Ch02 - Water: The Solvent for Biochemical Reactions

Question 1

The tendency for an atom to attract electrons to itself in a chemical bond is called

a. polarity.
b. electronegativity.
c. hydrophilicity
d. electrophilicity.

Answer 1

b. electronegativity.

Question 2

If atoms with greatly differing electronegativities form a bond, that bond will be

a. polar.
b. nonpolar.
c. amphipathic.
d. acidic.

Answer 2

a. polar

Question 3

Many of the properties of water can be accounted for by the fact that

a. it is polar
b. it forms hydrogen bonds
c. it is a bent molecule
d. all of these are true

Answer 3

d. all of these are true

Question 4

Which of the following is true about ionic compounds?

a. They are more likely to dissolve in non-polar solvents than covalent compounds
b. They always dissolve completely in water.
c. They never dissolve in polar solvents.
d. Some of them dissolve completely in water or other polar solvents, while others do not.

Answer 4

d. Some of them dissolve completely in water or other polar solvents, while others do not.

Question 5

Which of the following is a correct listing of electronegativity values, from low to high?

a. C, H, O, N
b. N, H, O, C
c. H, C, N, O
d. H, C, O, N

Answer 5

c. H, C, N, O

Question 6

Which of the following elements has the highest electronegativity?

a. C
b. H
c. N
d. O
e. P

Answer 6

d. O

Question 7

The water molecule is polar because:

a. Electrons are not distributed symmetrically in the molecule.
b. The hydrogen atoms are found on one “side” of the molecule.
c. Hydrogen is less electronegative than oxygen.
d. The hydrogen atoms are found on one “side” of the molecule and hydrogen is less electronegative than
oxygen.
e. All of these are correct.

Answer 7

e. All of these are correct.

Question 8

Which of the following molecules is polar?

a. CCl4
b. CH4
c. CO2
d. NH3
e. None of these molecules is polar.

Answer 8

d. NH3

Question 9

Which of the following molecules is amphipathic?

a. sodium chloride
b. acetic acid
c. benzene
d. palmitic acid

Answer 9

d. palmitic acid

Question 10

Which of the following classes of compounds is hydrophilic?

a. Sugars
b. Fatty acids
c. Amino acids
d. Sugars and amino acids.
e. All of these

Answer 10

d. Sugars and amino acids.

Question 11

Which of the following classes of compounds is hydrophobic?

a. Table Salt
b. Cholesterol
c. Phosphate esters
d. Cholesterol and phosphate esters.
e. All of these are hydrophobic.

Answer 11

b. Cholesterol

Question 12

Which of the following molecules has polar bonds but is itself not polar?

a. NH3
b. CO2
c. CH4
d. H2O

Answer 12

b. CO2

Question 13

When a carboxylate side-chain of one amino acid in a protein is in close proximity to a charged amino group of another amino acid, we call the resulting interaction a(n)

a. ion - dipole bond
b. ionic bond
c. van der Waal’s bond
d. salt bridge

Answer 13

d. salt bridge

Question 14

A London dispersion force is another name for a(n)

a. induced dipole - induced dipole bond
b. ionic bond
c. covalent bond
d. non-polar bond

Answer 14

a. induced dipole - induced dipole bond

Question 15

Ionic compounds and polar covalent compounds tend to dissolve in water because of

a. ion-dipole and dipole-dipole interactions
b. dipole-induced dipole interactions
c. van der Waals bonds
d. hydrophobic interactions

Answer 15

a. ion-dipole and dipole-dipole interactions

Question 16

Which of the following is not considered a van der Waal’s force?

a. dipole - dipole bond
b. dipole - induced dipole bond
c. induced dipole - induced dipole bond
d. ion - dipole bond

Answer 16

d. ion - dipole bond

Question 17

A micelle is a structure which

a. aggregates with other micelles in water.
b. has its polar groups on the outside and non-polar groups on the inside when in water.
c. explains how soaps and detergents work.
d. has its polar groups on the outside and non-polar groups on the inside when in water and explains how soaps and detergents work.
e. All of these are true.

