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!

---

Members don't see this ad.

 

[PocketRocket]

CaSO3 is a solid.....and will not dissolve to any extent. Even if it did dissolve...no SO2 would be produced. If a solid is not in the Keq expression...the addition or removal will have no
EFFECT !!!!!! This is an important concept to know.

Dr. Romano

Thank you!

 

[skyguy1]

#26 qr: Cos(116) =
answer is: -cos(64)
just wondering why sin(64) is wrong since its in the "sin quadrant"

thank you!

 

[DAT Destroyer]

#26 qr: Cos(116) =
answer is: -cos(64)
just wondering why sin(64) is wrong since its in the "sin quadrant"

thank you!

116 is in the second quadrant and cosine is negative in the second quadrant.

 

[super112]

These two questions got lost in the swarm of posts, so I'll repost them here

• 2013 OC question 193. If CH3O- and polar protic, wouldn't this mean E2 reaction? Is it just in this particular problem we bend the rules? B/c when I saw this I initially looked in the answers for "no reaction".


• GC question 208. If I calculate PH = 9, am I supposed to do something fancy to see if indicator with pka 4.4 is in protonated or deprotonated state? I got the right answer by knowing ph =9 is basic, so I simply looked at the deprotonated colors.

Side question: Could I technically use any of the indicator dyes, but it is best if I use one that has pka 1/2 of ph?

Thanks!

 

[FeralisExtremum]

Destroyer 2015 Organic Chemistry #60:

What about all the other non-ring constitutional isomers that could be formed, like heptene, or even the other ring forms like 1,2,3-trimethylcyclobutane? Don't these also count as constitutional isomers?

Destroyer 2015 Organic Chemistry #63:

After the enamine acts as a nucleophile, what makes amine ring leave and get replaced with a ketone again? Don't we need to add acid/water to make that happen?

 

[DAT Destroyer]

Destroyer 2015 Organic Chemistry #60:

What about all the other non-ring constitutional isomers that could be formed, like heptene, or even the other ring forms like 1,2,3-trimethylcyclobutane? Don't these also count as constitutional isomers?

Destroyer 2015 Organic Chemistry #63:

After the enamine acts as a nucleophile, what makes amine ring leave and get replaced with a ketone again? Don't we need to add acid/water to make that happen?

Question 60

The question states for the BELOW molecule.....meaning.....containing the ring ! In the next DESTROYER edition ..I will be a bit more clear. This is a great problem........sorry for any confusion.

Question 63

Either way is fine.....acid sometimes makes it go faster. Water is fine.....the reaction involves attack by the water on the immonium ion intermediate,, this is where the carbonyl O is formed from......,,,,then setting up the amine group as a protonated N as the leaving group. Most organic texts will show this nicely.

Hope this helps.

Dr. Romano

 

[ultimateballer07]

Why would a product of E2 sometimes be Anti-Zaitsev instead of Zaitsev?

 

[Anthony Bogdan]

Why would a product of E2 sometimes be Anti-Zaitsev instead of Zaitsev?

It depends where the anti planar hydrogen is located. Sometimes if it's not available in the more stable location, the least substituted double bond forms

 

[FeralisExtremum]

Why would a product of E2 sometimes be Anti-Zaitsev instead of Zaitsev?

Some common ways this can happen:
(1) Conjugation proximity; form alkene that ends up being conjugated rather than Zaitsev
(2) Tertiary halide with bulky base; can apply to secondary halide + bulky base as well
(3) In a ring: E2 requires backside attack to be anti-axial; might not be possible in a ring, check axial/equatorial status of the substituents.

 

[DAT Destroyer]

Why would a product of E2 sometimes be Anti-Zaitsev instead of Zaitsev?

The distribution of Zaitsev and anti-Zaitsev ... ( Hoffman) products is often dependent on many factors such as conformation, orbitals, stability and not always easy to predict. However, as a general rule for the DAT .....a sterically hindered base such as t-butoxide will give anti-Zaitsev as the major product. The argument is steric. A large base can more easily remove the proton from the outside. For example.....consider 2-bromo-2 methylbutane. Treatment with sodium ethoxide gave 71% Zaitsev product,,,,,,,,a stable alkene resulted. Treatment with t-butoxide gave 92% ANTI - Zaitsev !!!!!!!!! The alkene that resulted was less stable indeed, but was the easiest to form evidently from an easier pathway. For the DAT,,,,,remember.....A large base like t-butoxide ,,,do Anti-Zaitsev ...it is easier to grab the outer hydrogen and not have to dig deep inside .!

Hope this helps.

