water molecule.

A) ionic
B) nucleophilic
C) electrophilic
D) covalent

Question 35

The aggregation of nonpolar molecules or groups in water is thermodynamically due to the

A) increased entropy of the nonpolar molecules when they associate.
B) decreased enthalpy of the system.
C) increased entropy of the water molecules.
D) very strong van der Waals forces among the nonpolar molecules or groups.

Question 36

Enzymes which condense subunits of macromolecules during their synthesis usually

A) transfer an acyl or carbonyl group to an electrophile.
B) exclude water from the active site.
C) contain inhibitors of hydrolases.
D) are catalyzing thermodynamically favored reactions.
E) All of the above

Question 37

Which of the following weak interactions is not an electrostatic interaction?

A) hydrogen bonds
B) charge-charge interactions
C) hydrophobic interactions
D) van der Waals forces

Question 38

Attractions of oppositely charged functional groups of proteins are sometimes called .

A) salt bridges or ion pairing
B) disulfide bridges
C) London bridges
D) hydrophilic bridges

Question 39

Which statement best characterizes the distribution of charge in the hydronium ion, H₃O⁺?

A) The positive charge is distributed over all of the atoms in the ion.
B) The positive charge is localized only on the oxygen atom.
C) The positive charge is distributed between the three hydrogen atoms only.
D) The positive charge is localized on only one of the hydrogen atoms.

Question 40

Water clustered about nonpolar molecules contribute to hydrophobic interactions because

A) Their number is minimized to increase the total entropy of water.
B) Nonpolar molecules are more highly organized than polar molecules.
C) Water molecules in the cell are more organized in the regions away from the nonpolar molecule.
D) All of the above
E) B and C

Question 41

The water solubility of alcohols with a single hydroxyl group increases as a function of molecular weight.

Question 42

For a weak acid with a pK_a = 6.5, the effective buffering range is usually considered to be

A) pH 6 to pH 7.
B) pH 6.4 to pH 6.6.
C) pH 5.5 to pH 7.5.
D) dependent on the molarity of the acid.
E) B and C

Question 43

The pH of a 10^-4 M solution of HCl is

A) 3.
B) 3.5.
C) 4.
D) 4.5.
E) greater than 4.5.

Question 44

Basic solutions form when chemicals are dissolved in water and remove

A) OH^-.
B) H⁺.
C) Na⁺.
D) A and B
E) A, B and C

Question 45

pK_a values of phosphoric acid are 2.2, 7.2 and 12.7. A phosphate buffer of pH = 7.4 can be prepared using

A) H₂PO₄^- and HPO₄^2-.
B) HPO₄^2- and PO₄^3-.
C) H₃PO₄ and HCl.
D) None of the above

Question 46

Histidine contains an imidazole group which is titratable. A histidine buffer can be prepared using

A) NaOH and histidine.
B) NaOH and imidazolium ion.
C) imidazolium ion and imidazole conjugate base).
D) HCl and imidazole.
E) All of the above

Question 47

Blood pH is primarily regulated by

A) a protein buffer system.
B) the carbon dioxide - carbonic acid - bicarbonate buffer system.
C) the phosphate buffering system.
D) carbonic acid (H₂CO₃).
E) B and C

Question 48

Intracellular buffers include

A) proteins.
B) inorganic phosphate.
C) hemoglobin.
D) Both A and B
E) A, B and C

Question 49

Compare solution A with pH = 4 to solution B with pH = 6.

A) The concentration of hydronium ion in solution A is twice that in solution B.
B) Solution A has greater buffering capacity than solution B.
C) The concentration of hydronium ion in solution A is 100 times that in solution B.
D) The hydroxide concentrations are equal in the two solutions since pH only measures the concentration of H⁺.

Question 50

The ratio of the concentration of a over describes the proportions of forms of a weak acid necessary to satisfy the Henderson-Hasselbalch equation.

A) conjugate acid; conjugate base
B) conjugate base; conjugate acid
C) proton donor; proton acceptor
D) proton acceptor; proton donor
E) B and D

Question 51

Acetic acid has a pK_a of 4.8. How many milliliters of 0.2 M acetic acid and 0.1 M sodium acetate are required to prepare 1 liter of 0.1 M buffer solution having a pH of 4.8?

