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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[radiohead55]

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[engineeredout]

Appologies in advance for this question, but I know I am missing something:

I thought transparent meant that it allowed light to pass through. The question stem says the best scintillators are nearly transparent to the wavelengths of light that they emit. The answer makes sense, but how could I have figured this out based on the passage information?

Thanks in advance!

Post the full question.

 

[osuguy]

for ps #45
i guess i dont really understand what the question is asking. Does it mean that the two waves are coming from opposite directions because the mirror reflects it back with the same amplitude but opposite direction?

The explanation isnt really the best either. I was hoping someone had a better explanation or did i just make it harder than it appeared

Thanks!

 

[engineeredout]

for ps #45
i guess i dont really understand what the question is asking. Does it mean that the two waves are coming from opposite directions because the mirror reflects it back with the same amplitude but opposite direction?

The explanation isnt really the best either. I was hoping someone had a better explanation or did i just make it harder than it appeared

Thanks!

Look at the diagram. At any given point they have the same amplitude with opposite sign.

 

[Lukkie]

can someone help me with PS 43? it is the sled question. how does the speed of the sled rider change if he starts at 10m instead of 20m height.

my setup is this:
mgh=mv^2/2
2gh=v^2
v=sqrt(2gh)

so v, when h=20, is 20. [sqrt(400)]
when h=10, v= 10*sqrt(2) [sqrt(200)]

so i guessed choice B, slower by factor of 2*sqrt(2). however, the answer is D, slower by only sqrt(2).

what am i doing wrong? i understand their answer, but dont conceptually understand why my solution leads to the wrong answer.

 

[mastamind518]

can someone help me with PS 43? it is the sled question. how does the speed of the sled rider change if he starts at 10m instead of 20m height.

my setup is this:
mgh=mv^2/2
2gh=v^2
v=sqrt(2gh)

so v, when h=20, is 20. [sqrt(400)]
when h=10, v= 10*sqrt(2) [sqrt(200)]

so i guessed choice B, slower by factor of 2*sqrt(2). however, the answer is D, slower by only sqrt(2).

what am i doing wrong? i understand their answer, but dont conceptually understand why my solution leads to the wrong answer.

v^2 = 2gh

when h=10, v^2 = 2g(10)
when h = 20, v^2 = 2g(20)
the '2g' cancel out, leaving v=rad10 and v=rad20
(rad10)(rad2) = rad20
therefore, when the speed when the height is 10 needs to be increased by rad2 to equal the speed when the height is 20.

 

[spyderracing32]

In response to the sled:

Set up the equations as a fraction:

(1/2)mv_1^2 = mgh
__________________
(1/2)mv_2^2 = mg2h


Cancel like terms and get:

v_1^2 = 1
_________
v_2^2 = 2

Take the sqrt of both sides and you get:
v_1 = 1
_______
v_2 = 2^.5

 

[spyderracing32]

Phys Sciences (CBT Question 6)
From rxns 3-5, what can be determined about the relative concentrations of CFCs and O2?
Answer: (C) A catalytic amount of CFC can produce much O2.

This question has been posted earlier as well. I understand that the Cl radical is not consumed in the reaction and is reformed, similarly for the ClO radical.

What I don't understand: the CFC in the passage is defined as CF3Cl. When I read this question, I assumed that CF3Cl got "altered" in the reaction - because it was broken down into a CF3 radical and Cl radical. Since catalysts are not altered or consumed in a reaction, I assumed this choice (C) could not be correct.

The answer I picked was (B) - 1 equivalent of CFC is required to produce 2 equivalents of O2. Can someone explain why this is wrong?
** I eliminated A and D so had I known this was wrong, I would have picked C.

Thanks! Anyone who understood this question please reply!!!!!!!!

A catalytic amount just means a very small amount. The other answers are obviously wrong because as the Cl radical is formed it sets off a chain reaction, so 1 equivalent of CFC makes much more than just 2 equivalents of O2. The purpose of the CFC is just to provide the Cl free radical that is regenerated in reaction 5. Given that the reactions take place in an O3 rich atmosphere the Cl radical that is regenerated will simply continue to react in a cyclic manner.

They never claim the CFC is a catalyst, just that a catalytic amount is added (an amount that will start the reaction that would otherwise not occur). As a general rule, catalytic amount = small amount.

