AAMC CBT4 and 4R OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT4 and 4R.

Please post ONLY questions pertaining to AAMC CBT4 and 4R.
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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[ofoshoukno]

the formula in the answer they give is E= (V-IR)/L

How the hell did they derive that formula?

 

[cornpops21]

Does anyone know the answer to the last question of the hematopoietic stem cell passage?

My princeton solutions don't even have it listed as a problem.

EDIT: Also, the last question on the passage about endothelium response to ACh.

God, I hate princeton.

By the way, i'm talking about the 4R version, not the CBT.

 

[amar21]

From the definition of the electric field: E = V/L. The -IR is taking into account the internal resistance of the battery, I dont think this is needed to solve the question tho.

the formula for electric field is given in in the passage

I just did this, got a 10/10/8... The bio passage on freezing/glucose kicked my ASS.. i got 4 of questions (of 5 i think) wrong... YEEEEEESH.

 

[amar21]

I get that Fa=-Fb... its newtons third law.. yadda yadda... and I had chosen that, but I made it 2F for this reason

If the force of one collision caues the other to accelerate, isnt Fnet=ma? in which mass must come into play...

any insight?

 

[amar21]

Right, but the answer seems to have current flowing in the other direction...Kinda hard to explain the whole question but if anyone has the test and knows what I'm talking about, that'd help...thanks though

ditto.. i thought current went + ----> -... but the explanation says its the other way around

I still don't get how they figurd out the other resistor in parallel had 1A flowing through it..

 

[GoldShadow]

For question 50 in the Physical Sciences section regarding circuits, how come the answer shows the voltage moving in the opposite direction? Does it normally flow out of the "bigger side" of the voltage source? Like l| --> vs. |l --> (if that makes any sense)?

ditto.. i thought current went + ----> -... but the explanation says its the other way around

I still don't get how they figurd out the other resistor in parallel had 1A flowing through it..

I think you misunderstood what it was saying; it never said the current flowed in the opposite direction. They meant that once you figured out how much current was going through each individual parallel resistor, you would know how much total current was flowing through any other point in the circuit. The current would go through the parallel resistors, around, through the voltage source and 13-ohm resistor, then go to the 3-ohm resistor. They didn't mean it flowed directly from the parallel resistors straight to the 3-ohm.

Also, you can figure out how much current is in parallel resistors because the voltage drop across any resistors in parallel is the same. In other words, V of the 2-ohm resistor = V of the 4-ohm resistor.
By Ohm's Law, V=IR, you can set the two voltages equal to one another:

V1=V2, or IR=IR.

You know both resistances and the current flowing through one of them.

(2 ohm)(2 amp)=(4 ohm)I
Solve for I, and you get I=1 amp.

Since current is split up when the circuit splits up, all of it combines once the circuit converges again. So at any point along the circuit that is not split (ie, that is in series), the current will equal 2 amp + 1 amp = 3 amp.

 

[sezratd]

Does anyone has the answer to AAMC #4? Mine was confusing and out of order. If somebody has it, let me know.

 

[futuredoctor10]

.Question 121, CBT..

I thought you could add neurons at "I" - if that is where you feel the painful stimulus, couldn't you place ADDITIONAL NEURONS there? [I didn't follow their explanation for why I is not valid]
.

 

[addy100]

u also could hv used d molarity, but it would hv been a longer calculation. number of moles= molarity x volume. then multiply ur answer by 101.1, d molecular weight. This would hv also given u 22.65. u just hv 2 b careful with estimation with this problem, as 22.41 is close 2 d answer..

 

[Homoochan]

The solubility data indicate that Compound C most likely contain which of the following functional groups?

The explanation says amide and nitro containing compounds are not soluble in dilute acid and base. Anybody know why? If it were strong acid and base would it make a difference?

carboxylic acid is soluble in dilute base because it becomes COO- right? Why does it have to be "dilute" base? not strong base?

Thanks!

 

[travelingdoc]

can anyone pm these to me pleaseeeeeeeeeeee?

 

[Lukkie]

Does anyone has the answer to AAMC #4? Mine was confusing and out of order. If somebody has it, let me know.

can anyone pm these to me pleaseeeeeeeeeeee?

just buy the damn tests like you are supposed to.

 

[Homoochan]

The solubility data indicate that Compound C most likely contain which of the following functional groups?

