FL 8 - Chem/Phys

Question 1

What is known about an electrochemical half reaction that has a more positive cell potential than the other half reaction?

Answer 1

The half reaction that is more positive is the species that will be reduced, which will always occur at the cathode.

Question 2

During the reduction of a mole of oxygen to water shown in Figure 1, how much charge is transferred?

A. 1 x 10⁵ C

B. 2 x 10⁵ C

C. 4 x 10⁵ C

D. 6 x 10⁸ C

Answer 2

C. 4 x 10⁵ C

First, we need to balance the reaction:

O₂ (g) + 4 H⁺ → 2 H₂O (l)

This reaction is now balanced in terms of atoms, but as a redox reaction, it must also be balanced with regard to charge. We currently have a +4 charge on the left and a 0 charge on the right. To balance, we must add 4 electrons to the left side of the reaction.

O₂ (g) + 4 H⁺ + 4 e^- → 2 H₂O (l)

Now, we can see that 4 moles of electrons are transferred per mole of O₂. Faraday’s constant tells us that approximately 10⁵ coulombs are present per mole of electrons, so:

4 mol e^- x 10⁵ C/mol e^- = 4 x 10⁵ C

Question 3

A magnetic field is measured at point A in Figure 1. Which of the following is true?

A. The induced magnetic field points out of the page.

B. The induced magnetic field points down the page.

C. The induced magnetic field points up the page.

D. The induced magnetic field points into the page.

Answer 3

D. The induced magnetic field points into the page.

Figure 1 shows the microbe-containing electrode in chamber 1, on the left. In paragraph 2, this electrode is described as the source of electrons, which then travel along the wire to chamber 2. In other words, electrons are traveling from left to right, or clockwise. However, remember that current and electrons always flow in opposite directions! Thus, current is moving counterclockwise. Using the right-hand-rule, point your right thumb in the direction of the moving current (to the left), and curl your fingers around the wire. Your fingers should point into the page at point A. The flow of current and the direction of the induced magnetic field are shown below:

Question 4

At pH = 7.3, what is the bond order of the shortest bond to oxygen in glycine?

Answer 4

1.5

Upon looking at the structure of glycine, you might be tempted to think that the shortest bond would be the double bond between the oxygen and the carbon in the carboxyl group of the amino acid. However, at physiological pH, the carboxyl group is deprotonated, and the negative charge is therefore delocalized by resonance between the two oxygen atoms. As a result, the bond order of the shortest bond in glycine is not 2, but rather 1.5:

Question 5

Why is more heat required to convert water to water vapor than is required to convert ice to water?

Answer 5

All hydrogen bonds have to be broken in order to covert water to vapor.

More energy is needed to evaporate water to vapor than to melt ice to water because no hydrogen bonds exist in water vapor. Therefore, all hydrogen bonds need to be broken during evaporation, which requires energy. During melting, however, hydrogen bonds are rearranged but not eliminated. Consequently, more energy is needed for evaporation than melting, as shown in the above figure.

Question 6

During a certain experiment, retinol (shown below) must be isolated by extraction.

In which solvent would one expect retinol to dissolve most readily?

A. Hexane

B. Acetonitrile

C. Water

D. Ethanol

Answer 6

A. Hexane

Figure 1 shows the structure of retinol, which is a large organic molecule. Though it has an alcohol group that is polar, the vast majority of the molecule is nonpolar. Therefore, it would be most soluble in a nonpolar (hydrophobic) solvent. Of the choices listed, hexane is the most nonpolar, so choice A is correct.

Question 7

In the context of plasma membranes, unsaturated fatty acids tend to make the membrane (more/less) fluid.

Answer 7

In the context of plasma membranes, unsaturated fatty acids tend to make the membrane more fluid.

Question 8

In multi-step reactions, the step with the _______ rate determines the overall rate of the reaction, so it is known as the rate-limiting step.

Answer 8

In multi-step reactions, the step with the slowest rate determines the overall rate of the reaction, so it is known as the rate-limiting step.