A) 500 ml acetic acid and 500 ml sodium acetate
B) 250 ml acetic acid and 250 ml sodium acetate, then 500 ml water
C) 250 ml acetic acid and 500 ml sodium acetate, then 250 ml water
D) 500 ml acetic acid and 250 ml sodium acetate, then 250 ml water

Question 52

The imidazolium ion has a pK_a = 7.0. Imidazolium buffers can be prepared for pH values of

A) 6.5 to 7.5.
B) 6.1 to 7.1.
C) 5.5 to 8.5.
D) 6.0 to 8.0.
E) 6.0 to 7.5.

Question 53

A solution containing 10^-8 M HCl and 10^-8 M acetic acid contains H⁺ which is supplied mostly by

A) the strong acid.
B) the weak acid.
C) both the strong and the weak acids.
D) water.
E) All of the above

Question 54

The pH of human blood is maintained at 7.4 by

A) buffering proteins.
B) carbon dioxide-carbonic acid buffer systems.
C) a bicarbonate buffer system.
D) B and C
E) A, B and C

Question 55

The Henderson-Hasselbalch equation can be used to calculate

A) the pH of a solution of an organic acid.
B) the amount of salt and acid to add to form a specific buffer.
C) the pK_a of a weak acid.
D) All of the above
E) A and C only

Question 56

If human blood is not maintained at close to pH = 7.4, a person can develop

A) acidosis.
B) alkalosis.
C) diabetes.
D) Both A and B
E) None of the above

Question 57

At the midpoint of a titration curve

A) the concentration of a conjugate base is equal to the concentration of a conjugate acid
B) the pH equals the pK_a
C) the ability of the solution to buffer is best
D) All of the above
E) A and B only

Question 58

Since HCl is a strong acid its value of K_a is .

A) effectively equal to infinity
B) equal to K_w
C) zero
D) dependent on the concentration of HCl

Question 59

The solubility rule ʺlike dissolves likeʺ refers primarily to similarities in amphipathic nature between the solute and solvent.

Question 60

The hydrogen bonding between water molecules in ice gives water an unusually low melting point compared to other molecules of similar size and molecular weight that cannot form hydrogen bonds.

Question 61

An intermediate formed by the enzyme glutamine synthetase, gamma-glutamyl phosphate, is rapidly hydrolyzed by water if the enzyme is not around to protect it.

Question 62

When acid is added to pure water, K_w, the ion-product constant of water, changes.

Question 63

The equilibrium constant of water K_eq) is the rate that dissociation of the molecule occurs at room temperature.

Question 64

Hydrophobic interactions are sometimes called ʺbondsʺ, because each one is as strong as a covalent bond.

Question 65

Synthetic compounds used as buffers are not as valuable for experiments as naturally occurring compounds used as buffers.

Question 66

The buffering capacity of a weak acid and its conjugate base is strongest when the pH = pK_a.

Question 67

Water molecules that surround a less polar molecule in solution are immobile and ordered.

Question 68

Proteins dissolved in water can be hydrolyzed by nucleophilic attack from the water molecules.

Question 69

Since the pK_a of acetic acid is 4.8, it can be used to prepare a buffer to maintain physiological pH.

Question 70

The combined effect of many weak noncovalent interactions can be very significant in determining factors such as three-dimensional structure for large biological molecules.

Question 71

Salt bridges are often found on the surfaces of proteins where they are stabilized by water.

Question 72

The H⁺ or H₃O⁺ in cells is the same concentration as that of undissociated water.

Question 73

A hydrated potassium ion is surrounded by a shell of water molecules oriented primarily with their oxygen atoms toward the potassium ion.

Question 74

Van der Waals forces are very strongly repulsive at short nuclear distances and very weak at long internuclear distances.

Question 75

Hydrogen bonds in the interior of a protein or other macromolecule are stronger than those on the exterior.

Question 76

The attractive force between two atoms is maximized when they are separated by the sum of their van der Waals radii.

Question 77

Micelles are stabilized in water by interactions of nonpolar molecules with each other.

Question 78

Hyperventilation can result in alkalosis because there is excessive loss of carbon dioxide and, therefore a loss of carbonic acid.

Question 79

In the detergent, sodium dodecyl sulfate, the sulfate groups are very hydrophobic.

Question 80

The strength of van der Waals forces between two molecules changes as the distance between them changes.