The explanation says amide and nitro containing compounds are not soluble in dilute acid and base. Anybody know why? If it were strong acid and base would it make a difference?

carboxylic acid is soluble in dilute base because it becomes COO- right? Why does it have to be "dilute" base? not strong base?

Thanks!

no one knows?

 

[andafoo]

For question 153 in the Biology Section:

The mention that compound C is soluble in both dilute acid and base... how does that indicate that it has both a acidic and basic group on it?

 

[Lukkie]

For question 153 in the Biology Section:

The mention that compound C is soluble in both dilute acid and base... how does that indicate that it has both a acidic and basic group on it?

yes

 

[andafoo]

yes

mind explaining?

 

[andafoo]

Another question I had was #173:

I knew that totipotent stem cells were required, but what in the question indicated that the deterministic theory was the rationale. The main goal was to replace ALL types, so hormonal signals wouldn't be that important no? Anyone have a good explanation for why D is correct and why C is incorrect?

 

[andafoo]

double bump, (see both questions)

 

[Lukkie]

mind explaining?

for the mcat and most basic problems, something is soluble in water only if its very polar, ie carries a charge. if something is soluble in dilute base, it should be acidic so it can give up a proton, to make the solute negatively charged. on the other hand, a base like a tertiary ammonia group is soluble in dilute acid since it can accept a proton and get a positive charge

 

[Lukkie]

double bump, (see both questions)

Another question I had was #173:

I knew that totipotent stem cells were required, but what in the question indicated that the deterministic theory was the rationale. The main goal was to replace ALL types, so hormonal signals wouldn't be that important no? Anyone have a good explanation for why D is correct and why C is incorrect?

how did you access this question. the tests i purchased on e-mcat.com only go up to problem #146.

 

[banister]

how did you access this question. the tests i purchased on e-mcat.com only go up to problem #146.

He has the AAMC 4R which is the paper based one (older, longer) that contains many of the same passages.

 

[Deepa100]

.Question 121, CBT..

I thought you could add neurons at "I" - if that is where you feel the painful stimulus, couldn't you place ADDITIONAL NEURONS there? [I didn't follow their explanation for why I is not valid]
.

Pain stimulus goes all the way up to the brain. The afferent pain fiber synapses on the afferent fibers on the spinal cord. These travel up to the pain centers in brain. Since this path does not come back to the muscle, I thought the answer would be A. Does any one have a better explanation?

 

[basedonkoh]

could someone please explain in detail why a different second base would be used in the second alkylation of acetoacetic ester?

THANKS!

 

[koogles]

bump
anyone understand why for #121 I is incorrect? I'm not really following even with the explanations above

 

[TooMuchResearch]

bump
anyone understand why for #121 I is incorrect? I'm not really following even with the explanations above

Because IV is incorrect, and the only choice including I also includes IV. Alternatively, I think it is because the neuron shown between I and II is the sensory/afferent neuron, and the additional neurons (interneurons?) required to send the signal to the brain don't originate from the same place as the sensory neuron. Hmm, I think the neuron from I to II goes from the foot (or toe) to the spine. From point II, an additional neuron could carry the signal to the brain which would return the signal at III.

 

[TooMuchResearch]

This test represents somewhere around the 10th Hardy-Weinberg question I have gotten wrong on practice tests, so I finally looked up how to use it. I feel much smarter now

 

[Yope]

Why is this decay positron emission instead of electron capture? Because the passage makes no explicit mention of electrons in the decay process? I got the question right without really thinking about it, but upon further review, I've now confused myself.

 

[GoldShadow]

The question asks what kind of particle is emitted in the decay of Potassium-40 to Argon-40. Besides the fact that electron capture is not an answer choice (since something is being emitted, not captured), the only answer choice that fits is positron.

 

[Yope]

The question asks what kind of particle is emitted in the decay of Potassium-40 to Argon-40. Besides the fact that electron capture is not an answer choice (since something is being emitted, not captured), the only answer choice that fits is positron.

What confuses me is that, in electron capture, a proton merges with an electron to form a neutron. The mass stays the same, the atomic number decreases by one, and a gamma ray is emitted.

Choice D makes a lot of sense, but I don't know why Choice A is wrong.