This will also be the step that has the highest activation energy on a reaction diagram

Question 9

Short-chain saturated fatty acids present in some animal products can produce a rancid odor if they are released from a triglyceride. Which of the following methods would prevent this type of rancidity?

I. Hydrogenation

II. Dehydration

III. Sterilization

Answer 9

II and III are correct.

Hydrolysis releases a free fatty acid from a triglyceride. Without water, hydrolysis can’t happen, so dehydration should be effective in preventing this type of rancidity.

Bacteria often have lipases that catalyze the hydrolysis of the ester linkage between the fatty acid and the triglyceride. Removing bacteria through sterilization should slow hydrolytic rancidity.

Question 10

What will the product be in a hydrogenation reaction of a fully saturated fatty acid?

Answer 10

Hydrogenation will not affect a fully-saturated fatty acid, as there is no double bond to hydrogenate.

Question 11

The typical range of human hearing spans from 20 Hz to 20,000 Hz, and the speed of sound in air is approximately 340 m/s. With this information in mind, an ultrasound signal:

A. must also have a frequency between 20 Hz and 20,000 Hz.

B. must have a frequency lower than 20 Hz.

C. must have a wavelength lower than 0.017 m.

D. must have a wavelength higher than 17 m.

Answer 11

C. must have a wavelength lower than 0.017 m.

The prefix “ultra” means “higher,” as we can discern using our knowledge that ultraviolet light is light with a frequency higher than that of visible light. Ultrasound, then, likely also has a frequency higher than the typical range heard by a human. No answer choice states this directly, so we must calculate the wavelength that this corresponds to. To do so, we can use the simple equation v = λf.

340 m/s = λ(20000 Hz)

3.4 x 10² m/s = λ(2 x 10⁴ Hz)

λ =(3.4 x 10² m/s) / (2 x 10⁴ Hz)

λ =1.7 x 10^-2 m = 0.017 m

Question 12

Velocity (or propagation speed), frequency, and wavelength are universal properties for all waves, and are related by the equation _______

Answer 12

Velocity (or propagation speed), frequency, and wavelength are universal properties for all waves, and are related by the equation v = λf.

Question 13

Mechanical waves require a compressible medium to propagate. Would it be feasible to utilize the Doppler effect to visualize the movement of a planet in a solar system?

A. No, because sound waves are not mechanical waves.

B. No, because the Doppler effect doesn’t apply to non-mechanical waves.

C. Yes, but light would have to be used instead of sound, since sound waves are mechanical.

D. Yes, but light would have to be used instead of sound, since sound waves are non-mechanical.

Answer 13

C. Yes, but light would have to be used instead of sound, since sound waves are mechanical.

Light can be described as electromagnetic waves. These can travel through a vacuum, but mechanical waves cannot, because mechanical waves require a compressible medium to propagate. Notice that it is the difference in frequencies that produces a Doppler effect, not whether the wave is classified as mechanical or non-mechanical.

Question 14

_________ waves are those that involve the actual physical motion of particles, whereas ____________ waves (such as light) can move through vacuum.

Answer 14

Mechanical waves are those that involve the actual physical motion of particles, whereas electromagnetic waves (such as light) can move through vacuum.

Question 15

What differs between the migration rates of small and large molecules when comparing size exclusion chromatography and gel electrophoresis?

Answer 15

In size-exclusion chromatography, smaller particles migrate through the pore system that is present in the agarose stationary phase, while larger particles pass directly through the column. As a result, small molecules migrate more slowly than larger ones.

This differs from gel electrophoresis, in which smaller molecules move more rapidly than large ones through the agarose gel.

Question 16

The inner mitochondrial membrane has a thickness of 5 nm and an average membrane potential of 150 mV. What is the magnitude of the electric field across the mitochondrial membrane in these cells?