Dr. Romano

 

[ultimateballer07]

@orgoman22 it definitely helped! Thank you! I've done Destroyer to the point where I can finish the entire workbook section in two hours while getting 95+% correct so I've done each section probably 6-7 times. Hope I can translate on the real thing!

 

[StudentDoc1234]

For Bio Section #92 2015.... I thought aldosterone and vasopressin both have the same effect where they both increase the uptake up water. Is it just that vasopressin has more of an effect than aldosterone?

 

[DAT Destroyer]

@orgoman22 it definitely helped! Thank you! I've done Destroyer to the point where I can finish the entire workbook section in two hours while getting 95+% correct so I've done each section probably 6-7 times. Hope I can translate on the real thing!

Great job UltimateB!

Make sure to carefully go through the Biology, know the correct choices as well as the incorrect choices, there is a lot of information packed into that section. I wish I had a crystal ball and could tell you what to know and that you don't have to know all about plants, etc, but anything is fair game on the DAT, so no choice but to really prepare, Overkill? I say NO, it is the only way be be prepared for whatever comes you way and Destroy the DAT.

Good luck to you and keep up the great work!

Nancy

 

[FeralisExtremum]

For Bio Section #92 2015.... I thought aldosterone and vasopressin both have the same effect where they both increase the uptake up water. Is it just that vasopressin has more of an effect than aldosterone?

Both aldosterone and vasopressin have that effect on the body, but the answer is vasopressin because drinking alcohol specifically blocks its production.

 

[DAT Destroyer]

For Bio Section #92 2015.... I thought aldosterone and vasopressin both have the same effect where they both increase the uptake up water. Is it just that vasopressin has more of an effect than aldosterone?

It has to do with a mechanism of action. Aldosterone causes the reabsorption of Na, which indirectly causes reabsorption of water.

Vasopressin, just causes collecting duct to absorb more water and that is what causes water retention.

Hope this helps.

 

[FeralisExtremum]

DAT Destroyer General Chemistry #194

I understand that for HN3, H+ and N3- dissociate to the same extent. But at equilibrium shouldn't [H+] > [N3-] technically since there is already some (very small) amount of [H+] already in an aqueous solution?

General Chemistry #195

Transition metals are associated with color, but Ag and Cu are both transition metals. How should we determine which one would give a blue color? Does Ag generally only form silver solids?

 

[DAT Destroyer]

DAT Destroyer General Chemistry #194

I understand that for HN3, H+ and N3- dissociate to the same extent. But at equilibrium shouldn't [H+] > [N3-] technically since there is already some (very small) amount of [H+] already in an aqueous solution?

General Chemistry #195

Transition metals are associated with color, but Ag and Cu are both transition metals. How should we determine which one would give a blue color? Does Ag generally only form silver solids?

#194

The amount of hydronium from water is unbelievably small.....for all General Chemistry calculations.....assume a 1 : 1 mole ratio for problems of this type.

#195

Silver Chloride is a commonly asked problem on General Chemistry exams...... It is an opaque white precipitate . ..as is BaSO4. Solutions of most transition metals however give colors.
Some solutions of Silver are colored, indeed. Silver Chromate is Reddish-Brown.

 

[tooth_hurty]

DAT Destroyer 2015 Biology #331

Why does an egg cell contains 23 chromosomes and 23 chromatids? I thought it would have 23 chromosomes and 46 chromatids

 

[FeralisExtremum]

DAT Destroyer 2015 Biology #331

Why does an egg cell contains 23 chromosomes and 23 chromatids? I thought it would have 23 chromosomes and 46 chromatids

In meiosis II, the chromatid pairs split apart and end up in separate gametes. You have 23 chromosomes with 46 chromatids at the end of meiosis I.

 

[tooth_hurty]

In meiosis II, the chromatid pairs split apart and end up in separate gametes. You have 23 chromosomes with 46 chromatids at the end of meiosis I.

Okay thank you. So just want to make sure I have this right: primary oocytes have 46 chromosomes and 46 chromatids after mitosis. Secondary oocytes have 23 chromosomes and 46 chromatids after meiosis I. And egg and sperm cells have 23 chromosomes and 23 chromatids after meiosis II?

 

[FeralisExtremum]

Okay thank you. So just want to make sure I have this right: primary oocytes have 46 chromosomes and 46 chromatids after mitosis. Secondary oocytes have 23 chromosomes and 46 chromatids after meiosis I. And egg and sperm cells have 23 chromosomes and 23 chromatids after meiosis II?

Yep, looks like you've got it all down.

