AAMC CBT8 and 8R OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT8 and 8R.

Please post ONLY questions pertaining to AAMC CBT8 and 8R.
Out of respect for people who may not have completed the other exams, do not post questions or material from any other AAMC exam.

Please see this thread for the rules of order before you post.

Good luck on your MCAT!

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[ThiaminePyroPhosphate]

In regards to passage 5 (the one about the balloon depth vs temp), is the system considered adiabatic? Going over some posts, I've seen people say that no heat is actually transferred between the balloon and the water. How did they come to the conclusion based on the passage?

Thanks

 

[jaybird12]

Also, second question on PS #27: Which of the following would not help in predicting the results shown in Figure 1? (Passage about balloons and depth in tank, and as depth increases, temperature increases)
Choices A and B are easily eliminated
For choice C (variation with depth in the speed of the balloon), the answer explanation makes it seem like it is the speed of the air molecules it is considering. In that case, variation with depth in the speed of the air molecules in the balloon, that makes sense. But does speed of the balloon itself necessarily correlate with the speed of the molecules?

The speed of the balloon itself shouldn't correlate with the speed of the molecules. I think someone already put this, but the Kaplan answer key says, "Since speed is an indication of kinetic energy and temperature, its variation will affect temperature, thus serving as another predictive component". The problem is, the actual question seems to be talking about the balloon's uniform velocity through the water, NOT the random translational velocity of the air molecules inside the balloon. And temperature is not based on an object's uniform velocity, but on the random velocity (and thus KE) of the actual molecules within the object (ie, internal energy). So you can have an object moving really fast but still be at a low temperature because the molecules are not moving very much within the object, or an object sitting still at a high temperature.
I can't remember for the life of me where it was (an EK book probably, or possibly AMCAS test), but just last week, I answered a question that asked about how you could increase the temperature of an object. And the point of the question was that you CANNOT increase an objects temperature by increasing its uniform velocity (picking it up and moving it).
So I don't know, both C and D seem like they could be correct to me. Although D is more obviously correct, I suppose.

 

[jaybird12]

In regards to passage 5 (the one about the balloon depth vs temp), is the system considered adiabatic? Going over some posts, I've seen people say that no heat is actually transferred between the balloon and the water. How did they come to the conclusion based on the passage?

I don't know if it would be fair to say that the system is completely adiabatic, but there must be some resistance to heat flow. As the balloon moves down deeper into the water, the force from the water pressure does work on the balloon, raising the energy of the molecules. If you raise the energy of gas molecules, the temperature increases, as we can see in the graph. But, as #27 brings up, if the rubber can conduct heat to the water, the increase in temperature might not be very much. (That's why for that question, it's helpful to know if the rubber does or does not conduct heat). In fact, if the rubber could conduct heat freely, then any increase in energy/temperature of the balloon's air would just mean that the heat would start flowing freely from the warmer balloon to the colder water until they were the same temperature again; in which case, the balloon temperature would stay the same at all depths. Obviously, the graph shows that the temperature DOES depend on the depth, so there must be some resistance to heat flow, and the system must be at least partially adiabatic.

 

[Shirafune]

Could somebody explain #100 again? I've tried reading some of the other explanations. I just don't understand how to interpret the data to come to that conclusion. Maybe I can give it a try and then have somebody verify?

Which semicarbazone is the product of thermodynamic control?

Cyclohexanone - MP 166C
2-Furaldehyde - MP 202C

When temperatures are high enough, there is an "excess" of kinetic energy and the activation barrier isn't enough to dictate kinetic control. Therefore, at high temperatures, thermodynamic control predominates. When looking at the experimental data, it shows that as the reaction temperature is increased, the MP of the product increases toward that of 2-Furaldehyde.

"2-Furaldehyde's, because it is produced under equilibrium conditions and is more stable than the other product" is the best answer because the semicarbazone of 2-Furaldehyde is clearly under thermodynamic control and because the product would have lower potential energy if it were under thermodynamic control? Similarly, the correct answer lists that the product is more stable (less potential energy).

Also, for #116, does anybody have another explanation for it? The AAMC answer just seems like bs. I got it right, but I was wondering if anybody else had a better explanation.

