AAMC CBT5 and 5R OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT5 and 5R.

Please post ONLY questions pertaining to AAMC CBT5 and 5R.
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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[Dr Gerrard]

To do 31, you need the pH of the solution. Then you just use Henderson Haselbalch.

For 11, this is how I did it.

Volume displaced is the same in both of them, since the object is totally immersed.

Benzene --- 5 = rho * g * V
Fluid --- 12 = rho * g * V

rho for benzene = 0.7

g*V is the same for both fluids

5/0.7 = 12/rho

rho = SG of fluid = 84/50 = 1.7

 

[SuperSaiyan3]

Why would it not satisfy Huckel's rule? It's got a benzene ring!

 

[austinap]

Why would it not satisfy Huckel's rule? It's got a benzene ring!

Who says it isn't?

 

[loveoforganic]

It absolutely has an aromatic component.

 

[G1SG2]

Why would it not satisfy Huckel's rule? It's got a benzene ring!

Hey...that's a question from AAMC 5...I think you should post it in the AAMC 5 thread...

And it's not aromatic because the phenyl group is a substituent. It's considered an aliphatic compound.

 

[ksmi117]

Merging with the AAMC 5 thread.

 

[austinap]

Hey...that's a question from AAMC 5...I think you should post it in the AAMC 5 thread...

And it's not aromatic because the phenyl group is a substituent. It's considered an aliphatic compound.

What is the actual question? That sounds too misleading to be an MCAT question... some context would be nice.

 

[G1SG2]

What is the actual question? That sounds too misleading to be an MCAT question... some context would be nice.

I don't remember exactly how it was worded (maybe the poster can post the exact question) but I think it was which one of the following are aromatic compounds, and benzylamine was paired up with aniline in one of the answer choices (which was a wrong answer choice). The explanation said benzylamine isn't aromatic, but is a phenyl substituted aliphatic amine. I thought it was a weird question.

 

[wanderer]

I don't remember exactly how it was worded (maybe the poster can post the exact question) but I think it was which one of the following are aromatic compounds, and benzylamine was paired up with aniline in one of the answer choices (which was a wrong answer choice). The explanation said benzylamine isn't aromatic, but is a phenyl substituted aliphatic amine. I thought it was a weird question.

benzylamine is aromatic but it is not an aromatic amine, which is what the question was asking about.

 

[G1SG2]

benzylamine is aromatic but it is not an aromatic amine, which is what the question was asking about.

Yeah, I think that was it.

 

[vandyam]

Did anyone feel like this test just blew? Sorry to be harsh, but I'm disappointed. I'm going to take like 3-4 days off from taking FLs b/c I'm soo burnt. This was my 3rd FL in 5 days and I really feel like it was just too much. I've gotten like 5-6 hrs sleep the last couple of nights, and that coupled w/ this just made my score drop a ton.

I got a 36/35 on AAMC 3/4 and this one was a freaking 29. I haven't gone over it yet so I can't tell if it's b/c I didn't know the material, or b/c I just wasn't feeling the exam at all. I hit the 'pause' button like a 100 times, and it took me like 6 hrs to get through it. I kept having to take a break b/c I just couldn't stand to look it any longer.

Did everyone find this exam overall harder than the first two? Guess I'll see when I take FL6/when I go over this one. My VB brought me down (8), so hopefully it'll be lack of concentration.

[/rant]

 

[puravida85]

.....Did everyone find this exam overall harder than the first two? Guess I'll see when I take FL6/when I go over this one. My VB brought me down (8), so hopefully it'll be lack of concentration.

[/rant]

Hey man, this test was a b-otch. I felt like I was calculating the whole time in PS. Also a few of the BS passages were pretty gnarly! I usually get 10's and up on BS but I got an 8! I'm taking the test in a week. We'll see how things go. But, if I were you, chill out. Get some sleep, exercise, and try to forget about this little glitch.

 

[vandyam]

Hey man, this test was a b-otch. I felt like I was calculating the whole time in PS. Also a few of the BS passages were pretty gnarly! I usually get 10's and up on BS but I got an 8! I'm taking the test in a week. We'll see how things go. But, if I were you, chill out. Get some sleep, exercise, and try to forget about this little glitch.

Thanks a lot man. I'm going to try and do that. I can't help but to study these next four days, but I'm def not taking any more FLs until then. Glad someone else found this one to be crazy tho. GL on your exam!

 

[puravida85]

An object that is totally immersed in benzene (specific gravity = 0.7) is subject to a buoyancy force of 5 N. When the same object is totally immersed in an unknown liquid, the buoyancy force is 12 N. What is the approximate specific gravity of the unknown liquid?

The answer is 1.7. Which formula did you guys use? I'm curious to see how people went about this one. I tried to manipulate a couple formulas but didn't see the relationship. I suck at liquids.