A. 3 x 10^-2 V/m

B. 3 x 10⁴ V/m

C. 3 x 10⁷ V/m

D. 3 x 10¹⁰ V/m

Answer 16

C. 3 x 10⁷ V/m

150 mV is equal to 0.15 V. Electric fields across parallel-plate capacitors are measured in N/C or V/m, since one volt = 1 J/C = 1 Nm/C.

E = V/d

E = (0.15 V) / (5 x 10^-9 m) = 3 x 10⁷ V/m.

The general setup of a parallel-plate capacitor is shown below:

Question 17

The two membranes of the mitochondria can be thought of as what kind of structure, in regards to physics?

Answer 17

The mitochondria can be thought of as a parallel plate capacitor

Question 18

The effects of most point mutations can be expected to be ________, but occasionally mutations result in ___________ proteins. This is a major driver of evolution.

Answer 18

The effects of most point mutations can be expected to be negative, but occasionally mutations result in more functional proteins. This is a major driver of evolution.

Question 19

Would Thin-layer chromatography be an effective way to separate enantiomers? Why/Why not?

Answer 19

TLC separates substances based upon differences in their polarities.

Enantiomers share physical properties, including dipole moment, so this method of separation would be ineffective.

Question 20

What is the chemical/physical property utilized by recrystallization?

What kinds of molecules would this technique be useless in separating?

Answer 20

Recrystallization separates substances based upon differences in their solubility.

Enantiomers have identical solubilities (and other physical properties). Therefore, recrystallization would be ineffective in separating enantiomers.

Question 21

Explain the process of recrystallization

Answer 21

Recrystallization is used to purify a solid product that contains impurities.

This process involves the dissolution of the solid in a solvent and subsequent heating. The solid then dissolves and is cooled, causing it to solidify (crystallize) again. As the lattice structures of solids tend to exclude impurities, each subsequent recrystallization results in a progressively purer compound.

Question 22

What chemical/physical property is utilized by centrifugation?

Answer 22

Centrifugation utilizes a rapidly spinning apparatus to separate particles by density.

More dense particles, such as cells, gravitate toward the bottom of the spun tube, while less dense substances remain at the top in a liquid termed the supernatant. This liquid can then be poured off, and further separation or analysis can be conducted.

Question 23

Centrifugation utilizes a rapidly spinning apparatus to separate particles by density.

More dense particles, such as cells, end at the _______ of the spun tube, while less dense substances end at the _______ in a liquid termed the supernatant. This liquid can then be poured off, and further separation or analysis can be conducted.

Answer 23

Centrifugation utilizes a rapidly spinning apparatus to separate particles by density.

More dense particles, such as cells, end at the bottom of the spun tube.

Less dense substances end at the top in a liquid termed the supernatant. This liquid can then be poured off, and further separation or analysis can be conducted.

Question 24

What technique can be utilized to separate a pair of enantiomers?

Answer 24

Chiral resolution

Enantiomers are virtually identical in all of their physical and chemical properties, save for two:

1. They rotate plane-polarized light in opposite directions (but with equal magnitude) and
2. They react differently with certain other chiral molecules. Chiral resolution takes advantage of the latter difference in order to separate mixtures of enantiomers.

Question 25

The lower the energy held by a compound, the ______ stable it is

Answer 25

The lower the energy held by a compound, the more stable it is

Question 26

Researchers used wet column chromatography (nonpolar mobile phase and polar stationary phase) to separate two suspected apoptotic inhibitors. Which statement accurately describes this process?

A. Inhibitor A will elute first because it is more polar than Inhibitor B.

B. Increasing the polarity of the mobile phase will cause Inhibitor B to remain behind in the column.

C. Inhibitor B will elute second because it interacts more favorably with the stationary phase than does the Inhibitor A.

D. Decreasing the affinity of Inhibitor A for the stationary phase will increase its retention time relative to the Inhibitor B.