 

[spyderracing32]

Wow, I knew I was going to kick myself when someone explained it to me! I completely missed the 60 N friction force value given in the passage...Oh dear. Thanks so much!

You should understand that the force due to friction is the coefficient of kinetic friction times the normal force, and the normal force on an incline = (m)(g)cos(theta), where theta = the angle between the incline and the ground.

 

[futuredoctor10]

They never claim the CFC is a catalyst, just that a catalytic amount is added (an amount that will start the reaction that would otherwise not occur). As a general rule, catalytic amount = small amount.

Oh ok that makes sense, got it! thanks!

 

[lixxx669]

#118
Isn't a compond with -(CO)-NH- classified as amide (like the one in protein)? why the answer shows its imide (in my knowledge, imide shoud look like -R=N-)

I attatched a pic of this question.

 

[lixxx669]

#118
Isn't a compond with -(CO)-NH- classified as amide (like the one in protein)? why the answer shows its imide (in my knowledge, imide shoud look like -R=N-)

I attatched a pic of this question.

 

[futuredoctor10]

lixxx - I didn't get this right either.

"An imide is a functional group consisting of two carbonyl groups bound to a primary amine or ammonia."

Imide: http://en.wikipedia.org/wiki/Image:Imide.png
Amide: http://en.wikipedia.org/wiki/Image:Amide-general.png

Hope that helps

 

[lixxx669]

Thanks, I thought it was Imine instead of Imide

 

[Lukkie]

Thanks, I thought it was Imine instead of Imide

imine is C=N

 

[wrathofgod64]

did anyone else get completely destroyed by the verbal on this section? This was by far my lowest verbal score...

 

[Lukkie]

did anyone else get completely destroyed by the verbal on this section? This was by far my lowest verbal score...

yeah.... got an 8 when i took it through the Full Length. when i did the VR section by itself 1.5 weeks later, I got a 9. probably the hardest VR section ive taken.

 

[JaggerPlate]

This test reallly sucked for me. I missed the cut off for one point higher by ONE question on each section. No joke, I was one question off from a higher score in each section. I was having computer problems and ended up taking this test later in the day and under rushed conditions. It really discouraged me ... thinking about not taking the test in a few weeks or taking it but voiding or planning on a retake.

 

[TooMuchResearch]

CBT Item 108:

An extra S phase occurs during amitotic division in a small macronucleus to minimize the fluctuations in DNA content. This is most likely triggered by the presence of:

A) low concentrations of DNA in the macronucleus.
B) centromere in the macronucleus.
C) high concentrations of DNA in the micronucleus.
D) mitotic enzymes in the micronucleus.

This is from the fairly nasty Tetrahymena passage others complained about. The AAMC explanation for why A is correct didn't make sense to me, so I'm hoping someone else may be able to explain it in better terms.

 

[Revilla]

CBT Item 108:

An extra S phase occurs during amitotic division in a small macronucleus to minimize the fluctuations in DNA content. This is most likely triggered by the presence of:

A) low concentrations of DNA in the macronucleus.
B) centromere in the macronucleus.
C) high concentrations of DNA in the micronucleus.
D) mitotic enzymes in the micronucleus.

This is from the fairly nasty Tetrahymena passage others complained about. The AAMC explanation for why A is correct didn't make sense to me, so I'm hoping someone else may be able to explain it in better terms.

The way I reasoned it out is by considering what happens during S phase -- DNA replication. The question stem says the reason for the additional S phase was to minimize fluctuations in DNA content and the passage says that during division, you end up with uneven nuclei, so I figured if they needed another S phase (another S phase = another round of replication), the DNA concentration from just one S phase must be too low.

And I hated that passage too.

 

[FutureScaresMe]

Q.9 if ocean waves strike the shore every 3.0 s and the horizontal distance between adjacent crests and troughs is 1.0 m, what is the average speed of the waves?

Anyone else agree the wording on this problem is absolutely ridiculous? You can infer from this description that the wavelength is either 1m or 2m...

 

[thatgirl413]

I have a question about 42 on the PS
...From ground level, a person at Point A throws a snowball horizontally to the right at 25 m/s. Where does the snowball land?