At the end of mitosis of spermatagonium and oogonium you'd have a primary oocyte/spermatcyte with 46 chromosomes and 46 chromatids. Secondary oocytes/spermatocytes have gone through meiosis I, and therefore have 23 chromosomes and 46 chromatids. At the appropriate point in development, these will complete meiosis II and you will have your final gametes (sperm and egg) with 23 chromosomes/chromatids.

Be careful for minor details here, like the fact that meiosis of oocytes produces polar bodies, and that meiosis II of secondary oocytes technically doesn't happen until/unless a sperm penetrates it.

 

[tooth_hurty]

DAT Destroyer 2015 Biology #373

This question states that lysosomes are found in both plant and animal cells, yet Cliffs 3rd ed states on pg 38 that lysosomes are only found in animal cells? Am I missing something?

 

[w4nt2baDDS]

This question states that lysosomes are found in both plant and animal cells, yet Cliffs 3rd ed states on pg 38 that lysosomes are only found in animal cells? Am I missing something?

Lysosomes were thought to be only in animal cells but recent findings suggest/show that plants have lysosomes too.

Cliffs 3rd edition just doesn't have the most recent findings on this. Besides maybe that single fact, I believe Cliffs 3rd edition is still tremendously reliable.

Look up and download "Feralis Biology Notes" it's a great resource and allows for reliable fact checking on discrepancies like this.

 

[DAT Destroyer]

Lysosomes were thought to be only in animal cells but recent findings suggest/show that plants have lysosomes too.

Cliffs 3rd edition just doesn't have the most recent findings on this. Besides maybe that single fact, I believe Cliffs 3rd edition is still tremendously reliable.

Look up and download "Feralis Biology Notes" it's a great resource and allows for reliable fact checking on discrepancies like this.

Thank you w4nt2baDDS, you are quite correct! That is why when developing the Destroyer we are always careful to use the most accurate and up to date info.

take care..Nancy

 

[FeralisExtremum]

DAT Destroyer General Chemistry #333

Solvents which are gases can dissolve other gases - this was not included as a valid expression for "like dissolves like", but is it still a true statement? Or are gases dissolved in gases considered mixtures and not solutions?

DAT Destroyer Biology #475

Aren't answer choices B and D both valid answers?

 

[tooth_hurty]

DAT Destroyer General Chemistry #333

Solvents which are gases can dissolve other gases - this was not included as a valid expression for "like dissolves like", but is it still a true statement? Or are gases dissolved in gases considered mixtures and not solutions?

DAT Destroyer Biology #475

Aren't answer choices B and D both valid answers?

For Bio #475, I think the question is just being very particular about how answer answer B is worded as "the start site for transciption." Although the promoter initiates transcription of the lacZ, lacY and lacA genes, it's not the site where transcription actually starts because the promoter region is not actively transcribed into mRNA. So I still think D is the only correct answer. The wording here is definitely tricky though

 

[w4nt2baDDS]

2014 Math Destroyer -- Test 12 Q.28



How is the answer choice E? I keep getting zero.. even after manipulating things.

 

[FeralisExtremum]

2014 Math Destroyer -- Test 12 Q.28

View attachment 191823

How is the answer choice E? I keep getting zero.. even after manipulating things.

I wrote out how I solved it here: http://i.imgur.com/0BI09e0.jpg

Worst case scenario, you can put in a small test number (make sure to avoid 0 and 1, as these can be special cases) for the variable and then plug and chug.

 

[DAT Destroyer]

DAT Destroyer General Chemistry #333

Solvents which are gases can dissolve other gases - this was not included as a valid expression for "like dissolves like", but is it still a true statement? Or are gases dissolved in gases considered mixtures and not solutions?

DAT Destroyer Biology #475

Aren't answer choices B and D both valid answers?

DAT Destroyer General Chemistry #333

A solution is a mixture of two or more substances in a single phase. At least two substances must be mixed in order to have a solution. The substance in the smallest amount and the one that dissolves or disperses is called the SOLUTE. The substance in the larger amount is called the SOLVENT. In most common instances water is the solvent. The gases, liquids, or solids dissolved in water are the solutes.

Air is classified as BOTH a mixture and a solution.

Hope this helps.

Dr. Romano

 

[DAT Destroyer]

DAT Destroyer General Chemistry #333

Solvents which are gases can dissolve other gases - this was not included as a valid expression for "like dissolves like", but is it still a true statement? Or are gases dissolved in gases considered mixtures and not solutions?

DAT Destroyer Biology #475

Aren't answer choices B and D both valid answers?

Destroyer is correct. Transcription start site is a place where first RNA nucleotide is added to make new RNA strand. Promoter site is where RNA polymerase binds to before transcription starts. Promoter site is usually 10-35 bases before transcription start site.

