Official DAT Destroyer Q&A Thread

[densaugeo]

Hi guys, since I'm currently going through the DAT Destroyer and I'm sure many of you guys are as well I felt this thread would be helpful. I usually have various questions while going through Destroyer regarding why a certain answer choice is correct or other times I am in need of a more detailed explanation.

Instead of making multiple threads each time we have questions, I thought we could just post them here and anyone can chime in with an explanation or further clarification.

Please don't post entire questions as that would be a violation of copyright. You can ask specific questions regarding a particular problem in the Destroyers.

Hopefully others find this a useful thread. Thanks!

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[mrdeez]

BIO #543 in 2016 destroyer asks for the longest stage of the cell cycle. The solution says it is G1 of interphase. I thought it was S phase?

Campbell's Biology (9th edition) seems to agree. I've bolded and underlined portions of the text that indicate this below. Let me know what you think.

"A particular human cell might undergo one division in 24 hours. Of this time, the M phase would occupy less than 1 hour, while the S phase might occupy about 10-12 hours or about half the cycle. The rest of the time would be apportioned between the G1 and G2 phases. The G2 phase usually takes 4-6 hours; in our example, G1 would occupy about 5-6 hours. G1 is the most variable in length in different types of cells."

-Campbell Biology, 9th edition

 

[Florida Dent]

DAT Destroyer 2017
General Chemistry problem #354

When comparing the mole ratios, why does the 2 moles of KClO3 cancel out? Why don't you divide by 2 then multiply by 3? Thanks

 

[DAT Destroyer]

DAT Destroyer 2017
General Chemistry problem #354

When comparing the mole ratios, why does the 2 moles of KClO3 cancel out? Why don't you divide by 2 then multiply by 3? Thanks

No. You are given grams of KClO3 and are asked about Oxygen. The mole ratio of KCl is not important. Review my solution on this problem. If you still have a problem, any intro Gen Chem book will do more examples. The chapter you will review will be on mole stoichiometry.

Hope this helps.

Dr. Romano

 

[DAT Destroyer]

Older destroyer, but the question is: A somatic cell during interphase has X chromosomes. How many chromatids?

Do you assume that the cell has replicated its DNA and thus has 2X chromatids? I put X and got it wrong so :/

Thank you to anyone who helps!

Yes. Somatic cell has 2X.

 

[drobgyn32]

GC #120. Why does H2NO3 end up losing water? How were we supposed to know that this was the following step?

Thank you

 

[DAT Destroyer]

GC #120. Why does H2NO3 end up losing water? How were we supposed to know that this was the following step?

Thank you

drobgyn32, Great question. Think of it an easy way.....H2SO4 has ENORMOUS resonance stabilization in the HS04- anion, and would be much stronger than HN03 as an acid. Now that we know it ( H2S04 ) is the acid, it will donate an H+ to the HN03.... Now, once protonated, you should recognize that water is a good leaving group. As water leaves, it leaves us with the NO2+ ion. Recall this is the exact ion that was used in Organic chemistry when benzene was nitrated. Bottom line.....H2S04 is a stronger acid than HN03.

Hope this helps.

Dr. Romano

 

[spdental]

Dr. Romano,

Question 62 of the O-Chem 2007 Destroyer I believe has a mistake. I don't believe product 1 is chiral, so we should only have 5 products. Is this correct?

 

[DAT Destroyer]

Dr. Romano,

Question 62 of the O-Chem 2007 Destroyer I believe has a mistake. I don't believe product 1 is chiral, so we should only have 5 products. Is this correct?

The problem is correct. Most students get this wrong. Look closely at product 1.....This compound is indeed chiral at carbon number 2 !!! When a Cl is placed on a chiral, that usually makes that particular carbon chiral, but NOT always. Thus, 6 products are produced. The best way to do this is the way I teach my students. Check to see that EVERY carbon is chiral or not !!! I think you meant the 2017 version of the book, as this problem was not in our earlier edition. I hope this clears this up.

 

[drobgyn32]

2017 #262 makes no sense to me at all. I get the formula, but which formula do I use for what?
P1V1/T1= P2V2/T2
What do I plug in on the left? JUST dry gas?
If so, what do I plug in on the right?
Where do I use 740? Where do I use 760?

Totally confused...If anyone can help, I will be very grateful. Thank you.

