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)

Accepted Answer

In the acidic environment of the stomach (pH 1.5), only strong acids with pKa values below 1.5 would be predominantly deprotonated. Hydrochloric acid (HCl) has a pKa of -6, which is much lower than the pH of the stomach, so it would be predominantly deprotonated in the stomach. Thus, option E is the best choice.

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

Accepted Answer

Dodecanoic acid has both hydrophilic (carboxylic acid) and hydrophobic (alkyl chain) moieties, which allows it to form micelles in aqueous solutions.

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

Accepted Answer

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

Accepted Answer

The pH of the solution is between the second and third pKa values, which means that two of the carboxylic acid groups are deprotonated and one is still protonated. The pKa value of 4.8 corresponds to the deprotonation of the second carboxylic acid group, so the predominant protonation state is that two carboxylic acid groups are deprotonated and one is still protonated.

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

Accepted Answer

Dissolving of salt crystals involves breaking ionic interactions between positively and negatively charged ions. The other options listed do not involve breaking noncovalent interactions.

Question 6

Which of the following is the conjugate acid of hydrogen phosphate,HPO₄²^-? A)H₂PO₃^- B)H₂PO₄^- C)H₃PO₄ D)H₂PO₄²^- E)none of the above

Accepted Answer

The conjugate acid of hydrogen phosphate will have an additional hydrogen ion (H+) compared to the original molecule. In option B, H₂PO is the conjugate acid of HPO₄²^- because it has gained one hydrogen ion. Option A has lost one proton compared to the original molecule and does not fit the criteria. Option C has lost two proton which is not possible for a conjugate acid. Option D is the molecule itself without any changes. Therefore, option B is the correct answer.

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

Accepted Answer

The answer of Which of the following is the most...

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

Accepted Answer

At pH 9.5, the solution is basic and closer to the pKS value of 9.0 for one of the amine groups than the value of 10.0 for the other amine group. This means that the amine with pKS 9.0 will be deprotonated and neutral (because its pKS is close to the pH of the solution), while the amine with pKS 10.0 will be protonated and positive (because its pKS is farther from the pH of the solution). The carboxylic acid group will also be deprotonated and negative at this pH. Therefore, the correct choice is C.

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

Accepted Answer

To determine the pK_a, we can use the Henderson-Hasselbalch equation: pH = pK_a + log([A-]/[HA]) where [A-] is the concentration of the deprotonated form of the acid, and [HA] is the concentration of the protonated form. We know that at pH 7.0, 24% of the acid is in its deprotonated form, so [A-]/[HA] = 0.24/0.76 = 0.316. Substituting this into the equation and solving for pK_a, we get: 7.0 = pK_a + log(0.316) pK_a = 7.5 Therefore, the answer is B: 7.5.

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

Accepted Answer

Liquid water has a constantly changing structure due to the relatively short duration of individual hydrogen bonds. This results in flickering clusters of hydrogen bonds.

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

Accepted Answer

The answer of Glutamic acid contains two carboxylic acid groups...

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

Accepted Answer

The hydroxyl (-OH) groups present on the glucose molecule act as H-bond acceptors, while the H atoms attached to the O and H atoms of water act as H-bond donors. Each glucose molecule contains multiple -OH groups, allowing it to form H-bonds with as many as 17 water molecules simultaneously. Therefore, option C is correct. Options A, B, and D are incorrect as they provide incorrect information about H-bonding between glucose and water.

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

Accepted Answer

The pK_a value (often referred to as pKa in the context of acids) is a measure of the strength of an acid; the lower the pKa, the stronger the acid. Therefore, the statements given are incorrect based on the pKa values provided. For example, a lower pKa value for lactic acid compared to acetic acid means lactic acid is actually stronger, not weaker. Similarly, the comparisons made in the other options are also based on misunderstandings of how pKa values reflect acid or base strength.

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

Accepted Answer

When the pH of a buffer is below the pKs of the weak acid component, it means the concentration of H+ ions is high, which will shift the equilibrium towards the acidic form of the weak acid. This leads to a higher concentration of acid compared to the base, which results in a ratio of [base]/[acid] less than 1.

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

Accepted Answer

Hydrogen bonding occurs between a hydrogen atom attached to a highly electronegative atom (such as oxygen or nitrogen) and a lone pair of electrons on another electronegative atom. In option C, the hydrogen of an amine (attached to nitrogen) can bond with the oxygen of an alcohol (which has a lone pair of electrons), forming a hydrogen bond. The other options do not have the necessary combination of electronegative atoms and lone pairs for hydrogen bonding to occur.

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

Accepted Answer

The physiological pH range is generally considered to be between 7.35 and 7.45, which falls within the pH range of 5-8.0. Choice D is the only option that includes this range.

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

Accepted Answer

The ratio of base/acid for formic acid can be calculated using the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA]), where pKa is the acid dissociation constant and [A-]/[HA] is the ratio of the conjugate base to the acid.

Substituting the values gives:

7.4 = 3.9 + log([A-]/[HA])

3.5 = log([A-]/[HA])

[A-]/[HA] = 10^(3.5) = 3.16 * 10^3

Therefore, the ratio of base/acid for formic acid in the blood stream at pH 7.4 is 3.16 * 10^3 : 1, or approximately 3,160 : 1.

Option B is the closest value to the calculated ratio.

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

Accepted Answer

Nitric acid is a strong acid not commonly found in biological systems. It is mainly used in industrial settings for the production of fertilizers and explosives. The other acids and bases listed are more commonly found in biochemical settings, with acetic acid being a product of metabolism, ammonia playing a role in protein synthesis, citric acid being a key intermediate in the citric acid cycle, and phosphoric acid being important in cellular energy transfer.

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

Accepted Answer

The answer of A typical amino acid has a carboxylic...

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

Accepted Answer

At pH 7.2, the dominant species of phosphoric acid are HPO4^2- and H2PO4^-. The ratio of these species is given by the Henderson-Hasselbalch equation: ratio = [HPO4^2-]/[H2PO4^-] = 10^(pH-pKa2), where pKa2 = 6.86 for phosphoric acid. Thus, ratio = 10^(7.2-6.86) = 10^0.34 ≈ 2.2.

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

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

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

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

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?

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

Which of the following is the conjugate acid of hydrogen phosphate,HPO₄²^-?

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

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?

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?

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

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?

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

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

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

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

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

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?

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

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?

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?

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

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

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

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

Citric acid is a triprotic acid with three carboxylic acid groups having pKa 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?

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

Which of the following is the conjugate acid of hydrogen phosphate,HPO42-?

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

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

You have been asked to determine the pKa 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 pKa of the acid?