Answer 17

d. has its polar groups on the outside and non-polar groups on the inside when in water and explains how soaps and detergents work.

Question 18

Which of the following compounds is most likely to form a micelle?

a. Acetic acid.
b. Glucose.
c. Glycerol.
d. Sodium palmitate.
e. Sodium phosphate.

Answer 18

d. Sodium palmitate.

Question 19

The substance most likely to form a micelle is

a. acetic acid
b. sodium palmitate
c. methyl alcohol
d. acetone

Answer 19

b. sodium palmitate

Question 20

Molecules which contain both hydrophilic and hydrophobic regions are:

a. Amphipathic
b. Amphiphilic
c. Able to form micelles
d. Both amphipathic and amphiphilic
e. All of these

Answer 20

e. All of these

Question 21

How do hydrogen bonds tend to affect the melting and boiling points of substances?

a. They tend to increase both melting and boiling points.
b. They tend to decrease both melting and boiling points.
c. They tend to increase melting points and decrease boiling points.
d. They tend to decrease melting points and increase boiling points.
e. They do not have any affect on either melting or boiling points.

Answer 21

a. They tend to increase both melting and boiling points.

Question 22

Hydrogen bonds

a. play an important role in the solvent properties of water
b. are not involved in protein structure
c. play a role in the properties of DNA, but not of RNA
d. give water a lower boiling point than expected

Answer 22

a. play an important role in the solvent properties of water

Question 23

Which of the following molecules will not form hydrogen bonds?

a. CH4
b. NH3
c. H2O
d. HF

Answer 23

a. CH4

Question 24

How does the strength of hydrogen bonds compare with covalent bonds?

a. Hydrogen bonds are much stronger than covalent bonds.
b. Hydrogen bonds are much weaker than covalent bonds.
c. Hydrogen bonds and covalent bonds have similar strengths.
d. The question cannot be answered without knowing which covalent bonds are being referred to

Answer 24

b. Hydrogen bonds are much weaker than covalent bonds.

Question 25

A hydrogen bond is a special type of

a. dipole - dipole bond
b. induced dipole - induced dipole bond
c. covalent bond
d. ionic bond

Answer 25

a. dipole - dipole bond

Question 26

Which of the following is true regarding hydrogen bonds.

a. They can only form between two different molecules
b. They are important in protein folding but not DNA structure
c. They are important in DNA structure but not protein folding
d. They can be found within a single molecule

Answer 26

d. They can be found within a single molecule

Question 27

In a hydrogen bond

a. three atoms lie in a straight line
b. there is stronger bonding than in a covalent bond
c. unpaired electrons play no role
d. none of the above

Answer 27

a. three atoms lie in a straight line

Question 28

The non-covalent interaction below associated with the strongest force in aqueous solution is

a. dipole-induced dipole
b. hydrophobic interactions
c. hydrogen bonding
d. van der Waals forces

Answer 28

c. hydrogen bonding

Question 29

Which of the following statements about hydrogen bonds is false?

a. The donor is a hydrogen atom bonded to a less electronegative atom then hydrogen.
b. The more linear the bond, the stronger the attraction.
c. The acceptor must contain a non-bonded pair of electrons.
d. It is a type of non-covalent bond.

Answer 29

a. The donor is a hydrogen atom bonded to a less electronegative atom then hydrogen.

Question 30

True hydrogen bonds can NOT form between hydrogen and this element:

a. N
b. F
c. C
d. O
e. All of these elements can form hydrogen bonds.