I understand that distance = velocity x time, and the velocity is 25 m/s. But why can't you use: Vf=Vi + at to find the time in flight?? Vf = 0 (since it land), Vi= 25, and a= -10 m/s^2? They used d=1/2at^2 to find time in flight, but i thought thats for free fall only...and here the person is throwing horizontally and not straight down. Thanks!

(the answer is 50 m, btw)

 

[marele86]

I have a question about 42 on the PS
...From ground level, a person at Point A throws a snowball horizontally to the right at 25 m/s. Where does the snowball land?

I understand that distance = velocity x time, and the velocity is 25 m/s. But why can't you use: Vf=Vi + at to find the time in flight?? Vf = 0 (since it land), Vi= 25, and a= -10 m/s^2? They used d=1/2at^2 to find time in flight, but i thought thats for free fall only...and here the person is throwing horizontally and not straight down. Thanks!

(the answer is 50 m, btw)

Because AAMC, in their infinite wisdom, wrote 'from ground level' when they MEANT from Point A (which you can see in the diagram is 20m HIGHER than ground level'. Therefore, their explanation (find the time from the y-axis equation, plug it into the x-axis equation to find distance) is correct.

The reason we can't use Vf=Vi + at to find the time in flight is because Vi=25 is for the x axis, as it states that the snowball is thrown 25 m/s to the right. And that's fine, but since there is no acceleration in the x direction (a=0), the second term drops out, and that includes t. No way to solve for it if it's multiplied by 0 in the equation.

Incidentally, the time required for an object to travel a given distance is independent of any x direction velocity given to it, and solely dependent on the value of g and the height (y-axis) it is dropped from.

And I get why they said 'from ground level' (the ball is thrown at 20m high, not 20m+height of person throwing it) but, jeez, they should've found a better way to phrase that!

 

[ohsmurfyea]

B/c the question says a new metal forms on the Cu strip I thought that Cu was gaining electrons so it would be reduced. How do we know that Cu is oxidized when it goes into the solution?

 

[DocDrakeRamoray]

B/c the question says a new metal forms on the Cu strip I thought that Cu was gaining electrons so it would be reduced. How do we know that Cu is oxidized when it goes into the solution?

Because Cu would rather get oxidized ( lose electrons and became Cu2+ ion) than get reduced.

 

[DocDrakeRamoray]

I personally think this test had quite a few tricky questions.

 

[rocketbooster]

#32 bio.

"Dissection of a crayfish reveals the presence of a hepatopancreas. Of which system below would one expect this organ to be a vital component?"

I narrowed it down to Circulatory and Digestive.

I went with circulatory. how can you choose between these two? the liver and pancreas aid in both the digestive and circulatory systems. for digestive, they release bile and digestive enzymes. for circulatory, the liver releases blood, amino acids, fatty acids, lipoproteins, etc. into the blood and the pancreas releases glucagon and insulin. how can you honestly eliminate circulatory? do they count those functions I listed as that of the endocrine system? I understand it's technically endocrine, but aren't those hormones transported through the blood, thus circulatory system?

their answer is "The term hepato- refers to the liver. Both the liver and the pancreas in vertebrates are associated with the digestive system. The liver empties bile and the pancreas empties digestive juices into the small intestine. The digestive system is the correct choice (D)"

anyone?

 

[VanBrown]

#32 bio.

"Dissection of a crayfish reveals the presence of a hepatopancreas. Of which system below would one expect this organ to be a vital component?"

I narrowed it down to Circulatory and Digestive.

I went with circulatory. how can you choose between these two? the liver and pancreas aid in both the digestive and circulatory systems. for digestive, they release bile and digestive enzymes. for circulatory, the liver releases blood, amino acids, fatty acids, lipoproteins, etc. into the blood and the pancreas releases glucagon and insulin. how can you honestly eliminate circulatory? do they count those functions I listed as that of the endocrine system? I understand it's technically endocrine, but aren't those hormones transported through the blood, thus circulatory system?

their answer is "The term hepato- refers to the liver. Both the liver and the pancreas in vertebrates are associated with the digestive system. The liver empties bile and the pancreas empties digestive juices into the small intestine. The digestive system is the correct choice (D)"

anyone?

you need to use the information in the passage to eliminate answer choices.