 

[DAT Destroyer]

2014 Math Destroyer -- Test 12 Q.28

View attachment 191823

How is the answer choice E? I keep getting zero.. even after manipulating things.

Hope this helps!

 

[w4nt2baDDS]

That helps a ton!! Thanks

I was dead in the water fr0m the get go... I miss interpreted the problem as:

 

[super112]

Where does tRNA bind to corresponding amino acid? Cytoplasm or nucleus?

 

[FeralisExtremum]

Where does tRNA bind to corresponding amino acid? Cytoplasm or nucleus?

Cytoplasm.

 

[super112]

Cytoplasm.

Hmm that's what I thought too, but from q211 for bio 2013, this answer choice is supposed to be correct, "When an amino acid enters the cytoplasm from a t-RNA molecule, it first goes to the ribosome." So I must be misinterpreting this; "from" really throws me off.

 

[PocketRocket]

Math destroyer 2015.

Test 16 #5; I can't seem to figure out how B is the right answer. I am convinced that it is C. What am I missing here?

Thanks

 

[FeralisExtremum]

Hmm that's what I thought too, but from q211 for bio 2013, this answer choice is supposed to be correct, "When an amino acid enters the cytoplasm from a t-RNA molecule, it first goes to the ribosome." So I must be misinterpreting this; "from" really throws me off.

Yea the wording on that one threw me off a bit as well. I assume it's supposed to mean something like "When an amino acid binds to a t-RNA molecule in the cytoplasm, it first goes to the ribosome."

 

[alexis2010]

Math destroyer 2015.

Test 16 #5; I can't seem to figure out how B is the right answer. I am convinced that it is C. What am I missing here?

Thanks

The answer is C. Must have been a typo. Just looked at my friends destroyer who just got it and it shows C as the answer.
Like the solution says use the properties of Log. Log(AB) = Log A + Log B
Log(A/B) = Log A -Log B
Log(A^n)=nLog A.
Best of luck

 

[alexis2010]

I didn't even know this thread existed, now I'm gonna bother you guys with my questions

 

[StudentDoc1234]

I know there are different ways to get the same answer for many problems, I just want to make sure if I can keep using this method for this type of problem.

It's for 2015 #228 Gchem
I used the ICE BOX method and wrote the equation for CO2: 3x = 3x10^-4 which lead me to x=10^-4. From there I used that value of x and applied it to 5x for O2 giving me the answer of 5x10^-4.

 

[SCDP]

So I should definitely go through destroyer twice right?

 

[DAT Destroyer]

I know there are different ways to get the same answer for many problems, I just want to make sure if I can keep using this method for this type of problem.

It's for 2015 #228 Gchem
I used the ICE BOX method and wrote the equation for CO2: 3x = 3x10^-4 which lead me to x=10^-4. From there I used that value of x and applied it to 5x for O2 giving me the answer of 5x10^-4.

The easier way is to simply examine the mole ratios.......O2 is larger than CO2,,,,,,yes ? How much larger ? 5/3 larger......by simply examining the coefficients..... therefore simply multiply 3x10 exp-4 by this factor....5/3. The ADA practice exams have another one for you to practice.

Hope this helps

Dr. Romano

 

[PocketRocket]

Gen Chem 2015 Q 118:

In the explanation it says that C4H10 has greater deltaS than C3H8 due to it having more atoms and greater molecular complexity. How come we don't take into account the greater intermolecular forces in butane compares to propane. I would think that because of the forces butane is more "compact" than propane and therefore would have a smaller deltaS. Also, its not like the atoms dissociate from each other in the molecule so how come you take their number into account?

 

[FeralisExtremum]

Gen Chem 2015 Q 118:

In the explanation it says that C4H10 has greater deltaS than C3H8 due to it having more atoms and greater molecular complexity. How come we don't take into account the greater intermolecular forces in butane compares to propane. I would think that because of the forces butane is more "compact" than propane and therefore would have a smaller deltaS. Also, its not like the atoms dissociate from each other in the molecule so how come you take their number into account?

I had the same ΔS/molecular complexity question as you when I was studying...when I looked into it the only solid explanation I could find was that with greater molecular complexity we have more moving electrons (and therefore more "disorder" overall). Another source said it was due to "more possible vibrational and rotational modes". At that point I figured knowing such information was low yield and just made a note of the fact that molecular complexity increases ΔS.