Some animals have developed the ability to excrete nitrogenous waste largely in the form of uric acid, which is nontoxic and does not require large amounts of water for its excretion. Considering its lifestyle, what animal would excrete nitrogen primarily in the form of uric acid?

(A) Wild pig - INCORRECT because the passage states that "in most other mammals, uric acid is further oxidized to allantoin before excretion"
(B) Flying bird - CORRECT by process of elimination
(C) Carnivorous shark - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the shark's environment
(D) Herbivorous bony fish - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the fish's environment

 

[Marleywh]

Well, the idea is that we don't have any information about whether or not the female lizards have the pigment. The passage says that UV pigment is located in the dewlap, but it doesn't identify any gene linkage that relates the two.



Agreed. Absolutely agreed. Absolutely, absolutely agreed. I had qualms with the entire passage actually.

Well you have to think about evolutionary mechanisms. Would the environment be decided by their UV signaling abilities, or would their UV abilities be decided by the environment? You cannot conclude that the environment is effected by the lizards phenotypes, but must conclude the reverse.

 

[justadream]

PS #40

How do you know CO2 evolves rather than like SO3?

 

[justadream]

If speed is the same, how you know that frequency and wavelength change?

 

[Marleywh]

Well we know that speed doesn't change, because it is entirely dependent on the medium. We also know that frequency does change because of the Doppler effect, so if frequency changes, and speed is constant, then wavelength has to change as well.

 

[Oh_Gee]

unsure where "g" is coming from but I understand the question.

The internal resistance of a battery is a "flaw" that basically every battery has. (Not really a flaw, it's mostly just aging of the battery that causes the terminal voltage drop. Temperature can change it too but I'm not too sure how).

The battery itself has an impedance, before the net voltage can get to the rest of the circuit. The battery is not 100% efficient.

Therefore, the "terminal voltage" (ie- the NET voltage experienced by the rest of the circuit) will be less than than a 100% efficient/ideal.

The voltage could not be increased (or you would have an infinite energy source), only decreased. Thus B is correct.

but where the 1/4 come from???

 

[Oh_Gee]

if there's no more PTH, then there's no more calcium resorption from the bone so wouldn't that change the ratio of mineral to matrix tissue

 

[Oh_Gee]

PS #40

How do you know CO2 evolves rather than like SO3?

i just guessed on that one.. a lot of problems that ask that usually, the answer is CO2. i guess just memorize acid + a carbonate gives off CO2 gas

 

[Oh_Gee]

I'm not quite sure what you're confused about, but I'll take a stab at the question...

Regardless of whether the product of the reaction is the kinetic one or the thermodynamic one, it'll have a reaction profile. Think back to collision theory... in reactions, molecules collide and they'll react. However, it was shown that for most reactions, the frequency of collisions was much higher than the number of collisions that resulted in products. It's more than just collisions, you need both molecules to have an adequate amount of energy (activation energy) and they need to be appropriately oriented (spatially). Think Arrhenius equation. The activation energy is independent of the temperature, however, different reaction pathways require different activation energies. Remember, systems that are in equilibrium does NOT mean that reactants have stopped converting to products. It means that the rate of reactants turning to products is EQUAL to the rate of products turning into reactants. This is why thermodynamic products will form (but generally take longer). Because the activation energy is higher for thermo products, the rate at which the products turn back into reactants is considerably smaller.

A.) Irrelevant.
B.) The rate of formation is always dependent on the path.
C.) This is the right answer; the kinetic product typically has the lower energy of activation, which is why it's faster.
D.) Higher energy of activation would mean that it would take longer for the reactant to turn into the product. Think of climbing a 100 foot hill vs. 200 foot hill... it would be quicker to climb the 100 foot hill.

how is Ea not dependent on temp?

 

[Heday]

how is Ea not dependent on temp?

Arrhenius equation implies that k is dependent on temperature, no Ea. I don't remember my train of thought when I wrote the post, but activation energy should be independent of temp for a specific reaction pathway because it would be a state function. whether the temperature is 100 degrees or 0 degrees, any molecule within a reaction will require X amount of energy to begin its journey in the reaction pathway. maybe you're confusing the actual energy of molecule and the activation energy of a reaction pathway for a molecule.