 

[spdental]

On question 103 of the 2017 O Chem section, I was wondering why adding a NaI to a 3 - chloropentane would yield a product? Isn't I a better leaving group than Cl? Therefore wouldn't it make it difficult to react?

 

[DAT Destroyer]

2017 #262 makes no sense to me at all. I get the formula, but which formula do I use for what?
P1V1/T1= P2V2/T2
What do I plug in on the left? JUST dry gas?
If so, what do I plug in on the right?
Where do I use 740? Where do I use 760?

Totally confused...If anyone can help, I will be very grateful. Thank you.

The terms P1, V1, and T1 refer to the INITIAL CONDITIONS..,,,,,the terms P2, V2, and T2 refer to the final conditions. The final conditions are the STP conditions that you are REQUIRED to know. They are 273K which is the T2 term, and 1 atm which is the P2 term. I hope this helps. This is a standard , but very important problem.
If you are still lost, consult a General Chem text book and read about collecting a gas over water.

Hope this helps..

Dr. Jim Romano

 

[drobgyn32]

The terms P1, V1, and T1 refer to the INITIAL CONDITIONS..,,,,,the terms P2, V2, and T2 refer to the final conditions. The final conditions are the STP conditions that you are REQUIRED to know. They are 273K which is the T2 term, and 1 atm which is the P2 term. I hope this helps. This is a standard , but very important problem.
If you are still lost, consult a General Chem text book and read about collecting a gas over water.

Hope this helps..

Dr. Jim Romano

Thank you! Also, for 316...why is the answer activated complex and not transition state? What is the difference between the two? Thank you

 

[DAT Destroyer]

On question 103 of the 2017 O Chem section, I was wondering why adding a NaI to a 3 - chloropentane would yield a product? Isn't I a better leaving group than Cl? Therefore wouldn't it make it difficult to react?

Iodine is not only a good leaving group, but it is an excellent nucleophile . This reaction that you reference is the famous Finkelstein reaction and used extensively in organic chemistry, It is the prototype of all SN2 reaction mechanisms.

Hope this helps.

Dr. Romano

 

[DAT Destroyer]

Thank you! Also, for 316...why is the answer activated complex and not transition state? What is the difference between the two? Thank you

The transition state represents the point of highest energy. The arrangements of atoms within the transition state represents the activated complex. Hope this helps.

 

[drobgyn32]

The transition state represents the point of highest energy. The arrangements of atoms within the transition state represents the activated complex. Hope this helps.

I understand, thank you! Lastly, #344. I don't get how A and B increase the volume of the base. This question really confuses me. It takes a lot of time to think this in depth during the exam.

 

[DAT Destroyer]

I understand, thank you! Lastly, #344. I don't get how A and B increase the volume of the base. This question really confuses me. It takes a lot of time to think this in depth during the exam.

Using water would mean that more base would have to be used to make up for the diluted volume. Water will cause base DILUTION !!!! Using NaOH that absorbed CO2 means that more would be needed to make up for it...Both of these would necessitate using more NaOH.

Hope this helps.

Dr. Romano

 

[TigerDK]

Edit:
DAT Destroyer 2017 #271 Ochem

I have no idea how to approach this problem. When theres two rings attached, do you count them separately? If the rings are counted together, then it's 10 carbons and wouldn't be planar. If counted separately, the right one only has 4 electrons. I'm pretty lost.

 

[DAT Destroyer]

Edit:
DAT Destroyer 2017 #271 Ochem

I have no idea how to approach this problem. When theres two rings attached, do you count them separately? If the rings are counted together, then it's 10 carbons and wouldn't be planar. If counted separately, the right one only has 4 electrons. I'm pretty lost.

You need to review aromaticity before doing these problems. Each double bond simply counts as 2 electrons. Here we have 5 double bonds associated with the ring system, thus 10 pi electrons are noted. This is an aromatic molecule. I would suggest the David Klein text. An older edition is fine. The chapter on aromaticity is written in a very easy to understand style.

I hope this helps.

Dr. Romano

 

[TigerDK]

You need to review aromaticity before doing these problems. Each double bond simply counts as 2 electrons. Here we have 5 double bonds associated with the ring system, thus 10 pi electrons are noted. This is an aromatic molecule. I would suggest the David Klein text. An older edition is fine. The chapter on aromaticity is written in a very easy to understand style.

I hope this helps.