 

[moldovanits]

How many grams KNO3 are in 100 mL of the student-prepared solution of KNO3(aq)? A
) 11.33 g B
) 22.41 g C
) 22.65 g
From Table 1, there is 226.5 g KNO3, the solute, per liter of solution. In 100 mL, there is one-tenth the mass, or 22.65 g. Thus, answer choice C is the best answer.

D
) 34.00 g


this should be simple but can someone please explain it to me. i took chem along time ago.

 

[iA-MD2013]

Moving to Study question Q&A subforum.

 

[yousafob]

How many grams KNO3 are in 100 mL of the student-prepared solution of KNO3(aq)? A
) 11.33 g B
) 22.41 g C
) 22.65 g
From Table 1, there is 226.5 g KNO3, the solute, per liter of solution. In 100 mL, there is one-tenth the mass, or 22.65 g. Thus, answer choice C is the best answer.

D
) 34.00 g


this should be simple but can someone please explain it to me. i took chem along time ago.

(226.5 g KNO3/ L) x (0.1 L) = 22.65 g

Make sure your units cancel to give you the correct answer in grams.

 

[moldovanits]

(226.5 g KNO3/ L) x (0.1 L) = 22.65 g

Make sure your units cancel to give you the correct answer in grams.

thank you sir!

 

[Vihsadas]

Please remember only to post questions from the official AAMC exams in the official thread created for each specific AAMC exam. If one of your peers should accidentally click on this thread, they may see a spoiler for this question, ruining its testability. This policy is outlined in the stickies above here:

http://forums.studentdoctor.net/showthread.php?t=516243

I will merge this thread with the offical thread for AAMC test 4 now. Thanks!

 

[YellowDiamond]

Just took AAMC 4 and am going through the answers. One question I didn't particularly like was the discrete talking about how gas movement occurs in the lungs. I wanted to avoid the word "pumping" at all costs as in mammalian systems the air simply moves by pressure differentials; I thought pumping was very misleading. I chose diffusion based on the pressure differene. Just wondered what you guys thought.

 

[Zona Pellucida]

Just took AAMC 4 and am going through the answers. One question I didn't particularly like was the discrete talking about how gas movement occurs in the lungs. I wanted to avoid the word "pumping" at all costs as in mammalian systems the air simply moves by pressure differentials; I thought pumping was very misleading. I chose diffusion based on the pressure differene. Just wondered what you guys thought.

I did the same thing and also got this one wrong. LAME

 

[Dr Gerrard]

Just took this. 12/11/11.

What was up with that one passage, on 4R, about the endothelium? Was that hard or was it just me? I missed 5 of those questions, which would have put me at a solid 12.

 

[golfyfan]

Can anyone tell me why the answer from #35 of PS is not D? I get how A could potentially be correct if KHP didn't have an aq subscript. It's the question from passage 5 of 4R, about determining unknown acids by neutralization with NaOH.

Also for #53 (independent question) with the capacitors and use of square wave signal, I put my answer as D but the real answer is A. The explanation that was given was because the capacitor then discharges. But how were we suppose to know that there is a discharge? The question never mentions the voltage will be turned off.

 

[manutdfan]

nevermind, got it

 

[capn jazz]

Okay, I need some help with PS #42:

An electron is ejected from a cathode by a photon with energy slightly greater than the work function..... compare final KE of electron at the anode to its intial PE after ejection

My reasoning was:
Kinetic Energy of the electron will be photon energy minus work function = a very small amount => so photon energy was a little higher than 2x10^-19
Potential energy = qV = (1.6x10^-19)(50V) = 8x10^-18

After the work function is removed from the photon's energy, won't the photon KE be reduced greatly, so that it's less than the PE?

I don't get their explanation for why they're equal. Help!

 

[Yoyomama88]

the reason why the PE and KE are equal is simply because the INITIAL KE of the ejected electron is Very Small. This was defined by KE = Photon E- Work Function.


The the ejected Electron thus has 99 percent PE in the beginning, which all transfers to KE by the time the electron leaves the (-) cathode and hits the (+) anode. So the KE final is equal to the tiny KE initial plus all the KE gained from the initial PE.

 

[brushbordermb]

*What does 20% wt/wt mean?

What is the difference between molarity and solute concentration?