 

[Oh_Gee]

Arrhenius equation implies that k is dependent on temperature, no Ea. I don't remember my train of thought when I wrote the post, but activation energy should be independent of temp for a specific reaction pathway because it would be a state function. whether the temperature is 100 degrees or 0 degrees, any molecule within a reaction will require X amount of energy to begin its journey in the reaction pathway. maybe you're confusing the actual energy of molecule and the activation energy of a reaction pathway for a molecule.

even though you can rearrange the equation to show

Ea=RT ln(k/A)?

i'm a little fuzzy on state functions. could you elaborate more? thanks for the help. i know your post is old.
i just took this today

 

[Aerus]

even though you can rearrange the equation to show

Ea=RT ln(k/A)?

i'm a little fuzzy on state functions. could you elaborate more? thanks for the help. i know your post is old.
i just took this today

The activation energy is dependent on how much energy is needed. By increasing the temperature, you provide more of that needed energy. It's like getting to the top of the hill. Some hills require more protein bars. Some require less. But you can't change the height of that hill by altering the amount of protein bars you eat.

 

[DrDreams]

right It asks about it according to aristotles theory. His theory was that constant velocity is determined through the object pushing air behind it filling up the space it originally had. Thus if a more massive object were used, it would be able to effective "push" more air behind it, giving it a higher constant speed.

Alternatively you could look at it from a common sense perspective. Before Newton and gravity, the common person would have thought that a heavier object falls faster than a lighter object.

So here is what I don't get.

Since terminal velocity is the maximum velocity it can reach before being at a constant velocity.
Since t α 1/W right?

Then higher the W the lower the time correct?

Then v=vot+at. Is not time and velocity then proportional? I had originally chosen the correct answer, then went back and did this analysis and chose the wrong one.

Need some explanation please.

 

[DrDreams]

Could somebody explain #100 again? I've tried reading some of the other explanations. I just don't understand how to interpret the data to come to that conclusion. Maybe I can give it a try and then have somebody verify?

Which semicarbazone is the product of thermodynamic control?

Cyclohexanone - MP 166C
2-Furaldehyde - MP 202C

When temperatures are high enough, there is an "excess" of kinetic energy and the activation barrier isn't enough to dictate kinetic control. Therefore, at high temperatures, thermodynamic control predominates. When looking at the experimental data, it shows that as the reaction temperature is increased, the MP of the product increases toward that of 2-Furaldehyde.

"2-Furaldehyde's, because it is produced under equilibrium conditions and is more stable than the other product" is the best answer because the semicarbazone of 2-Furaldehyde is clearly under thermodynamic control and because the product would have lower potential energy if it were under thermodynamic control? Similarly, the correct answer lists that the product is more stable (less potential energy).

Also, for #116, does anybody have another explanation for it? The AAMC answer just seems like bs. I got it right, but I was wondering if anybody else had a better explanation.

Some animals have developed the ability to excrete nitrogenous waste largely in the form of uric acid, which is nontoxic and does not require large amounts of water for its excretion. Considering its lifestyle, what animal would excrete nitrogen primarily in the form of uric acid?

(A) Wild pig - INCORRECT because the passage states that "in most other mammals, uric acid is further oxidized to allantoin before excretion"
(B) Flying bird - CORRECT by process of elimination
(C) Carnivorous shark - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the shark's environment
(D) Herbivorous bony fish - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the fish's environment

Was #100 and aldol condensation reaction. I have no idea...I am waiting for an explanation on this one as well.



Here is some speculation
So after they collected all of the crystals right, they were all semicarbazones. And if you look at the data, the 2-furaldehyde and cyclohexanone are also semicarbazones. Flask D had the cyclohexanone semicarbazone product.

Flask E had the 2-furaldehyde semicarbazone product. Since the literature melting point of the 2-furaldehyde was 202 and flask E was the closest to that. We had to invest the most energy in flask E for it to melt.

Thermodynamic products are more stable than kinetic products (from what I remember from orgo, correct me if I am wrong) and hence, since E is the semicarbazone of 2-furaldehyde and had the highest melting point, it MUST be the thermodynamic product. The thermodynamic product looks like its more branched, and higher branching increases melting point but decreases boiling pointIf I was not panicking I think I would have gotten that...