Answer 30

c. C

Question 31

What is the maximum number of hydrogen bonds a single water molecule can form?

a. 1
b. 2
c. 3
d. 4
e. 5

Answer 31

d. 4

Question 32

Which of the following characteristics makes for a good hydrogen bond acceptor?

a. a high electronegativity
b. a nonbonding pair of electrons
c. both of these
d. neither of these

Answer 32

c. both of these

Question 33

Which of the following characteristics makes for a good hydrogen bond donor?

a. a high electronegativity
b. a nonbonding pair of electrons
c. both of the above
d. neither of the above

Answer 33

a. a high electronegativity

Question 34

Which of the following properties of water are related to its ability to form hydrogen bonds?

a. boiling point
b. melting point
c. density
d. solvent potency
e. all of the choices

Answer 34

e. all of the choices

Question 35

Hydrogen bonds explain which of the following properties of water?

a. Water is a great solvent for all ionic and polar molecules.
b. Water has high melting and boiling points for its small size.
c. Ice expands when frozen.
d. Both the abnormal melting and freezing points and that ice expands when frozen.
e. Hydrogen bonds explain all of these properties.

Answer 35

e. Hydrogen bonds explain all of these properties.

Question 36

Hydrogen bonds can only form when the hydrogen atom is involved in a polar bond.

a. True
b. False

Answer 36

a. True

Question 37

Which of the following is a true statement?

a. most substances contract when they freeze.
b. water expands when it freezes.
c. hydrogen bonding is related to water’s tendency to expand as it freezes.
d. all of these are true

Answer 37

d. all of these are true

Question 38

Refer to Exhibit 2A. Which of the functional groups cannot function as a hydrogen donor to water?

a. I
b. II
c. III
d. IV
e. All can donate a hydrogen to water

Answer 38

b. II

Question 39

Refer to Exhibit 2A. Which of the functional groups is the most electrophilic?

a. I
b. II
c. III
d. IV
e. The answer cannot be determined without further information.

Answer 39

c. III

Question 40

Refer to Exhibit 2A. Which of the groups could not act as a proton acceptor in a hydrogen bond?

a. I
b. II
c. III
d. IV
e. All can accept a hydrogen in a hydrogen bond.

Answer 40

e. All can accept a hydrogen in a hydrogen bond.

Question 41

Is water an acid or a base?

a. Water is an acid.
b. Water is a base.
c. Water is both an acid and a base.
d. Water is neither an acid nor a base.

Answer 41

c. Water is both an acid and a base.

Question 42

2. For an acid that undergoes this reaction:
   HA ↔ H+ + A−
   Ka =?

a. [H+] [A−] / [HA]
b. [H+] [HA] / [A−]
c. [HA] [A−] / [H+]
d. [A−] / [HA] [H+]
e. [H+] / [HA] [A−]

Answer 42

a. [H+] [A−] / [HA]

Question 43

Which will dissociate most in water, a weak acid or a strong acid?

a. A weak acid.
b. A strong acid
c. They should dissociate about the same.
d. It’s impossible to predict.

Answer 43

b. A strong acid

Question 44

Bases are

a. proton donors.
b. proton acceptors.
c. hydrogen bond donors.
d. hydrogen bond acceptors.

Answer 44

b. proton acceptors.

Question 45

Which has the greater Ka, a weak acid or a strong acid?

a. A weak acid.
b. A strong acid
c. They should dissociate about the same.
d. It’s impossible to predict.

Answer 45

b. A strong acid

Question 46

Which has the greater pKa, a weak acid or a strong acid?

a. A weak acid.
b. A strong acid
c. They should dissociate about the same.
d. It’s impossible to predict.

Answer 46

a. A weak acid.

Question 47

The dissociation constant for an acid with a pKa value of 6.0 is

a. 1 × 10^−6
b. −1 × 10^6
c. 1 × 10^6
d. −1 × 10^−6

Answer 47

a. 1 × 10^−6

Question 48

A buffer solution at pH 10 has a ratio of [HA]/[A−] of 10. What is the pKa of the acid?

a. 8
b. 9
c. 10
d. 11
e. 12

Answer 48

d. 11

Question 49

The dissociation constant for an acid is 1 × 10^−6. What is its pKa?