Dr. Romano

I understand those characteristics of aromaticity, but according to Chad's videos, if the compound has more than 7 carbons, it is generally not planar and therefore would not aromatic. If all the carbons are counted, then there are 10 carbons. Would this be an exception to that case?

 

[DAT Destroyer]

I understand those characteristics of aromaticity, but according to Chad's videos, if the compound has more than 7 carbons, it is generally not planar and therefore would not aromatic. If all the carbons are counted, then there are 10 carbons. Would this be an exception to that case?

That is an untrue statement . Hundreds of aromatic compounds are larger than 7 carbons. Anthracene, phenanthrene, tetracene, azulene, come to mind.The ring can indeed be more than 7 carbons. Many annulenes are also aromatic . A Google search will show them to you. The 18 carbon ringed molecule called ( 18 ) annulene is a fine example. This is easily confirmed by NMR studies and spectroscopic analysis. In hemoglobin, we have the monstrous porphyrin ring that is indeed aromatic. Consult any standard organic text written by PhD Chemists to see hundreds more. My favorite books are Klein, Wade, Jones, McMurray, Bruice, Carey, Smith, and Clayden.

Hope this helps.

Dr. Romano

 

[Dallas Dentist]

General Chemistry #215:
I don't understand how the solution explains it. How can you assume that the K values given are the Ka's?

 

[drobgyn32]

General Chemistry #215:
I don't understand how the solution explains it. How can you assume that the K values given are the Ka's?

Since it said the K values are for H3PO4 (an acid), it can be assumed that they are Ka.

 

[spdental]

Dr. Romano,

In Gen Chem 2017,the answer for 174 you first mention that we should recall PV=nRT, and that since the moles don't change, the pressure temp, or volume will not.

However, you then mention to recall P(MW) = DRT and that since He is lighter, the molecular weight will be less, and if we decrease the mass of the gas, the density will decrease. If we are using the second equation, why wouldn't decreasing the mass also increase the pressure, and decrease the temperature? I guess I'm wondering why once we bring in the second equation, we are only using it for density rather than temp, pressure, etc.

 

[DAT Destroyer]

Dr. Romano,

In Gen Chem 2017,the answer for 174 you first mention that we should recall PV=nRT, and that since the moles don't change, the pressure temp, or volume will not.

However, you then mention to recall P(MW) = DRT and that since He is lighter, the molecular weight will be less, and if we decrease the mass of the gas, the density will decrease. If we are using the second equation, why wouldn't decreasing the mass also increase the pressure, and decrease the temperature? I guess I'm wondering why once we bring in the second equation, we are only using it for density rather than temp, pressure, etc.

Dr. Romano is currently in a DAT Lecture, he will respond this afternoon.

Nancy

 

[JrjDDS]

On Destroyer Bio #149

The answer states that it is correct that cardiac and smooth muscle are both mononucleated. I have been taught this is not correct, that cardiac muscle can have two nuclei, or be mononucleated, but i feel like that could be a trap to exclude the possibility of 2?

clarification would be great, thanks.

Also on #158 in the 2017version, the answer description is confusing. I think it is the answer description to a different question.

 

[drobgyn32]

MATH DESTROYER Test 3 #10... How are we getting 70 degrees? This is my diagram so far. I'm so stuck.

 

[DAT Destroyer]

Dr. Romano,

In Gen Chem 2017,the answer for 174 you first mention that we should recall PV=nRT, and that since the moles don't change, the pressure temp, or volume will not.

However, you then mention to recall P(MW) = DRT and that since He is lighter, the molecular weight will be less, and if we decrease the mass of the gas, the density will decrease. If we are using the second equation, why wouldn't decreasing the mass also increase the pressure, and decrease the temperature? I guess I'm wondering why once we bring in the second equation, we are only using it for density rather than temp, pressure, etc.

PV = nRT was used to DERIVE the needed mathematical equation which was P(MW) = DRT. Thus by looking at the density equation, we note that a lighter mass of a given gas would indeed change the density. For example, if you filled a balloon up with Ar gas, it would fall to the floor . If you now used Helium gas, we would see the balloon fly away. Using this example, I hope you could see that volume, moles, and temperature would indeed remain the same. This is a very commonly asked trick question.

I hope studies are going well, and this helps.

Dr. Romano

 

[UNCafDDS]

For Destroyer OC 2016, question #270.....
Rank the following molecules in decreasing order (most acidic first) of acidity.
I is a terminal alkyne
II is a carboxylic acid
III is a benzylcarboxylic acid
IV is an alcohol
V is a ketone

It says the answer is B (III > II > I > V), but I think it is A (III >II > IV > V > I).