 

[justadream]

Could somebody explain #100 again? I've tried reading some of the other explanations. I just don't understand how to interpret the data to come to that conclusion. Maybe I can give it a try and then have somebody verify?

Which semicarbazone is the product of thermodynamic control?

Cyclohexanone - MP 166C
2-Furaldehyde - MP 202C

When temperatures are high enough, there is an "excess" of kinetic energy and the activation barrier isn't enough to dictate kinetic control. Therefore, at high temperatures, thermodynamic control predominates. When looking at the experimental data, it shows that as the reaction temperature is increased, the MP of the product increases toward that of 2-Furaldehyde.

"2-Furaldehyde's, because it is produced under equilibrium conditions and is more stable than the other product" is the best answer because the semicarbazone of 2-Furaldehyde is clearly under thermodynamic control and because the product would have lower potential energy if it were under thermodynamic control? Similarly, the correct answer lists that the product is more stable (less potential energy).

Also, for #116, does anybody have another explanation for it? The AAMC answer just seems like bs. I got it right, but I was wondering if anybody else had a better explanation.

Some animals have developed the ability to excrete nitrogenous waste largely in the form of uric acid, which is nontoxic and does not require large amounts of water for its excretion. Considering its lifestyle, what animal would excrete nitrogen primarily in the form of uric acid?

(A) Wild pig - INCORRECT because the passage states that "in most other mammals, uric acid is further oxidized to allantoin before excretion"
(B) Flying bird - CORRECT by process of elimination
(C) Carnivorous shark - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the shark's environment
(D) Herbivorous bony fish - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the fish's environment

With regard to your first question, I believe you could figure it out by looking at what the major product is under HOT conditions. This will be the thermodynamic product.


With regard to your second question - just use common sense. Uric acid is super concentrated and doesn't require being dissolved in a solvent (at least I don't think so). Thus, you can carry it without it being so heavy. It's a big advantage for birds to use uric acid because they need to be lightweight to fly. Think about what would happen if birds excreted urea in the form of urine. They'd probably fail to fly efficiently.

 

[justadream]

Was #100 and aldol condensation reaction. I have no idea...I am waiting for an explanation on this one as well.



Here is some speculation
So after they collected all of the crystals right, they were all semicarbazones. And if you look at the data, the 2-furaldehyde and cyclohexanone are also semicarbazones. Flask D had the cyclohexanone semicarbazone product.

Flask E had the 2-furaldehyde semicarbazone product. Since the literature melting point of the 2-furaldehyde was 202 and flask E was the closest to that. We had to invest the most energy in flask E for it to melt.

Thermodynamic products are more stable than kinetic products (from what I remember from orgo, correct me if I am wrong) and hence, since E is the semicarbazone of 2-furaldehyde and had the highest melting point, it MUST be the thermodynamic product. The thermodynamic product looks like its more branched, and higher branching increases melting point but decreases boiling pointIf I was not panicking I think I would have gotten that...

I'm not sure if you are supposed to be looking at MP to determine kinetic vs. thermodynamic (never heard of anyone doing that).

However, this drawing (assuming it's correct) would show you why the molecule on the right is thermodynamic. It has the more substituted alkene. More substituted alkenes are more stable. More stable = thermodynamic product.

 

[DrDreams]

I'm not sure if you are supposed to be looking at MP to determine kinetic vs. thermodynamic (never heard of anyone doing that).

However, this drawing (assuming it's correct) would show you why the molecule on the right is thermodynamic. It has the more substituted alkene. More substituted alkenes are more stable. More stable = thermodynamic product.

Yea thats what I thought, but that is what examkrackers Orgo told me...

That drawing however, is from TBR.

 

[Shirafune]

Yea thats what I thought, but that is what examkrackers Orgo told me...

That drawing however, is from TBR.

You have an extra bond on one of your alkene carbons.
Haha. I'm too lazy to go back to the problem right now, but I remember not being able to draw the molecule so I could only rely on the data/passage.