a. −6
b. 6
c. 0.6
d. −0.6

Answer 49

b. 6

Question 50

The pH of a solution of 0.04 M HCl is:

a. 4
b. 1.4
c. 0.4
d. 0.04
e. The pH cannot be determined

Answer 50

b. 1.4

Question 51

The pOH a solution of 0.04 M HCl is:

a. 1.4
b. 10
c. 12.6
d. 13.6
e. The pOH cannot be determined

Answer 51

c. 12.6

Question 52

An HCl solution has a pH = 3. If you dilute 10 mL of the solution to 1000mL, the final pH will be:

a. 1.0
b. 2.0
c. The pH does not change.
d. 4.0
e. 5.0

Answer 52

e. 5.0

Question 53

If a solution has a pH = 9.6, the [H+] is

a. 2.5 × 10^10
b. 9.6 M
c. 2.5 M
d. 2.5 × 10^−10 M
e. 9.6 × 10^−10 M

Answer 53

d. 2.5 × 10^−10 M

Question 54

What is the pH of a solution with [H+] = 10 mM?

a. 10
b. 1
c. 2
d. −2

Answer 54

c. 2

Question 55

Calculate the final pH of a solution made by the addition of 10 mL of a 0.5 M NaOH solution to 500 mL of a 0.4 M HA originally at pH = 5.0 (pKa = 5.0) Neglect the volume change.

a. 6.10
b. 5.09
c. 7.00
d. 5.55

Answer 55

d. 5.55

Question 56

If a solution has a pH = 6, the [H+] is

a. 6 M
b. 10^6 M
c. 10^−6 M
d. 0.6 M

Answer 56

c. 10^−6 M

Question 57

What is the pH of an acetic acid solution where the concentration of acetic acid is 2 mM and the concentration of sodium acetate is 20 mM. The pKa of acetic acid is 4.76.

a. 5.76
b. 10.6
c. 12.6
d. 8.8

Answer 57

a. 5.76

Question 58

The ion product constant for water (Kw) is equal to:

a. 10^14
b. 10^7
c. 10^0
d. 10^−7
e. 10^−14

Answer 58

e. 10^−14

Question 59

In a titration of a weak acid by a strong base

a. two equivalents of base are always needed to neutralize all the acid present
b. the equivalence point cannot be defined exactly
c. there is a region in which the pH changes slowly
d. the equivalence point depends on the nature of the added base

Answer 59

c. there is a region in which the pH changes slowly

Question 60

A solution at pH 7 contains a weak acid, HA. The pKa of the acid is 6.5. What is the ratio of [A−]:[HA]?

a. 1:3
b. 1:1
c. 3:1
d. 10:1

Answer 60

c. 3:1

Question 61

When does a weak acid buffer best?

a. From one pH unit below its pKa to its pKa.
b. From its pKa to one pH unit above its pKa.
c. Within one pH unit of its pKa, both above and below.
d. Weak acids do not make good buffers at all.

Answer 61

c. Within one pH unit of its pKa, both above and below.

Question 62

The inflection point of the titration curve for a weak monoprotic acid is equal to its pKa

a. True
b. False

Answer 62

a. True

Question 63

Which of the following is true?

a. The pH of a solution where the A− to HA ratio is 1 has a pH = pKa.
b. If the pH does not equal the pKa, the solution is not a buffer.
c. The best buffer for any experiment will always have a pH equal to the pKa.
d. If a buffer has more weak acid than conjugate base, the pH will be higher than the pKa.

Answer 63

a. The pH of a solution where the A− to HA ratio is 1 has a pH = pKa.

Question 64

Using the Henderson-Hasselbalch equation, calculate the pH of an ammonia buffer when the NH3:NH4+ ratio is 0.4 moles:0.6 moles. (pK = 9.75)

a. 7.40
b. 9.07
c. 9.25
d. 9.43
e. 11.05

Answer 64

b. 9.07

**9.57

Question 65

An ammonia buffer contains NH3:NH4+ in a ratio of 0.4 moles:0.6 moles (pK = 9.75). What will be the pH if you add 0.01 moles of HCl to this buffer?

a. 8.98
b. 9.04
c. 9.25
d. 9.46
e. 9.52

Answer 65

a. 8.98

Question 66

The ratio of a weak acid and its conjugate base at the point of maximum buffering capacity is

a. 1/1
b. 1/10
c. 10/1
d. no definite ratio is needed

Answer 66

a. 1/1

Question 67

Which substance would be the best buffer at pH 8 if it had to be able to buffer against either acid or base?

a. one with a pKa of 7
b. one with a pKa of 8
c. one with a pKa of 9
d. The pKa of a substance doesn’t tell you whether it would be a good buffer at this pH.