A) Circulatory system - The passage states that arthropods have an open circulatory system... therefore the vertebrate functions of a pancres/liver probably don't apply.

b) Excretory - Passage states that the malpighian tubes carry out this function.

c) Nervous - No way to correlate this.

d) Digestive - The passage states that arthropods have intestine... purely based off of elimination of other choice we arrive here but the passage explicitly stating the presence of an intestine and, thus, a digestive tract leads you to this BEST answer.

 

[Jhoa001]

The best material to use as scintillators are nearly transparent to the wavelengths of the light that they emit. This characteristic is important because:
A) it minimizes the reabsorption of light. (Correct)
B) it maximizes the reabsorption of light. (I picked this one)

I don't quite understand the reasoning behind this question. Wouldn't we want to maximize the absorption of light to the photomultiplier tube?

Thanks for the help!

 

[Zona Pellucida]

The best material to use as scintillators are nearly transparent to the wavelengths of the light that they emit. This characteristic is important because:
A) it minimizes the reabsorption of light. (Correct)
B) it maximizes the reabsorption of light. (I picked this one)

I don't quite understand the reasoning behind this question. Wouldn't we want to maximize the absorption of light to the photomultiplier tube?

Thanks for the help!

I also got this wrong using the same reasoning you used.

You don't want the scintillator to absorb light before it gets to the photomultiplier so you can get an accurate reading. I also picked "it maximizes the reabsorption of light" because I thought it meant it would maximize the reabsorption of light by the PHOTOMULTIPLIER. Apparently they were only concerned with the scintillator doing the absorbing which is why A was correct. Lame question, be more specific AAMC!

 

[rule out normal]

The answer explanation says that viruses cannot be cultured in media. Well, what if that media were comprised of host tissue cells? Or host bacteria? What exactly do they mean here?

 

[ronaldo23]

I know you use d=vt, and determine t from d=vot + 1/2at^2. But why is the initial velocity 0? It says that she throws the ball with a velcoity of 25 m/s...why can we assume its 0 velocity?

 

[Aggro]

I know you use d=vt, and determine t from d=vot + 1/2at^2. But why is the initial velocity 0? It says that she throws the ball with a velcoity of 25 m/s...why can we assume its 0 velocity?

X velocity and Y velocity are completely unrelated. The ball was thrown directly to the right, so initially, the velocity in the y-direction is 0 m/s.

Solve for t first, via d = 1/2at^2, then plug t into x = v*t to get the distance.

Also, just note that if you get a question where a ball is thrown with both x and y velocity, you need to separate the components first.

 

[G1SG2]

Passage III, number 16:

The 14C atom undergoes beta decay to 14N. What particle is being emitted from the carbon nucleus?

The answer: electron. Huh? Isn't that question poorly worded? Electrons are not in the nuclei! I know in beta decay, the atom gives off a negative charge, and increases its atomic number by 1 to compensate for the negative charge. I picked neutron, because I thought of the neutron becoming the proton for the +1 charge to compensate for the -1 charge produced by the electron being emitted from the atom. Does anyone else agree (about the question being poorly phrased)?

 

[G1SG2]

Bump!!

 

[dray5150]

Can somebody explain # 16 on Bio?

When an initial heterozygous macronucleus undergoes repeated binary fission the results are:

Its say D: a variable allelle distribution in the marcronucleus.


My reasoning was "variable allelle" was more than enough to eliminate this answer because we were dealing with binary fission. Can someone please explain?

And also number 25 in Bio: How to do you know to add heat?? I picked acidification but I'm not to sure why heat was the answer. Is that something you just have to know?


Also on the amine and anhydride passage: This passage slaughtered me. I missed like 4!! Anyways can someone help me with 25 and 26
On 25 how do you know to add heat to reverse this reaction...?? Is this something you should should just memorize or is it some how implied in the passage?
And on 26 I really didn't know if the carbonyl oxygen should have been protonated but I picked it and got it wrong. Is what makes it wrong being that the H on the NH2 doesn't ever protonate a carbonyl reaction like water would? Could some one please explain

 

[boaz]

On 25 how do you know to add heat to reverse this reaction...??

If you think about the transition state of the reaction you should notice that it is not stable. Since activation energy is high, heat is required. Whether or not the product is more stable is irrelevant; it's the Ea that matters.