Answer 26

C. Inhibitor B will elute second because it interacts more favorably with the stationary phase than does Inhibitor A.

From the structures shown in the question, we can see that Inhibitor B has a hydroxyl group in place of the ether group on the phenyl ring. This makes Inhibitor B more polar than Inhibitor A. In column chromatography, Inhibitors A and B will be retained by the stationary phase differently, causing them to move at different speeds and separate from each other while running through the column with the mobile solvent. Since the stationary phase is polar, Inhibitor B will have a higher affinity for this phase and will travel more slowly through the column, causing it to elute second.

Question 27

The most important physiological example of dimerization is how __________ can induce the formation of cross-linking between thymine/thymine and thymine/cytosine pairs in DNA, resulting in carcinogenic structures known as pyrimidine dimers.

Answer 27

The most important physiological example of dimerization is how UV radiation can induce the formation of cross-linking between thymine/thymine and thymine/cytosine pairs in DNA, resulting in carcinogenic structures known as pyrimidine dimers.

Question 28

Is NH₃ a bronstead-lowry base?

Answer 28

Yes. It is capable of accepting a proton, or H atom.

Question 29

Is BF₃ a bronstead-lowry base?

Answer 29

No.

BF₃ is a lewis acid, as it can accept a lone pair of electrons.

Question 30

In the final step of Compound 1 synthesis, Br acts as:

A. the substrate.

B. the nucleophile.

C. the leaving group.

D. the catalyst.

Answer 30

C. the leaving group.

Figure 2 shows that Li and Br disappear from the reactant and a bond is made between C and B in the final step of Compound 1 synthesis. From our knowledge of organic chemistry, halogens are often leaving groups in nucleophilic substitution reactions and Li can act as a base or nucleophile. Br is a halogen and is thus most likely acting as a leaving group, so choice C is correct.

Question 31

Aspartic acid differs from asparagine in that:

A. it contains fewer oxygen atoms.

B. its side chain can hydrogen bond.

C. its side chain does not contain an amide.

D. its side chain does not contain an amine.

Answer 31

C. its side chain does not contain an amide.

Aspartic acid is an acidic amino acid; as such, its side chain contains a –COOH group. In contrast, the side chain of asparagine includes an amide functionality, as shown below:

Question 32

Importantly, the Bernoulli equation indicates that when height is constant (as in a horizontal pipe system), an increase in velocity corresponds to a(n) _______ in pressure, and vice versa.

Answer 32

Importantly, the Bernoulli equation indicates that when height is constant (as in a horizontal pipe system), an increase in velocity corresponds to a decrease in pressure, and vice versa.

Question 33

Describe the relationship between velocity and pressure, according to the Bernoulli equation.

Answer 33

According to the Bernoulli equation, velocity and pressure are inversely proportional.

Question 34

Turbulent flow in humans is a major risk factor for atherosclerosis, the buildup of plaque on arterial endothelium. Ignoring any potential effects of turbulence, what effect would atherosclerosis have on blood flow?

A. Narrowing of the artery causes the velocity to increase and the hydrostatic pressure to decrease.

B. Narrowing of the artery causes the velocity to increase and the osmotic pressure to decrease.

C. Narrowing of the artery causes the velocity to decrease and the hydrostatic pressure to decrease.

D. Expansion of the artery causes the velocity to decrease and the hydrostatic pressure to increase.

Answer 34

A. Narrowing of the artery causes the velocity to increase and the hydrostatic pressure to decrease.

The buildup of plaque in the lumen of the vessel would cause a narrowing of the vessel. The question then implies that we must consider the Venturi effect, which states that a fluid’s velocity must increase as it passes through a constriction, based on the continuity (A₁v₁=A₂v₂) principle. According to the Bernoulli principle, then, the hydrostatic pressure must decrease to conserve energy.

The reason that B is incorrect is as follows: While plaque buildup does cause a narrowing of the vessels and an increase in velocity, the osmotic pressure (determined by the solute composition of the fluid) will not be affected by this narrowing.

Question 35

Why would osmotic pressure be unaffected by the narrowing of a tube?