 

[justadream]

@DrDreams
@Shirafune

I just took a look at the passage again. The MP has NOTHING to do with thermodynamic/kinetic. It's only used to identify which product your formed under different conditions. AAMC doesn't just want to give you the major product (that'd be too easy).

The data clearly tells you why 2-Furaldehyde is the thermodynamic product. In fact, both experiments make this conclusive.

Look at experiment 1. As you increase temperature conditions, you form more of 2-Furaldehyde. Thus, 2-Furaldyhude must be the thermodynamic product.

In experiment 2, you perform both trials at high temperature. The product of both is 2-Furaldehdyde.

 

[DrDreams]

You have an extra bond on one of your alkene carbons.
Haha. I'm too lazy to go back to the problem right now, but I remember not being able to draw the molecule so I could only rely on the data/passage.

Do I really? I wouldn't doubt it man, Burn out is really starting to set in.

 

[DrDreams]

@DrDreams
@Shirafune

I just took a look at the passage again. The MP has NOTHING to do with thermodynamic/kinetic. It's only used to identify which product your formed under different conditions. AAMC doesn't just want to give you the major product (that'd be too easy).

The data clearly tells you why 2-Furaldehyde is the thermodynamic product. In fact, both experiments make this conclusive.

Look at experiment 1. As you increase temperature conditions, you form more of 2-Furaldehyde. Thus, 2-Furaldyhude must be the thermodynamic product.

In experiment 2, you perform both trials at high temperature. The product of both is 2-Furaldehdyde.

You know, I really do hate that passage. But not as much as the student teacher one from verbal in 7.

 

[justadream]

You know, I really do hate that passage.

Haha it was one of my favorites because I understood everything. Now some of the physics passages I've seen.....(optics, waves, weird E &M stuff).....that's another story.

 

[DrDreams]

Haha it was one of my favorites because I understood everything. Now some of the physics passages I've seen.....(optics, waves, weird E &M stuff).....that's another story.

You know I got all of them except this single one right and for some odd reason I changed my singlet andswer to a doublet. Even though I knew it was a singlet.

During the bio section, I begin to have pretty intense back pain...I am not getting used to it. At the same time, my strongest section is Bio.

My weakest section right now, is fluids.

 

[justadream]

You know I got all of them except this single one right and for some odd reason I changed my singlet andswer to a doublet. Even though I knew it was a singlet.

During the bio section, I begin to have pretty intense back pain...I am not getting used to it. At the same time, my strongest section is Bio.

My weakest section right now, is fluids.

I suck at fluids too. However, only TBR is proficient at exposing my weaknesses in it (so far at least).

 

[DrDreams]

I suck at fluids too. However, only TBR is proficient at exposing my weaknesses in it (so far at least).

You know I haven't even had a chance to do the problems in TBR. Ive been doing AAMC exams. And its been helping me so far...

 

[erythrocyte666]

Can someone explain why PS #8 (Passage II: MRI) is B and not A?
X-ray imaging sometimes requires contrast dyes. In MRI, dyes are:
A: less toxic
B: not always needed but sometimes helpful

I thought A made sense since beginning of passage says MRIs are less invasive than X-rays. I know that doesn't necessarily imply toxicity, but after skimming the passage again I find a couple things: 1) no mention of dyes in MRIs and 2) whole point of MRIs is combinations of magnetic fields acting on tissue H atoms, which I assumed to be inherently different from dye-based imaging. So if either choice made some sense, I felt it was A.

 

[MelloTangelo]

Can someone explain why PS #8 (Passage II: MRI) is B and not A?
X-ray imaging sometimes requires contrast dyes. In MRI, dyes are:
A: less toxic
B: not always needed but sometimes helpful

I thought A made sense since beginning of passage says MRIs are less invasive than X-rays. I know that doesn't necessarily imply toxicity, but after skimming the passage again I find a couple things: 1) no mention of dyes in MRIs and 2) whole point of MRIs is combinations of magnetic fields acting on tissue H atoms, which I assumed to be inherently different from dye-based imaging. So if either choice made some sense, I felt it was A.