And on 26 I really didn't know if the carbonyl oxygen should have been protonated but I picked it and got it wrong. Is what makes it wrong being that the H on the NH2 doesn't ever protonate a carbonyl reaction like water would? Could some one please explain

That was a trick. If you want to protonate the carbonyl carbon you'll instead get the nitrogen protonated and destroy it's nucleophilicity. The carbonyl carbon is electrophilic enough to be attacked by a good nucleophile like lone-pair nitrogen.

Hope that helps!

 

[dray5150]

Thanks so much.. it did!!!

 

[capn jazz]

Commenting to complain...

The sled passage! My brain stupidly equates a force of "50N" and a weight of 50 kg with each other due to the N reminding me of the normal force and the numbers being the same. So I got 1 for the coefficient of friction rather than .1.

Then, AAMC's STUPID wording on the snowball throwing question - from "ground level" at pt A. I tried for the longest time to figure out how to get the distance, and finally resorted to "well, it has shorter to fall to reach the ground than if they were at the top of the hill" and found the RIGHT answer (50 m) using the top of the hill and reasoned that it must be less than that. Dumb, dumb, dumb. Those two questions alone would have given me an 11 instead of a 10 on PS.

 

[G1SG2]

Passage III, number 16:

The 14C atom undergoes beta decay to 14N. What particle is being emitted from the carbon nucleus?

The answer: electron. Huh? Isn't that question poorly worded? Electrons are not in the nuclei! I know in beta decay, the atom gives off a negative charge, and increases its atomic number by 1 to compensate for the negative charge. I picked neutron, because I thought of the neutron becoming the proton for the +1 charge to compensate for the -1 charge produced by the electron being emitted from the atom. Does anyone else agree (about the question being poorly phrased)?

Anyone?

 

[capn jazz]

Whether the question is poorly worded or not isn't really relevant since it's a very common way of phrasing beta decay. You should think "beta decay" and immediately "electron emitted". Whether it's from the nucleus or not isn't really the point. If a neutron left, you would have 13N.

 

[capn jazz]

Can anyone explain why a diverging lens corrects near-sightedness?

 

[Fort]

Can anyone explain why a diverging lens corrects near-sightedness?

If you're near sighted, then you can't see far away. If light is entering an eye from very far away, then the rays will converge at a point behind the retina. In other words, the lens in the eye is too powerful, and they converge the light rays too much; however, if the rays are near, then they will converge at the retina just fine; hence, near sighted.

Now if we want to correct this we have to make the lens "less powerful", and to do that is to add a diverging lens in front of the already powerful converging lens in the eye. This causes the parallel rays to diverge just enough so that the image will be formed on the retina where it should be.

Hope that helps.

 

[Fort]

Passage III, number 16:

The 14C atom undergoes beta decay to 14N. What particle is being emitted from the carbon nucleus?

The answer: electron. Huh? Isn't that question poorly worded? Electrons are not in the nuclei! I know in beta decay, the atom gives off a negative charge, and increases its atomic number by 1 to compensate for the negative charge. I picked neutron, because I thought of the neutron becoming the proton for the +1 charge to compensate for the -1 charge produced by the electron being emitted from the atom. Does anyone else agree (about the question being poorly phrased)?

Beta decay only involves an electron or a positron. In this case, a beta particle with a negative charge is being emitted. The rest is just algebra book-keeping.

14/6C ---> 0/-1(Beta) + 14/7 N

The number of protons and neutrons on the left equals those on the right. So a beta particle is being emitted in the form of an electron.

 

[G1SG2]

I remember there was a question in the BS that goes something like this (I have it in my notes for when I reviewed the exam):

"If an artery that supplies blood to a lung lobe was blocked but ventilation to the lobe was unaffected, how would alveolar gas partial pressures change? PO2 would increase and PCO2 would decrease. If the blood flow to an alveolus were blocked there would be no flow of hemoglobin-rich red blood cells to take away O2 and no influx of CO2 from the blood. As a result the air in the alveolus would become more like that of the atmosphere. It would acquire a higher PO2 and a lower PCO2."

Is this question referring to the pulmonary artery?