 

[SuperSaiyan3]

An object that is totally immersed in benzene (specific gravity = 0.7) is subject to a buoyancy force of 5 N. When the same object is totally immersed in an unknown liquid, the buoyancy force is 12 N. What is the approximate specific gravity of the unknown liquid?

The answer is 1.7. Which formula did you guys use? I'm curious to see how people went about this one. I tried to manipulate a couple formulas but didn't see the relationship. I suck at liquids.

you have to realize that the MCAT likes to test you on the CONCEPTS. They hardly make you do a lot of calculations.

For this question, I simply used what I know about SG and density, as well as buoyant force, to guess what the SG would be.

So we know that Buoyancy = density of FLUID x volume of OBJECT x gravity.

If the buoyancy of the object increased in that FLUID, whereas the normal SG was 0.7, then obviously the density of FLUID INCREASED. To what extent? well, buoyancy is directly related to density, and the buoyant force multiplied by greater than 2 but less than 2.5 to give you 12N. Therefore, the same thing should be expected for the DENSITY. Since SG is a comparison between DENSITIES, if the density of the fluid multiplied by x2-x2.5, then the SG should have done the same.

And presto, you take 0.7 and multiply by 2, but keep it less than what it would be if you multiplied by 3. you get somewhere in between 1.4 and 2.1.

2.1 is obviously too big (if you multiplied by 3). 1.7 is right in there at the perfect range.

This question took me 10 seconds to figure out. But only because I understood what had happened at the AAMC4 question with SG. Otherwise, I can understand how people would spend nearly 5 minutes on this single question.

THE KEY THING to realize in PS of MCAT is RELATIVITY.
This is the most important thing MCAT seems to emphasize in many problems that seem like a lot of work...

Hope that was of help.

SS3

 

[G1SG2]

An object that is totally immersed in benzene (specific gravity = 0.7) is subject to a buoyancy force of 5 N. When the same object is totally immersed in an unknown liquid, the buoyancy force is 12 N. What is the approximate specific gravity of the unknown liquid?

The answer is 1.7. Which formula did you guys use? I'm curious to see how people went about this one. I tried to manipulate a couple formulas but didn't see the relationship. I suck at liquids.

Okay, we know the buoyant force in benzene was 5N. Buoyant force Fb=pvg, where p=density of the fluid, v is the volume of the displaced fluid, and g is the acceleration constant. I'm just going to use 0.7 instead of the actualy density 700, since we want specific gravity in the end anyway (which will require us to divide by 1000 kg/m^3, the density of water).

So, Fb=pvg, 5=(0.7)(v)(10), 5/7=v, which is about 0.7. So, the volume of the displaced fluid is 0.7.

The new buoyant force is unknown liquid is 12 N. The object is going to displace the same amount of volume as it did in the other liquid, which is equal to it's own volume (Archimedes principle). So, 12=pvg, 12=p(0.7)(10), 12/7=p, p<2, which makes 1.7 the best answer. The key to this problem is to realize the missing element is the volume of the displaced fluid, which is the SAME in both liquids because an object will always displace it's own volume in any liquid. Hope this helps.

 

[puravida85]

Supersay.., thanks for the conceptual portion and I will check out the same problem in CBT4 and hopefully I get it right the next time.


Pookiez88, I know where I went wrong from seeing how you solved it. Instead of multiplying the (.7)x(10), I just crossed out gravity (10) for some reason. So I ended up having to divide (5)/(.7) instead. So my volume of displaced fluid was ~7. Putting that back into the the Force of 12 gave me effed up results. Thanks I really appreciate your explanation.

 

[jikuty]

I was really surprised that we needed to know what nearsightedness was for the PS section. I wouldn't expect them to test something like that.

 

[Hemichordate]

Q #41

When a strip of Cu is placed in H2O, no change is observed. However, when a Cu strip is placed into a solution of HNO3, a gas evolves. What is the most likely identity of the gas?

a) NO
b)CO2
c)H2
d) O3

I chose C, but the correct answer was A. I see why A works, but why doesn't C also work?

 

[G1SG2]

Q #41

When a strip of Cu is placed in H2O, no change is observed. However, when a Cu strip is placed into a solution of HNO3, a gas evolves. What is the most likely identity of the gas?

a) NO
b)CO2
c)H2
d) O3

I chose C, but the correct answer was A. I see why A works, but why doesn't C also work?

I think it's because the N would be more likely to be reduced as opposed to H.

 

[kabtq9s]

please explain how they found out that Cu will be oxidized and HNO3 will be reduced .. and how will this help us find the right answer.

thanks

 

[ratatat]

please explain how they found out that Cu will be oxidized and HNO3 will be reduced .. and how will this help us find the right answer.

thanks

Man I got that wrong too...H2 made so much sense. But I think their reasoning is that in the first attempted reaction (Cu with H2O), since Cu has a higher standard reduction potential, it wouldn't displace H2 and form CuO, so no H2 is evolved.

