Deck 2: The Matrix of Life: Weak Interactions in an Aqueous Environment

Question 1

If gastric juice has a pH of about 1.5,which of the following would be predominantly deprotonated in the stomach?

A)phenol (pK_a = 9.9)
B)acetic acid (pK_a = 4.7)
C)lactic acid, (pK_a = 3.9)
D)phosphoric acid (pK_a = 2.1)
E)hydrochloric acid (pK_a = -6)

Answer 1

E

Question 2

Which of the following would likely form micelles in an aqueous solution?

A)hexane
B)glucose
C)glutamic acid
D)dodecanoic acid
E)none of the above

Answer 2

D

Question 3

In the following titration curve,what does the inflection point represent?

A)pH of solution equals pK_a of weak acid
B)concentration of weak acid and conjugate base are equal
C)the pH where the solution would function most effectively as a buffer
D)the weak acid is 50% protonated,50% deprotonated
E)all of the above

Answer 3

E

Question 4

Citric acid is a triprotic acid with three carboxylic acid groups having pK_a values of 3.1,4.8,and 6.4.If a solution of citric acid has a pH of 5.5,what can be said about the predominant protonation state of the citric acid?

A)1 carboxylic acid group is deprotonated,2 are protonated
B)2 carboxylic acid groups are deprotonated,1 is protonated
C)all 3 carboxylic acid groups are deprotonated
D)all 3 carboxylic acid groups are protonated
E)the protonation state cannot be determined

Question 5

Which of the following represents the breaking of a noncovalent interaction?

A)hydrolysis of an ester
B)dissolving of salt crystals
C)ionization of water
D)decomposition of hydrogen peroxide
E)none of the above

Question 6

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

A)H₂PO₃^-
B)H₂PO₄^-
C)H₃PO₄
D)H₂PO₄^2-
E)none of the above

Question 7

Which of the following is the most likely noncovalent interaction observed between a carboxylic acid and an alcohol?

A)charge-charge interaction
B)charge-dipole interaction
C)dipole-dipole interaction
D)dipole-induced dipole interaction
E)formation of an ester bond

Question 8

Lysine contains two amine groups (pK_a values of 9.0 and 10.0)and a carboxylic acid group (pK_a 2.2).In a solution of pH 9.5,which of the following would best describe the protonation and charge state of lysine?

A)carboxylic acid: deprotonated and neutral;both amines: protonated and positive
B)carboxylic acid: deprotonated and negative;both amines: deprotonated and neutral
C)carboxylic acid: deprotonated and negative;amine (pK_a 9.0): deprotonated and neutral;amine (pK_a 10.0): protonated and positive
D)carboxylic acid: deprotonated and negative;amine (pK_a 9.0): protonated and positive;amine (pK_a 10.0): deprotonated and neutral
E)carboxylic acid: deprotonated and neutral;amine (pK_a 9.0): deprotonated and neutral;amine (pK_a 10.0): protonated and positive

Question 9

You have been asked to determine the pK_a of an unknown acid.In a solution at pH 7.0,you find that 24% of the acid is in its deprotonated form.What is the pK_a of the acid?

A)7.9
B)7.5
C)6.5
D)5.6
E)none of the above

Question 10

Which of the following best explains the hydrogen bonding that occurs in water?

A)the average number of H-bonds formed by one water molecule is the same in liquid and solid water,the only difference is the duration of the H-bond
B)the number of H-bonds formed by one water molecule is greater in liquid water than in solid water
C)the structure of liquid water is best described as flickering clusters of H-bonds due to the relative short duration of individual H-bonds
D)each water molecule is capable of forming 8 H-bonds: 2 from each lone pair of electrons and 2 from each hydrogen
E)none of the above

Question 11

Glutamic acid contains two carboxylic acid groups (pK_a values of 2.2 and 4.2)and an amine group (pK_a 9.7).What is the pI for glutamic acid?