 

[matth87]

I remember there was a question in the BS that goes something like this (I have it in my notes for when I reviewed the exam):

"If an artery that supplies blood to a lung lobe was blocked but ventilation to the lobe was unaffected, how would alveolar gas partial pressures change? PO2 would increase and PCO2 would decrease. If the blood flow to an alveolus were blocked there would be no flow of hemoglobin-rich red blood cells to take away O2 and no influx of CO2 from the blood. As a result the air in the alveolus would become more like that of the atmosphere. It would acquire a higher PO2 and a lower PCO2."

Is this question referring to the pulmonary artery?

Yup

 

[G1SG2]

Yup

"If an artery that supplies blood to a lung lobe was blocked but ventilation to the lobe was unaffected, how would alveolar gas partial pressures change? PO2 would increase and PCO2 would decrease. If the blood flow to an alveolus were blocked there would be no flow of hemoglobin-rich red blood cells to take away O2 and no influx of CO2 from the blood. As a result the air in the alveolus would become more like that of the atmosphere. It would acquire a higher PO2 and a lower PCO2."

See, I didn't know that...I thought it was just a regular artery that was carrying O2 TO the lungs and taking away CO2 from that part of the organ like all arteries do...and so I thought if it were blocked, then the PO2 would decrease (because the artery was blocked) and PCO2 would increase (since the artery wouldn't be able to take away the CO2). How am I to know that's the pulmonary artery they are talking about, especially since all the question said was "if an artery that supplies blood to a lung lobe"?

 

[matth87]

See, I didn't know that...I thought it was just a regular artery that was carrying O2 TO the lungs and taking away CO2 from that part of the organ like all arteries do...and so I thought if it were blocked, then the PO2 would decrease (because the artery was blocked) and PCO2 would increase (since the artery wouldn't be able to take away the CO2). How am I to know that's the pulmonary artery they are talking about, especially since all the question said was "if an artery that supplies blood to a lung lobe"?

An artery going to the lungs will be carrying oxygen poor, co2 rich blood. If it is blocked you will not be able to release co2 into the lungs or pick up new o2. Since under normal circumstance the partial pressure in the lungs of O2 is around 100mmHG and the pp of CO2 is 40mmHG. "Ventilation", air moving in and out of the lungs, is still occurring, but "respiration" or gas exchange with the blood is not. The lungs will shift towards what the atmosphere is like.

The atmosphere has high O2 and very low CO2 compared to the lungs.

The only reason we have CO2 in our lungs is because we make it in our tissue and transfer it to the lungs for release. If this transfer is blocked the amount of CO2 in the lungs will most def decrease.

O2 will be low in the blood, CO2 will be high in the blood, but the question is referring to what will the lungs be like, not the blood. They will be the opposite.

 

[G1SG2]

An artery going to the lungs will be carrying oxygen poor, co2 rich blood. If it is blocked you will not be able to release co2 into the lungs or pick up new o2. Since under normal circumstance the partial pressure in the lungs of O2 is around 100mmHG and the pp of CO2 is 40mmHG. "Ventilation", air moving in and out of the lungs, is still occurring, but "respiration" or gas exchange with the blood is not. The lungs will shift towards what the atmosphere is like.

The atmosphere has high O2 and very low CO2 compared to the lungs.

The only reason we have CO2 in our lungs is because we make it in our tissue and transfer it to the lungs for release. If this transfer is blocked the amount of CO2 in the lungs will most def decrease.

O2 will be low in the blood, CO2 will be high in the blood, but the question is referring to what will the lungs be like, not the blood. They will be the opposite.

That's where the confusion is, I suppose-so ALL arteries going to the lung carry oxygen poor and carbon dioxide rich blood?

 

[kypreos]

I must say that the verbal on this exam is very humbling. I will never think of picasso in the same way again. I now hate him and all of his work. anyways I had a few questions on the PS portion of the test I am hoping some of you can help me out with. I have read through the thread and you guys are very helpfull.

for #9 I am wondering if there is an error with the numbers on the phase diagrahm. cause I kept looking for .1 and saw .3

number 11. an object that is totally immersed in Benzene (specific gravity=.7) is subject to a bouyancy force of 5N. The same object is totally immersed in an unknown liquid BF 12 N. what is the specific gravity of the unknown liquid.

and #31. the pKa for the dissociation oif H2PO4- to HPO4- is 6.7. what is the initial ratio of them in the buffer solution.

I am having trouble solving some multi step problems like #11 and #31.