Ah, I remember that passage. This is my take on the answer. MRI is less invasive than X-rays because of their use of radio waves, but dyes will be most likely be the same regardless of the imaging technique used. So while MRI is less invasive, an imaging dye won't be any different between the two. With X-Rays, dyes are often necessary because the contrast of image isn't enough. With MRI, a high-contrast image is often produced, so they aren't always necessary, but since they can increase the contrast, they can be helpful if an image isn't as clear as one would like.

Hopefully that makes a little sense!

 

[erythrocyte666]

Ah, I remember that passage. This is my take on the answer. MRI is less invasive than X-rays because of their use of radio waves, but dyes will be most likely be the same regardless of the imaging technique used. So while MRI is less invasive, an imaging dye won't be any different between the two. With X-Rays, dyes are often necessary because the contrast of image isn't enough. With MRI, a high-contrast image is often produced, so they aren't always necessary, but since they can increase the contrast, they can be helpful if an image isn't as clear as one would like.

Hopefully that makes a little sense!

Thanks for the explanation. I agree but the passage doesn't seem to even imply that dyes are used in MRI - the passage seems to focus exclusively on the magnetic fields acting on H atoms already within human tissue.

 

[Janus_Kinase]

For #40PS I cant find a clear explanation. I have these "which gas will form" problems before and got them wrong lol. Does anyone have a trick to solving these??

 

[Gauss44]

Criticism of VR Passage 2 about Literary Study

I'm wondering what non-science majors think of this opinion? - An MCAT student of mine who was a literature major found the first three-and-a-half paragraphs of passage 2 to be negative and maybe mildly defamatory toward authors of literature, labeling their work as non-intellectual or requiring less intelligence**, and the study of their work as unoriginal and deficient, compared to the supreme and "triumphant" methods of science. In that sense, she feels that that passage gives the group discussed favorably an advantage* because it's easier to read (or listen to and comprehend) something that is flattering, than something that is perceived as being negative and unfair - and in that sense, creates a disparity. (The passage then, sort of rebounds to the negative theme of inferiority in the last paragraph, labeling non-scientific achievements as, obscure or less popular...) If other people feel this way I might bring it to AAMC's attention in case they want that on their radar.

(Mods, I believe that this thread is the correct place for this post. I think the rule is any topic that discusses AAMC exams goes in the official thread. Feel free to correct me if I am wrong.)

*Acknowledgement: An advantage on this passage and an inflated practice test score, could be a disadvantage overall.

**Theme is "echoed" in question #60.

 

[homycraz2]

Some animals have developed the ability to excrete nitrogenous waste largely in the form of uric acid, which is nontoxic and does not require large amounts of water for its excretion. Considering its lifestyle, what animal would excrete nitrogen primarily in the form of uric acid?

(A) Wild pig - INCORRECT because the passage states that "in most other mammals, uric acid is further oxidized to allantoin before excretion"
(B) Flying bird - CORRECT by process of elimination
(C) Carnivorous shark - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the shark's environment
(D) Herbivorous bony fish - INCORRECT because the vignette states that the animal should not require large amounts of water, which contradicts the fish's environment

Nitrogenous wastes... bad see. Don't want them in the body see?
Uric acid formation is nontoxic... see.
Doesn't need lots of water... see.

Fish and shark are literally swimming in water. Using water ain't a concern see.
Wild pig, he lives on land. He mammal. He don't make Uric Acid. See?

Flying bird. He fly. Water Heavy. He don't want to carry lots water to live. See. He find way to **** on your car to remove waste using little water. He damage paint. see?

 

[ahisma]

Question on #104: if aldosterone levels are abnormally high why couldn't a healthy kidney respond to the ANP that would be released to lower blood pressure? That's what I thought Hypothesis B was describing anyways.

I figured shortage of insulin would cause persistently higher plasma glucose and thus higher blood volume and pressure. But I guess the kidneys could respond by increasing clearance of glucose somehow or am I missing something here? Kaplan 's explanation says shortage of insulin "has nothing to do with blood pressure" but I thought it increases osmotic pressure and thus blood volume?

Appreciate any help with this, thanks!

 

[Cawolf]

@ahisma

When I solved this problem, I just looked for the only change that would lead to hypertension.