However, with Cu and HNO3, N is more electronegative so it would (I'm assuming) have a higher reduction potential. For instance, if you look at an abbreviated list of standard reduction potentials, the highest potential is F2. Cl follows it, then Br, then I. I think if N were included it'd be 2nd on that list. Thus, N wants to gain electrons and lower its oxidation number. In HNO3, H is +1, each of the three O atoms is -2, so N is +5. It wants to get reduced because it is electronegative/has a higher reduction potential. Therefore, it gets evolved.

The MCAT can be annoying eh? 😛

 

[kabtq9s]

I don't understand why I & II are incorrect ?

please comment

http://mysowar.wordpress.com/files/2009/08/aamc5-142.jpg

thanks in advance

 

[ezsanche]

yeah i got this one wrong. I thought it was 1 and 3

 

[Omni]

I thought it was I and II as well.
What'd you guys think about this practice test? I slumped down by 5 points from waht I usually score on this practice test :-\

 

[thebillsfan]

i slumped 7 pts. i wasnt really trying, but still 7 points is a lot to go down. a lot of people have that same experience, dont worry.

 

[planktonelement]

I slumped as well. Got a 32 on this one... then went up to a 41 on AAMC 6 (is 6 known for being easier?).

 

[Doodl3s]

i took the AAMC 5 in between 6 and 7, 6/5/7, and i got 42/36/42 lol
so yea, i did well, But i definitely took a hit on 5, mostly because of the science sections.

as far as that question everyone is asking about, the answer explains it well, in the beginning of the paragraph they talk about how it was infectious, so its DEFINITELY III... but the problem stated was that they couldn't find anything, so I is false. II is false because it is stated that it could not be grown AND because its the opposite of what a microbial pathogen should do

 

[doremi2010]

I don't really understand how to do number 27.

A particle is moving on a circular path, whose radius is 4cm, with a frequency of 4Hz. How long will it take for the particle to move through a distance of 16pi cm along the circle.

Do you use ang freq=2pi(freq) and so it's equal to 8pi rad/sec? But then to move a distance of 16pi wouldn't it be 2 sec?

 

[Omni]

This is how I did it:
The radius is 4cm, so the circumfrence is 8pi. Since its frequency is 4hz, then that means that it makes 4 revolutions in one second, in other words, 32pi cm in one second. So to move 16pi cm, it will take 0.5 seconds.

 

[wait4me]

ok i see that a lot of people are posting this question but i still dont get how to solve it?? what are the steps to go about getting the answer:

"When a strip of Cu is placed into H2O no change is observed. When it is placed into HNO3 a gas evolves. What is the identity of this gas?" Ans: NO

Cu+ HNO3---->
How do you know what the products are? I dont get how they got NO from HNO3?

 

[FlowRate]

LOL nevermind.. sometimes I want to slap myself for being silly.

For some reason, I was thinking
"more acidic = more pH = high pH"

DURRRR

 

[DKeyes247]

Hey Guys,

I used the print screen function on my computer to copy the AAMC question. Then I used the Paint program to cut out just the question. Now, I can't paste the question onto my message. Am I missing a step here?

Thanks!

P.S. Taking da Sept 4 MCAT!

 

[Evergrey]

Hey Guys,

I used the print screen function on my computer to copy the AAMC question. Then I used the Paint program to cut out just the question. Now, I can't paste the question onto my message. Am I missing a step here?

Thanks!

P.S. Taking da Sept 4 MCAT!

You'll need to host the picture on the web, and then link to it. Use photobucket or something similar for free image linking.

Btw, does anyone know what "photochemically reversible" means? This was in the Ozone passage of the PS section, I had no idea what it meant.

 

[Greenbayslacker]

.

 

[Greenbayslacker]

.

 

[Dr Yiot]

holy calculations on the PS section batman. Bio wasn't all that bad though...

 

[lDanny]

grr... #130. isn't longevity the same as long life span?

 

[lDanny]

grr... #130. isn't longevity the same as long life span?

 

[supras2kracer]

The way I thought of it was:

I asked myself what actually affects evolution of a species. A taxonomy depends on that because the goal is to have a lot of different classes and species (so diversity). Does a really long life span have anything to do with that? It's implied that they live long enough to reproduce so the length of the lifespan doesn't really matter.

I don't know what longevity means though, but hopefully this explanation helps!

 

[bluefish9810]

BS Q5: Most viral proteins are produced directly by:

I narrowed it down to:

A). Translation of host nucleic acid
B). Translation of viral nucleic acid

Answer is B., but I choose A because of the word "directly". The only way to produce viral proteins is by: 1). inserting viral DNA into host DNA 2). Transcription 3). Translation.