I was taught that terminal alkynes had acidic protons, so I assumed that I was more acidic than V. The answer key mentions an amine, which is not even in the picture. So I feel like there may be a typo? Or are ketones really more acidic than terminal alkynes.

 

[spdental]

For Destroyer OC 2016, question #270.....
Rank the following molecules in decreasing order (most acidic first) of acidity.
I is a terminal alkyne
II is a carboxylic acid
III is a benzylcarboxylic acid
IV is an alcohol
V is a ketone

It says the answer is B (III > II > I > V), but I think it is A (III >II > IV > V > I).

I was taught that terminal alkynes had acidic protons, so I assumed that I was more acidic than V. The answer key mentions an amine, which is not even in the picture. So I feel like there may be a typo? Or are ketones really more acidic than terminal alkynes.

Dr. Romano may be able to give you a better answer, but I believe that the ketone is more acidic due to resonance with the Oxygen. Take a look at the picture I posted showing the relative pKas.

 

[DAT Destroyer]

The Pka of benzoic acid is about 4....a carboxy acid is about 5......an alcohol is 16......a ketone is about 18...and the alkyne is 25. Clearly the alkyne is the LEAST acidic. For further clarification, the David Klein text book will present these similar values. The alkyne having the highest pKa would be the least acidic. When doing a synthesis, the terminal alkyne is indeed reasonably acidic, but hopefully you recall that you used a VERY STRONG base such as sodamide, NaNH2 to remove it. The problem in DESTROYER stands correct.


Hope this helps

Dr. Romano

 

[DAT Destroyer]

On Destroyer Bio #149

The answer states that it is correct that cardiac and smooth muscle are both mononucleated. I have been taught this is not correct, that cardiac muscle can have two nuclei, or be mononucleated, but i feel like that could be a trap to exclude the possibility of 2?

clarification would be great, thanks.

Also on #158 in the 2017version, the answer description is confusing. I think it is the answer description to a different question.

Destroyer is correct. Cardiac muscle cells are predominantly mononucleated. They have lots of mitochondria, however. They have striations and 3 types of layers, Endocardium, Myocardium, and Epicardium. You may see more than one nuclei in those cells if some cells decide to regenerate. It may happen as a result of trauma and with specific stimulating factors.

Hope this helps.

 

[UNCafDDS]

The Pka of benzoic acid is about 4....a carboxy acid is about 5......an alcohol is 16......a ketone is about 18...and the alkyne is 25. Clearly the alkyne is the LEAST acidic. For further clarification, the David Klein text book will present these similar values. The alkyne having the highest pKa would be the least acidic. When doing a synthesis, the terminal alkyne is indeed reasonably acidic, but hopefully you recall that you used a VERY STRONG base such as sodamide, NaNH2 to remove it. The problem in DESTROYER stands correct.


Hope this helps

Dr. Romano

Makes sense! Thank you!

 

[DAT Destroyer]

Makes sense! Thank you!

Glad I could help.

When are you taking your DAT? Have you completed the Destroyer at least once?

 

[spdental]

For question 238 on Destroyer OChem 2017, I was under the impression that we used the order with the least lowest sum of substituents possible, in this case shouldn't it be C? Why would B be the answer here?

 

[Dallas Dentist]

Question 418 Destroyer 2017 Bio:
I thought lysosomes aren't found in plant cells so how is B also not a correct answer here? The solutions say only A is the answer.

 

[DAT Destroyer]

Question 418 Destroyer 2017 Bio:
I thought lysosomes aren't found in plant cells so how is B also not a correct answer here? The solutions say only A is the answer.

Some plant cells do have lysosomes, just not as much as animal cells.

 

[DAT Destroyer]

For question 238 on Destroyer OChem 2017, I was under the impression that we used the order with the least lowest sum of substituents possible, in this case shouldn't it be C? Why would B be the answer here?

The OH is the main functional group, thus must be assigned #1. From that point, the lowest number would be achieved as shown in the solution., making the carbon with the Br. as #2. The lowest number is a nice rule of thumb,,,but you MUST watch out for the key functional group, here it is the alcohol. Consult any organic text for more examples.
I hope this helps.