I agree with you on insulin's possible effect but it is important to note that choice B, an excess of glucagon - would result in physiologically similar effects. This makes choices B and D essentially the same and easy to rule out. I think that this observation is what makes the answer less of a grey area if someone doesn't know all of the exact effects.

Generally increased vascular volumes are associated with ions or proteins that have high osmotic or high oncotic pressures, glucose is neither.

 

[ahisma]

Thanks for clearing that up for me. Maybe one of these days I will stop overanalyzing.

 

[blkgrnblkylw]

Question 19 says something along the lines of:
Galileo could have dropped a ball from 10 meters, but instead used a 10 meter inclined plane. What advantage does this have?
a) smaller final velocity
b) greater final velocity
c) longer travel time
d) shorter travel time

C is the correct answer, however I am unsure how A couldn't also be considered correct.

supposed the angle was 30 degrees. sin30 is .5, times the acceleration due to gravity = approximately 5
if we used the equation vf^2 = vi^2 + 2ad, then wouldn't vf be less on an incline plane then dropping from gravity? But if you used the equation d = 1/2at^2, then you could assume that t had to be longer?

The answer stem states the vf will be the same, but I don't understand how. The only thing I am uncertain of is when the question states a 10 meter inclined plane, do they mean the length of the inclined plane that the ball would travel is 10 meters, meaning d is constant. Or do they mean that the top of the plane is 10 meters from the ground, and thus d would vary depending on the angle of the plane? I assumed the former, and that d was constant. If the questions implies that the top of the plane is always 10 meters from the ground then I understand that vf would be the same due to conservation of energy

 

[Cawolf]

If using an inclined plane, the distance traveled will be longer - if friction is absent the final velocity will be the same. They have the same initial PE and if it is all converted to KE, the path it takes does not matter.

It is saying the initial height is the same.

 

[blkgrnblkylw]

If using an inclined plane, the distance traveled will be longer - if friction is absent the final velocity will be the same. They have the same initial PE and if it is all converted to KE, the path it takes does not matter.

It is saying the initial height is the same.

haha, I was hoping you would be answering.

What in the question made you know that initial height is the same? "Galileo could have allowed spheres to drop from a height of 10 m rather than using the 10 m inclined plane described in the passage"

 

[Cawolf]

haha, I was hoping you would be answering.

What in the question made you know that initial height is the same? "Galileo could have allowed spheres to drop from a height of 10 m rather than using the 10 m inclined plane described in the passage"

Thanks!

The passage states that he was using the plane to model free-falling objects, I took that as indication that the height was 10 m. From an experimental design standpoint, that is the most reasonable view.

I do agree it has odd wording - I think it would be clearer to state it is a "10 m high" inclined plane.

Another note, if the plane was 10 m long - we could say nothing about the velocity without knowing the angle - making choices A and B impossible to state with certainty.

 

[OrangeMed]

BS #100
I understand that thermodynamically stable products state dependent and are supposed to be stable because of less Gibbs Free energy, but can anyone please explain how the decision between cyclohexanone and 2-Furaldehyde was made? Is it a rule-of-thumb that compound with higher melting point is more stable?

Thank you!

 

[OrangeMed]

Can someone please also explain BS section #129? What DO you need to determine the location of a gene?
In #131, what makes B the best answer? I thought A can be a possible answer too and since it is more broad, I thought it would fit the question scope better.

 

[Cawolf]

For #131 - habitat is not determined by the dewlap, but the habitat selects for the dewlap. That makes the statement in A wrong.

 

[plage noire]

Thanks!

The passage states that he was using the plane to model free-falling objects, I took that as indication that the height was 10 m. From an experimental design standpoint, that is the most reasonable view.

I do agree it has odd wording - I think it would be clearer to state it is a "10 m high" inclined plane.

Another note, if the plane was 10 m long - we could say nothing about the velocity without knowing the angle - making choices A and B impossible to state with certainty.