A)3.2
B)6.0
C)6.5
D)7.0
E)none of the above

Question 12

Given the structure of a glucose molecule,which of the following explains the hydrogen bonding between glucose and water?

A)H-bonds will form with glucose always being the H-bond donor
B)H-bonds will form with water always being the H-bond donor
C)each glucose molecule could H-bond with as many as 17 water molecules
D)due to the cyclic structure of glucose,H-bonding with water does not occur
E)none of the above

Question 13

Since pK_a = -log K_a,which of the following is a correct statement?

A)acetic acid (pK_a = 4.7)is stronger than lactic acid, (pK_a = 3.9)
B)lactic acid, (pK_a = 3.9)is weaker than all forms of phosphoric acid, (pK_a = 2.1,6.9 and 12.4)
C)since the pK_a for conversion of the ammonium ion to ammonia is 9.25,ammonia is a weaker base then the acetate ion
D)for carbonic acid with pK_a values of 6.3 and 10.3,the bicarbonate ion is a stronger base than the carbonate ion
E)none of the above

Question 14

If a buffer is made with the pH below the pK_a of the weak acid,the ratio of [base]/[acid] will be:

A)less than 1
B)greater than 1
C)equal to 1
D)equal to 0
E)cannot be determined

Question 15

Which of the following atoms could interact through a hydrogen bond?

A)the oxygen of a ketone and the hydrogen of an aldehyde
B)the oxygen of methanol and a hydrogen on the methyl carbon of methanol
C)the hydrogen of an amine and the oxygen of an alcohol
D)the hydrogen on an aromatic ring and the oxygen of carbon dioxide
E)none of the above

Question 16

What pH range is generally considered to be the physiological pH range?

A)1.5-3.0
B)4.5-7.0
C)5.5-9.0
D)6.5-8.0
E)7.5-10.0

Question 17

Formic acid is the active agent in an ant bite.What is the ratio of base/acid for formic acid (pK_a 3.9)in the blood stream at pH 7.4?

A)3.16 $\times$ 10^-4
B)3.16 $\times$ 10³
C)3.5
D)0.54
E)1.90

Question 18

Which of the following acids or bases is least likely to be encountered in a biochemical setting?

A)nitric acid
B)acetic acid
C)ammonia
D)citric acid
E)phosphoric acid

Question 19

A typical amino acid has a carboxylic acid and an amine with pK_a values of 2.3 and 9.6,respectively.In a solution of pH 4.5,which of the following best describes the protonation and charge state of the amino acid?

A)carboxylic acid: protonated and neutral;amine: deprotonated and negative
B)carboxylic acid: protonated and neutral;amine: protonated and neutral
C)carboxylic acid: deprotonated and negative;amine: protonated and neutral
D)carboxylic acid: deprotonated and negative;amine: protonated and positive
E)carboxylic acid: deprotonated and negative;amine: deprotonated and neutral

Question 20

Given the pK_a values for phosphoric acid of 2.14,6.86 and 12.4,what is the ratio of HPO₄^2-/H₂PO₄^- in a typical muscle cell where the pH is 7.2?

A)0.46
B)2.2
C)6.3 $\times$ 10^-6
D)1.1 $\times$ 10⁵
E)none of the above

Question 21

Lactic acid is a common product of actively working muscle.It is transported via the bloodstream to the liver.What percent of lactic acid is ionized in the bloodstream if the pH is 7.40 and the pK_a is 3.86?

Question 22

Use the equilibrium equation of the blood buffer to predict what would happen to blood pH if respiration were to slow significantly.

Question 23

Imidazole is a commonly used buffer in biochemistry labs.With a pK_a of 7.0,what would be the ratio of base to acid at pH 7.4?

Question 24

What happens to DNA when placed into an aqueous solution at physiological pH?

A)individual DNA molecules attract each other due to presence of positive and negative charges
B)individual DNA molecules repel each other due to presence of negative charges
C)individual DNA molecules repel each other due to presence of positive charges
D)DNA molecules bind to negatively charged proteins
E)none of the above