Dr. Romano

 

[spdental]

The OH is the main functional group, thus must be assigned #1. From that point, the lowest number would be achieved as shown in the solution., making the carbon with the Br. as #2. The lowest number is a nice rule of thumb,,,but you MUST watch out for the key functional group, here it is the alcohol. Consult any organic text for more examples.
I hope this helps.

Dr. Romano

So it's lower number substituent first not lower number of total substituents? for example 2+5+5 vs 2+2+5.

 

[DAT Destroyer]

So it's lower number substituent first not lower number of total substituents? for example 2+5+5 vs 2+2+5.

That is correct. If you have an alcohol......give that carbon with the OH group the LOWEST number. If you have an alcohol and a ketone for example, the ketone group gets the priority. I have read virtually every textbook in the United States, India, and Great Britain. I think there are two that stand out as very easy to read for the beginning student, and would highly advise one of two texts for you to peruse. My favorite is the David Klein text......then the Francis Carey text. Both are easy to read and contain many examples. An older edition of the book is fine.

It is imperative that you review functional group nomenclature.

I hope this helps

Dr. Romano

 

[spdental]

That is correct. If you have an alcohol......give that carbon with the OH group the LOWEST number. If you have an alcohol and a ketone for example, the ketone group gets the priority. I have read virtually every textbook in the United States, India, and Great Britain. I think there are two that stand out as very easy to read for the beginning student, and would highly advise one of two texts for you to peruse. My favorite is the David Klein text......then the Francis Carey text. Both are easy to read and contain many examples. An older edition of the book is fine.

It is imperative that you review functional group nomenclature.

I hope this helps

Dr. Romano

That's a lot of textbooks

Thanks again.

 

[goprodent2]

DAT Destroyer #10 Ochem.

Im looking at the answer and I thought it would be 4 monobrominated products. What i'm thinking is (if looking at the third answer on right) there would be a Bromine on the last hexane ring. Can you please show hoe if I were to place a bromine on the last ring that it wold still come out to be a duplicate. Thank you

 

[RDHtoDDS_40]

Does anyone have a sample schedule of how many questions per day to do for each subject in the DAT destroyer to finish it in a month? Any advice would be appreciated!

 

[UNCafDDS]

1. If I have the 2016 Math Destroyer + the extra questions that Orgoman recently posted for the new quantitative comparison..... is that as good as the 2017 version? My test is in 3 weeks, and I am not sure if I need 2016 + 2017 Math Destroyer.

2. How does Math Destroyer relate to the actual DAT? Is Destroyer about the same? Harder?

Thanks!

 

[goprodent2]

1. If I have the 2016 Math Destroyer + the extra questions that Orgoman recently posted for the new quantitative comparison..... is that as good as the 2017 version? My test is in 3 weeks, and I am not sure if I need 2016 + 2017 Math Destroyer.

2. How does Math Destroyer relate to the actual DAT? Is Destroyer about the same? Harder?

Thanks!

What questions are posted? There is new questions for the DAT?

 

[goprodent2]

For Question 17, QR of Dat destroyer. Answer says it's B, answered for area is double, but then goes on to say it's quadrupled (which should e the answer). Is this an error or is the area doubled?

 

[goprodent2]

For 2017 Dat destroyer, when looking at the answers, why is is the formula for 27 different than 20. why is there the extra (r!) in the denominator? I don't know when to use/incorporate the extra (r!) in the formula.

Thanks for the help!

 

[Wererew]

For Question 17, QR of Dat destroyer. Answer says it's B, answered for area is double, but then goes on to say it's quadrupled (which should e the answer). Is this an error or is the area doubled?

I have the 2017 version and the answer says choice D (area is quadrupled) is the right answer.

 

[Wererew]

For 2017 Dat destroyer, when looking at the answers, why is is the formula for 27 different than 20. why is there the extra (r!) in the denominator? I don't know when to use/incorporate the extra (r!) in the formula.

Thanks for the help!

You should look up when to use permutation vs combination probability type of questions

 

[revo14]

Question 4 , QR test 18 , 2017 version

why is answer A inversed, I understand the product of constant proportionality here, that is "a" and "b" are inverses of each other, a.b =K (constant) , but answer doens't make sense to me.

Thanks

 

[goprodent2]

I have the 2017 version and the answer says choice D (area is quadrupled) is the right answer.

Yeah i have the 2017 version as well. It just may be a typo. I agree it should be D, but it says B.

You should look up when to use permutation vs combination probability type of questions

Thank you.