Answer 35

Osmotic pressure is a colligative property. Colligative properties are determined only by the number of molecules they dissociate, or dissolve, into.

Question 36

During an experiment involving the effect of roller coaster riding on neck muscles, all participants reported a feeling of weightlessness in the loop segment of the roller coaster ride. At which of the following positions did this feeling occur?

A. 1

B. 2

C. 3

D. 4

Answer 36

C. 3

First, draw a free-body diagram for all of the positions. The feeling of weightlessness occurs when the normal force is minimal. At the bottom of the loop, the normal force points toward the center of the loop, while the gravitational force points downward. The net force will be the centripetal force directed toward the center of the circle. At the bottom of the loop, the normal force is largest because in order for the net force to be directed inward, the normal force should exceed the downward gravitational force. At the top of the loop, both the gravitational force and the normal force point downward. At the top of the loop, the normal force is the least because gravity is downward and therefore, there is no need for a large normal force in order to stay in a circular path. At points 2 and 4, the normal force and the gravitational force are perpendicular. Therefore, normal force is still needed in order to sustain the inward centripetal force.

Question 37

A woman is standing two meters away from a speaker. The speaker is turned up to 11 on its dial, and the power of the sound hitting her tympanic membrane increases 100-fold. How far would the woman need to move to reduce the sound back to its original decibel level?

A. 10 m

B. 18 m

C. 20 m

D. 50 m

Answer 37

B. 18 m

The decibel level of sound is given by dB = 10log (I/I_o), where I denotes intensity and I_o is the reference intensity, which represents the lowest intensity audible to the human ear.

In order to have the same decibel level, the same intensity, I, must reach the tympanic membrane. The intensity of sound is given by the equation I = P/A, where P = power and A = area. If the power increases 100-fold, then the area would need to increase by a factor of 100 to maintain the same intensity. The area, A, of the sound wave is given by the surface area of a sphere as the sound travels away from the speaker. The surface area of a sphere is proportional to the radius squared, or r² (A = 4πr²).

So, in order to increase the area 100-fold, the radius, r, must increase by a factor of 10 (10² = 100).

Thus, if the woman originally stands two meters away then to maintain the same decibel level, she needs to stand 2 x 10 = 20 m away from the speaker. Standing 2 m away, the woman must move 18 m to reach a total final distance of 20 m (choice C is a clever trap).

Question 38

What does the length of a molecule indicate about it’s ability to be oxidized?

Answer 38

The length of a molecule does not indicate anything about its ability to be oxidized.

Question 39

What is wrong about this statement:

The starch in animal cells is present in small granules packed together like grapes.

Answer 39

Animal cells do not store starch; instead, they store glucose as glycogen. Plant cells store glucose as starch.

Question 40

Formation of a hemiacetal from a monosaccharide results in a molecule that has the same molecular weight as the original monosaccharide. Formation of an acetal from two monosaccharides results in a molecule that has:

A. a molecular weight that can vary, depending upon where the acetal linkage forms.

B. a molecular weight that is the same as the combined weight of the two monosaccharides.

C. a molecular weight that is 18 amu less than the combined weight of the two monosaccharides.

D. a molecular weight that is 18 amu more than the combined weight of the two monosaccharides.

Answer 40

C. a molecular weight that is 18 amu less than the combined weight of the two monosaccharides.

Formation of a acetal disaccharide requires loss of a molecule of water, so the molecular weight of a disaccharide will be 18 amu (1 O, 2 H) less than the combined mass of the two monosaccharide components. Opening a hemiacetal ring does not require any addition of water.

Question 41

Describe 2 factors that affect the solubility of a gas in a liquid.

Answer 41

As temperature increases → solubility decreases

As partial pressure increases → solubility increases

Gases generally have greater solubility in cooler liquids. Also, the solubility of a gas increases as the partial pressure of the gas increases.

Question 42

the critical fluid velocity (V_c), is defined as the smallest velocity at which turbulent flow will occur.

If an experiment is run in which the velocity is kept constant, which of the following would increase the probability of turbulence?