 

[DAT Destroyer]

Gen Chem 2015 Q 118:

In the explanation it says that C4H10 has greater deltaS than C3H8 due to it having more atoms and greater molecular complexity. How come we don't take into account the greater intermolecular forces in butane compares to propane. I would think that because of the forces butane is more "compact" than propane and therefore would have a smaller deltaS. Also, its not like the atoms dissociate from each other in the molecule so how come you take their number into account?

When talking about " compact " we usually refer to molecules that are either branched or cyclic. Propane and butane are straight chained. The reason why the number of atoms are taken into account is a reason of molecular complexity.....with more atoms....there are more electrons, orbitals, and molecular vibrations, rotations, etc. Butane would have the greater entropy than propane. From the literature values for entropy.....Propane is about 230J/moleK...and butane is 270 J/moleK

Hope this helps

Dr. Jim Romano

Hope this helps.

 

[DentalGirl5]

Hi Orgoman (and woman)
GC 2014 #99,
What does CaCl2 * 2H2O even mean? I'm having such a hard time grasping why the answer would be 111 + 36. I get that that's adding the MW of CaCl2 and 2 H2O's, but I don't think I'm understanding the deeper meaning of this question. How could this make a 1M solution? Isn't M = moles solute/Liters solution? Wouldn't that just be moles of CaCl2/Liters of H2O? Or is the CaCl2 * H2O all one "compound" so it's implying that the combined MW of these would be equivalent to one mole of the "solute" and then it would be dissolved in one Liter of solution? Thank you

 

[DAT Destroyer]

Hi Orgoman (and woman)
GC 2014 #99,
What does CaCl2 * 2H2O even mean? I'm having such a hard time grasping why the answer would be 111 + 36. I get that that's adding the MW of CaCl2 and 2 H's, but I don't think I'm understanding the deeper meaning of this question. How could this make a 1M solution? Isn't M = moles solute/Liters solution? Wouldn't that just be moles of CaCl2/Liters of H2O? Or is the CaCl2 * H2O all one "compound" so it's implying that the combined MW of these would be equivalent to one mole of the "solute" and then it would be dissolved in one Liter of solution? Thank you

CaCl2 is a hydrate.....a solid crystal that contains water. A 1M solution simply means 1 mole of this compound in a liter. Recall...a MOLE is not only an amount of particles....BUT, the atomic or molecular weight expressed in grams. Essentially.....you are finding the mass of this compound.

Hope this helps.

Dr. Jim Romano

 

[tyjacobs]

DAT organic chemistry odyssey chapter 13 question 6,

so in the reaction scheme, i understand that the first reagent will cause a markovnikov addition of OH and H without any carbocation shifts.

the second reagent will convert the secondary alcohol into the ketone.

but what i don't understand is the addition of NH3 to a ketone. I have been told from watching organic chemistry lectures at UC irvine that NH3 when added to an aldehyde or ketone will generate a very unstable "imine" and you typically wouldn't see this reaction. So in theory, wouldn't the correct answer be a ketone?

DAT organic chemistry odyssey chapter 13 question 38,

why is the answer A not D?

DAT organic chemistry odyssey chapter 12 question 10,

why is the group a deactivating group? You clearly see that the sulfur attached to the benzene has a lone pair, so wouldn't this mean that its an electron donor group?

DAT organic chemistry odyssey chapter 12 question 13,

Is the difference between electron pair A and electron pair D purely based on % s character?

DAT organic chemistry odyssey chapter 12 question 36,

why are acetals ortho/para directors if the atom directly bound to the benzene has no lone pairs and has the two oxygen groups directly attached? Is it because the dipoles cancel out and therefore you can treat it like an "alkyl group"?

Also just a general question from the substitution reactions chapters:

If you have a secondary alkyl halide and you react it with a non-bulky but strong base, I know you get a mixture of E2 and SN2. Is E2 favored over Sn2 though?

For example (i am referencing organic chem odyssey problems): chapter 8 question 33 (the Iodine bound to the cyclohexane undergoes E2) and chapter 8 question 9 (the iodine bound to cyclopentane undergoes Sn2 even though there is beta branching from the adjacent methyl group). Just curious on the rationale for the two questions why one is favored over the other

 

[cacajuate]

Destroyer '15 OC #285.


Why can't A be reduced?

Don't we just end up with the same molecule after oxidation and reduction?

 

[DAT Destroyer]

Destroyer '15 OC #285.


Why can't A be reduced?

Don't we just end up with the same molecule after oxidation and reduction?

Alcohols do not get reduced.....only oxidized. Molecules such as aldehydes, ketones, nitriles, acyl halides, alkenes, alkynes, imines, esters, and acids get reduced.

Hope this helps.

Dr. Romano