The question asked, how many grams KNO3 are in 100 mL of the student prepared solution of KNO3 (aq)?
A-11.33 g
B-22.41 g
C-22.65
D-34.00
I used the molarity and got B. However, the answer is C. The way I did this question was to find the MM of KNO3, multiply by mol/L, multiply by Volume (g/mol x mol/ L x 100 mL x L/1000 mL). Please explain me the problem with my reasoning.
​

How do you determine if the gas is flammable?

Suppose a certain far-sighted person can see object clearly no closer than 300 cm away. What is the minimum distance from a plane mirror such a person must be to see his reflection clearly? Answer is 150 cm. I don't know what formula they used, or what concepts are being tested from lenses.

Thanks for your help.

 

[brushbordermb]

bump! anyone???

 

[G1SG2]

*What does 20% wt/wt mean?

What is the difference between molarity and solute concentration?

The question asked, how many grams KNO3 are in 100 mL of the student prepared solution of KNO3 (aq)?
A-11.33 g
B-22.41 g
C-22.65
D-34.00
I used the molarity and got B. However, the answer is C. The way I did this question was to find the MM of KNO3, multiply by mol/L, multiply by Volume (g/mol x mol/ L x 100 mL x L/1000 mL). Please explain me the problem with my reasoning.
​

How do you determine if the gas is flammable?

Suppose a certain far-sighted person can see object clearly no closer than 300 cm away. What is the minimum distance from a plane mirror such a person must be to see his reflection clearly? Answer is 150 cm. I don't know what formula they used, or what concepts are being tested from lenses.

Thanks for your help.

Can you post the equation for the KNO3? Not sure if I can help you without it.

For a plane mirror-the distance from the object to the mirror=distance from mirror to the image. So, in the problem:

Person----mirror-----image (300cm from person-this is what you're given in the question). Since the do=di:

Person----mirror is 150 cm. Mirror-----image is 150cm. 150+150=300 cm.

 

[brushbordermb]

Attached is the image for that question. Thanks for your help.

 

[G1SG2]

Attached is the image for that question. Thanks for your help.

The question is asking for grams of KNO3. You're given a certain volume, 100 mL. In the table, you have the solute conc. 226.5 g/L. This is perfect, because g/L * L=g, which is what we're looking for. Sometimes, dimensional analysis can really make a problem simple.

226.5 g/L * 100 x 10^-3 L=22.65 g. You could've also used molarity, but why would you do that? Molarity=mol/L. Solute conc.=g/L. You already have what you need. You could've used molarity but you'd have to convert to grams first. M=2.241 mol/L * 101 g KNO3 /1mol KNO3=226 g/L-you would've ended up with the solute concentration if you used molarity anyway. I think you messed up the calculations. Don't use a longer method if you're already given what you need. And, the difference between solute conc. and molarity is that solute conc. is expressed in grams, whereas molarity uses moles. Hope this helps.

 

[brushbordermb]

The question is asking for grams of KNO3. You're given a certain volume, 100 mL. In the table, you have the solute conc. 226.5 g/L. This is perfect, because g/L * L=g, which is what we're looking for. Sometimes, dimensional analysis can really make a problem simple.

226.5 g/L * 100 x 10^-3 L=22.65 g. You could've also used molarity, but why would you do that? Molarity=mol/L. Solute conc.=g/L. You already have what you need. You could've used molarity but you'd have to convert to grams first. M=2.241 mol/L * 101 g KNO3 /1mol KNO3=226 g/L-you would've ended up with the solute concentration if you used molarity anyway. I think you messed up the calculations. Don't use a longer method if you're already given what you need. And, the difference between solute conc. and molarity is that solute conc. is expressed in grams, whereas molarity uses moles. Hope this helps.

Thanks.

 

[jikuty]

Can someone please explain to me the logic behind Question #140 in the Biological Sciences section? It reads "Why is a different base often used for a second alkylation of acetoacetic ester?".

I answered B. I figured that once you have another alkyl group near the acidic hydrogen, the corresponding anion after removal of the hydrogen would be more stabilized (since the negative charge would have more space to disperse itself). By this logic, I thought that the monoalkylated acetoacetic ester would be more acidic than the non-alkylated one.

The correct answer is A, which states that the monoakylated ester is less acidic than the non-alkylated one. Can anyone help me out?

 

[vandyam]

yes, please. I happened to guess this one right, but I'm very weak on orgo so any help would be appreciated.

 

[jikuty]

... bump.

Can anyone help us out with that organic question? (Thanks!)