I. An increase in the diameter in the tube

II. A decrease in the viscosity of the fluid

III. A decrease in the density of the fluid

Answer 42

I and II only

In order to increase the likelihood of turbulence, we would need to lower the threshold at which turbulence occurs, thus making it more likely that the calculated critical velocity will be lower than the constant velocity used in the new experiment. In examining Equation 1, we can see that the critical velocity is inversely related to the diameter of the tube. Therefore, increasing the diameter should decrease the critical velocity (I). Equation 1 also indicates that there is a direct relationship between the fluid viscosity and the critical velocity, so decreasing the viscosity would decrease the critical velocity (II).

Question 43

Which of the following best describes the variables plotted in Figure 1?

A. The inverse of the tube diameter is the independent variable, plotted on the abscissa, and the critical velocity is the dependent variable, plotted on the ordinate.

B. The critical velocity is the independent variable, plotted on the abscissa, and the inverse of the tube diameter is the dependent variable, plotted on the ordinate.

C. The inverse of the tube diameter is the independent variable, plotted on the ordinate, and the critical velocity is the dependent variable, plotted on the abscissa.

D. The critical velocity is the independent variable, plotted on the ordinate, and the inverse of the tube diameter is the dependent variable, plotted on the abscissa.

Answer 43

A. The inverse of the tube diameter is the independent variable, plotted on the abscissa, and the critical velocity is the dependent variable, plotted on the ordinate.

In this case, the independent variable (the variable that is manipulated by the researcher) is the inverse of the diameter, while the dependent, or measured, variable is the critical velocity. By convention, the independent variable is plotted on the abscissa (x-axis) and the dependent variable is plotted on the ordinate (y-axis).

Question 44

By convention, the independent variable is plotted on the ________ (x-axis) and the dependent variable is plotted on the ________ (y-axis).

Answer 44

By convention, the independent variable is plotted on the abscissa (x-axis) and the dependent variable is plotted on the ordinate (y-axis).

Question 45

True or False:

The average kinetic energy of the gas sample depends on the mass of molecules.

Answer 45

False.

KE_gas=(3/2)nRT

Question 46

Describe Archimedes principle

Answer 46

Archimedes’ principle states that the buoyant force is directly proportional to the volume of the liquid.

F_b = ρ_liquidV_liquidg

Question 47

In which of the following aqueous carbohydrate solutions would a given vesicle have the greatest buoyancy?

A. 0.15 M sucrose

B. 0.15 M glucose

C. 0.20 M fructose

D. 0.25 M galactose

Answer 47

A. 0.15 M sucrose

Buoyancy is the force that results from the displacement of fluid when an object is submerged. The magnitude of the buoyant force is equal to the weight of the fluid displaced. Therefore, the greater the density of the solution, the larger the buoyant force. Glucose, fructose, and galactose are all monosaccharides with the molecular formula C₆H₁₂O₆, so their relative densities will depend on their concentrations. The most dense of those three choices, then, is choice D. However, choice A is sucrose, a disaccharide with the formula C₁₂H₂₂O₁₁. Since sucrose has a molecular weight almost twice that of galactose, a 0.15 M sucrose solution would have a density approximately equivalent to that of a 0.3 M galactose solution. Choice D is not this highly concentrated, so we can eliminate it and choose option A.

Question 48

If the average bone mineral density is 3.88 g/cm³, which of the following is a reasonable estimation of the density of the average human body?

A. 0.001 g/cm³

B. 1 g/cm³

C. 3.88 g/cm³

D. 4.88 g/cm³

Answer 48

B. 1 g/cm³

Bones are the most dense part of the human body, so the overall body should have a density lower than 3.88 g/cm³. From this alone, we can eliminate choices C and D. Choice A is a very small number and would suggest that the human body has a density almost as low as air at sea level. Thus, choice B must be correct. We can also consider the fact that humans typically float right at the surface of water, implying that the density of the human body is approximately equal to the density of water.