Answer 67

b. one with a pKa of 8

Question 68

Buffering capacity refers to

a. the effectiveness of commercial antacids
b. the extent to which a buffer solution can counteract the effect of added acid or base
c. the pH of a buffer solution
d. the molecular weight of the substance used as a buffer

Answer 68

b. the extent to which a buffer solution can counteract the effect of added acid or base

Question 69

If the pH of 1 liter of a 1.0 M carbonate buffer is 7.0, what is the molar ratio of H2CO3 to HCO3−? (pK = 6.37)

a. 0.234
b. 4.27
c. 6.37
d. 7.00
e. 10.20

Answer 69

b. 4.27

Question 70

Consider a reaction that produces a significant amount of hydrogen ion and is to be carried out a pH 7. Only two acids are available for making the buffer solution. The pKa values for acids A and B are 6.3 and 7.3, respectively. Which acid would serve as the optimum buffer for this reaction? Or would carrying out the reaction in water simply serve as well?

a. acid A
b. acid B
c. water
d. both acids would be equally effective

Answer 70

a. acid A

Question 71

Which of the following acids would serve as a good buffer for a reaction at pH = 8.0?

I. acetic acid | Ka = 1.76 × 10^−5
II. H2PO4− | Ka = 6.31 × 10^−8
III. bicarbonate | Ka = 5.6 × 10^−11
IV. TRIS | Ka = 5.01 × 10^−9

a. I
b. II
c. III
d. IV

Answer 71

d. IV

Question 72

If the pH of 1 liter of a 1.0 M carbonate buffer is 7.0, what is actual number of moles of H2CO3 and HCO3−? (pK = 6.37)

I. moles of H2CO3 = 0.86
moles of HCO3− = 0.14

II. moles of H2CO3 = 0.81
moles of HCO3− = 0.19

III. moles of H2CO3 = 0.76
moles of HCO3− = 0.24

IV. moles of H2CO3 = 0.19
moles of HCO3− = 0.81

V. moles of H2CO3 = 0.14
moles of HCO3− = 0.86

a. I
b. II
c. III
d. IV
e. V

Answer 72

d. IV

Question 73

A buffer solution

a. is used to control the pH of a solution
b. contains at least 100 times more of a weak acid than its conjugate base
c. contains at least 100 times less of a weak acid than its conjugate base
d. always has a pH of 7

Answer 73

a. is used to control the pH of a solution

Question 74

The main intracellular buffer system is

a. H3PO4/H2PO4−
b. H2PO4−/ HPO4^2−
c. HPO4^2−/PO4^3−
d. H3PO4/PO4^3−

Answer 74

b. H2PO4−/ HPO4^2−

Question 75

Refer to Exhibit 2B. The enzyme lysozyme has an optimum pH close to 5. A suitable buffer would be:

a. Acetate
b. Carbonate
c. Phosphate
d. Pyruvate

Answer 75

a. Acetate

Question 76

Refer to Exhibit 2B. An ammonium buffer would work well at this pH:

a. 5.6
b. 7.0
c. 9.0
d. 11.0
e. None of these

Answer 76

c. 9.0

Question 77

Refer to Exhibit 2B. A carbonate buffer would work well at this pH:

a. 4.0
b. 6.0
c. 8.0
d. 10.0
e. 6.0 and 10.0

Answer 77

e. 6.0 and 10.0

Question 78

Refer to Exhibit 2B. A phosphate buffer would work well at this pH:

a. 5.0
b. 7.0
c. 8.0
d. 10.0
e. 7.0 and 8.0

Answer 78

e. 7.0 and 8.0

Question 79

Refer to Exhibit 2B. Which of the following would make the best buffer at pH =10.0?