The way I understood this question was that the inclined plane was actually 10 m long and not that it was at a height of 10 m. This means that the spheres will have a smaller acceleration than g (equal to g*sin theta) and a smaller final velocity (as in choice A). But, the question isn't asking which of these things happen, it's asking what the "main advantage" of using a plane like this is his experiment is. The main advantage is that since it takes longer for the spheres to travel the 10 m, there is a smaller error in every calculation of the d to t^2 ratio, making all of the measurements more accurate. Choice A is correct in that there is a smaller final velocity, but it's not the best answer to the question because there is no inherent "advantage" in that since he's only measuring time, not velocity.

 

[doubledoctordoubletrouble]

I would like to discuss #60 from the passage about literature and literary study:
According to the passage, the job of the student of literature is to:
1) discover ways to approach literature intellectually
2) separate the rational from the irrational elements in literary works
3) integrate the experience of literature as art and the analysis of literature as knowledge

The answer is only (1), but I marked down both (1) and (2).

In the passage, it states: "It may be true that the subject matter is irrational, or at least contains strongly unrational elements, but the student of literature will not be therefore in any other position than the historian of painting of the musicologist or, for that matter, the sociologist or the anatomist."

I took that to mean that the student, as well as the historian/musicologist/etc are responsible for combing through the irrational elements in their respective bodies of work and identifying the rational elements, which would then allow them to approach literature intellectually...

but according to the answer key, this answer is wrong because it is not explicitly stated in the passage that the student needs to separate the rational and the irrational...

I supposed I agree with that, but then again, in many other questions, we are required to extrapolate information that is not explicitly stated in order to arrive at the correct answer... so uh... how are we supposed to know when to rely on the text as it is written or whether we can extrapolate other meaning? Am I just overthinking this? Thoughts...?

 

[Yorick]

I would like to discuss #60 from the passage about literature and literary study:
According to the passage, the job of the student of literature is to:
1) discover ways to approach literature intellectually
2) separate the rational from the irrational elements in literary works
3) integrate the experience of literature as art and the analysis of literature as knowledge

The answer is only (1), but I marked down both (1) and (2).

In the passage, it states: "It may be true that the subject matter is irrational, or at least contains strongly unrational elements, but the student of literature will not be therefore in any other position than the historian of painting of the musicologist or, for that matter, the sociologist or the anatomist."

I took that to mean that the student, as well as the historian/musicologist/etc are responsible for combing through the irrational elements in their respective bodies of work and identifying the rational elements, which would then allow them to approach literature intellectually...

but according to the answer key, this answer is wrong because it is not explicitly stated in the passage that the student needs to separate the rational and the irrational...

I supposed I agree with that, but then again, in many other questions, we are required to extrapolate information that is not explicitly stated in order to arrive at the correct answer... so uh... how are we supposed to know when to rely on the text as it is written or whether we can extrapolate other meaning? Am I just overthinking this? Thoughts...?

"According to the passage" is the key phrase. Other questions ask you to infer or "the passage suggests." I is clearly stated as a job of the student.

Also I think your interpretation of that sentence is, no offense, completely wrong. Before that, the author writes "assimilate it to a coherent scheme which must be rational if it is to be knowledge." This means that the student's analysis of the literature must be rational regardless of whether the literature itself is rational or irrational, which is much like the job of historians, sociologists, etc.

 

[HotDoc212]

This was asked earlier but can somebody explain this question?

 

[Cawolf]

The buffer equation should be something you are familiar with.

2H+ + CO3^2- ---> H2CO3 ---> H20 + CO2

(all steps reversible)

They had an excess of protons (HCl) and Carbonate. This will form Carbonic acid which then evolves to water and carbon dioxide.

 

[quicheduty]

If some kind person would help clarify a tiny detail in this problem (#119, orgo) I would be so grateful!
Which of the following is the most plausible explanation for the fact that the saponification of the triacylglycerol in the passage resulted in four different fatty acid salts?

Answer: One of the fatty acid salts was unsaturated, and a small percentage isomerized under the reaction conditions

In the procedure, did they take multiple molecules of triacylglycerol to saponify? And by finding that some of the FAs had cis while other had trans double bonds, that's where the fourth peak showed up? I remember struggling with this question because the passage says they purified "a pure triacylglycerol" so I assumed it was one molecule, and I was very confused. Although by logical thinking it'd be unlikely to just do a test on one single molecule. Can't tell if I'm missing something or if I just misunderstood.