Am I not correct? Viruses cannot produce their own proteins because they have no such organelles, the only way to do so is by inserting their own DNA (or DNA from RNA with reverse transcriptase), so the correct answer should be A. Why did they choose B?

 

[LaurenMCAT]

Most viral proteins are produced directly by:

I narrowed it down to:

A). Translation of host nucleic acid
B). Translation of viral nucleic acid

Answer is B., but I choose A because of the word "directly". The only way to produce viral proteins is by: 1). inserting viral DNA into host DNA 2). Transcription 3). Translation.

Am I not correct? Viruses cannot produce their own proteins because they have no such organelles, the only way to do so is by inserting their own DNA (or DNA from RNA with reverse transcriptase), so the correct answer should be A. Why did they choose B?

The term "viral protein" indicates that the protein was encoded by the virus. Nucleic acid in this case refers to DNA. Like you recognized, the virus does have its own DNA, but not the machinery to do much of anything with it. 👍 So...its the virus DNA that's transcribed and translated using host machinery to make viral proteins. That matches with answer choice B! Woo hoo! 😀

 

[MilkIsGood]

ahaha just took aamc 5. missed 5 out of 7 ques on the picasso passage. love picasso..

 

[emericana]

This question just does not make sense to me. I was wondering if someone could help me understand why Zn(NO3)2 dissociates into 3 ions and why AgNO3 dissociates into 2.

Where do the 3 and 2 come from? How do I know that Zn has 3 and Ag has 2?

 

[Nabongo Mumia]

Zn(NO3)2 dissociates into one Zn2+ and two NO3- so total # of ions =
Ag(NO3) dissociates into one Ag and one NO3- so total # of ions = 2

So since the question was indirectly testing colligative properties, the one that dissociates into more ions wins! Hope this helps!

 

[emericana]

Zn(NO3)2 dissociates into one Zn2+ and two NO3- so total # of ions =
Ag(NO3) dissociates into one Ag and one NO3- so total # of ions = 2

So since the question was indirectly testing colligative properties, the one that dissociates into more ions wins! Hope this helps!

thanks so much! appreciate it!

 

[justhanging]

http://i22.photobucket.com/albums/b332/LosPepes/untitled.jpg

Did anyone else have a problem with PS # 42?
The question about the hill and a person on top of a 20m hill throwing a rock horizontally at 25m/s.


maybe am over thinking it but while I was doing it in the exam the 'assuming it can fall 20 m' was really bothering me. I don't think that because the answer is 50m it justifies the assumption made of it falling the 20 meters because the time used to calculate the 50 meters might be overestimated. Can someone clarify or atleast tell me that I only have 1minute per question so I don't waste my time over analyzing?

 

[kabtq9s]

http://i22.photobucket.com/albums/b332/LosPepes/untitled.jpg

Did anyone else have a problem with PS # 42?
The question about the hill and a person on top of a 20m hill throwing a rock horizontally at 25m/s.


maybe am over thinking it but while I was doing it in the exam the 'assuming it can fall 20 m' was really bothering me. I don't think that because the answer is 50m it justifies the assumption made of it falling the 20 meters because the time used to calculate the 50 meters might be overestimated. Can someone clarify or atleast tell me that I only have 1minute per question so I don't waste my time over analyzing?

I don't know how to explain it. But as soon as I read that problem I realized they were looking for distance so I remembered d=vt .. and since we don't have t I had to use another formula (that I memorized previously along with a list of all projectile motion equations) to figure it out. And it was all plug and chug from there on.

 

[SavBJJ]

Three weeks til June 16th test, taken AAMC 3 and 4, and Somehow i managed to get my best score yet on this exam and i was so ready to punch my monitor during the whole thing that it was hard to keep going. Soooo many ambiguous questions or questions with seemingly multiple right answers.

The worst was the schema VR passage by far for me. The only other one im adamant about being a ****ty question was the last one on the viral pathogen passage that somebody already mentioned. Why, if THEY DID EVENTUALLY SEE THEM IN THE SAME SAMPLES (with a better microscope) is I not correct? And Id say that not being able to culture the virions in media makes growing it "difficult", what exactly is their logic here?

Still im encouraged by guessing right answers for a better score but the BS and VR in this test blew. Hopefully later tests arent like this.

http://mysowar.files.wordpress.com/2009/08/aamc5-142.jpg

 

[JoAyi]

I don't understand why the answer is A? the explanation says that it has to be opposite direction to make the standing wave....
I am not following.....
Can anyone help? Thanks a lot.

For a given laser-cavity mode, the standing-wave pattern within a laser cavity can be viewed as a
superposition of two traveling waves. Their amplitudes and directions are described by which of the
following?
A) Equal amplitudes; opposite directions
B) Equal amplitudes; same direction
C) Different amplitudes; same direction
D) Different amplitudes; opposite directions