a. Acetic acid and sodium acetate
b. Tris and its acid form
c. H2CO3 and NaHCO3
d. Na2HPO4 and NaH2PO4
e. NaHCO3 and Na2CO3

Answer 79

e. NaHCO3 and Na2CO3

Question 80

Which of the following is important to know when deciding if a given buffer will be effective for an experiment?

a. the pKa of the buffer compound
b. the buffer capacity
c. the concentration of the buffer
d. whether the experiment is likely to generate hydrogen ions or hydroxide ions
e. all of these are important considerations

Answer 80

e. all of these are important considerations

Question 81

Non physiological buffers such as HEPES and PIPES have come into common use because

a. they are inexpensive
b. they can be prepared much more easily than other buffers
c. they have less tendency to interfere with reactions
d. they contain nitrogen

Answer 81

c. they have less tendency to interfere with reactions

Question 82

Buffers which lack biological activity and are unlikely to interfere with any biochemical reactions include:

a. Tris.
b. Hepes.
c. Phosphate.
d. Both Tris and HEPES.
e. All of these.

Answer 82

d. Both Tris and HEPES.

Question 83

Which of the following is not true?

a. A buffer is a solution which maintains a solution at a neutral pH
b. Buffer solutions are made to resist change in pH
c. Zwitterion buffers are less likely to interfere with biological reactions than non-zwitterions
d. HEPES is a zwitterion buffer

Answer 83

a. A buffer is a solution which maintains a solution at a neutral pH

Question 84

The main blood buffer system is

a. H2CO3/HCO3−
b. HCO3−/CO3^2−
c. H2CO3/CO3^2−
d. none of the above

Answer 84

a. H2CO3/HCO3−

Question 85

Buffers work to maintain pH because

a. they obey LeChatlier’s principle
b. weak acids cannot change the pH of a solution
c. weak bases added to strong bases neutralize each other
d. they destroy the hydrogen ion that is added

Answer 85

a. they obey LeChatlier’s principle

Question 86

Explain why carbon dioxide is nonpolar.

Answer 86

A carbon dioxide molecule has two C=O polar bonds. However, the bonds in the molecule may be polar, but the molecule itself can be nonpolar because of its geometry. The CO2 molecule is linear; therefore, the attraction of the oxygen for the electrons in one bond is cancelled out by the equal and opposite attraction for the electrons by the oxygen on the other side of the molecule, resulting in a nonpolar molecule

Question 87

Which of the following statements is true of dipole-induced dipole interactions?

a. They occur between molecules that are dipoles, with the partial positive side of one molecule attracting the partial negative side of another molecule.
b. They involve a permanent dipole inducing a transient dipole in a nonpolar molecule.
c. They are the attraction between two molecules, lacking dipoles, bumping into each other and distorting each other’s electron cloud.
d. They give rise to a London dispersion force between transient-induced dipoles

Answer 87

b. They involve a permanent dipole inducing a transient dipole in a nonpolar molecule.

Question 88

Distinguish between the hydrogen bonding found in liquid water and ice

Answer 88

In liquid water, hydrogen bonds are constantly breaking and new ones are constantly forming, with some molecules breaking off and others joining the cluster. An ice crystal, in contrast, has a more or less stable arrangement of hydrogen bonds and its number of molecules is many orders of magnitude greater than 100.

Question 89

Which of the following equations represents the relationship between the pKa of an acid and the pH of a solution containing the acid and its conjugate base?

a. Arrhenius equation
b. Henderson–Hasselbalch equation
c. Nernst equation
d. Butler–Volmer equation

Answer 89

b. Henderson–Hasselbalch equation

Question 90

Which of the following principles states that if stress is applied to a system in equilibrium, the equilibrium will shift in the direction that relieves the stress?

a. Pauli exclusion principle
b. Mach’s principle
c. Fermat’s principle
d. Le Chatelier’s principle

Answer 90

d. Le Chatelier’s principle