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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[DAT Destroyer]

I'm extremely confused on an elementary topic, please help
Triple bonds>double bonds>single bonds in terms of vibration frequency
If they are all single bonds, the lightest pair of atoms has the highest vibration frequency?

--also, if triple bonds vibrate with a higher frequency, why do sigma antibonding orbitals have a higher energy than antibonding pi orbitals?

Two atoms function as masses, and the covalent bond functions as a SPRING....As the bond strength increases, the vibrational frequency INCREASES,,,,,,,,,whereas a weaker bond leads to a LOWER vibrational frequency. Thus as you can see,,,,,mass is not the main factor here.......but bond strength is....... As for your other question.......This question is well beyond the scope of the DAT exam, but the reason that a sigma antibonding orbital is of higher energy than that of a pi antibonding orbital comes from deep Quantum Mechanics studies. More nodes or regions of zero electron density reside at the nodes, hence the greater the energy. Hope this helps. For the DAT exam....understand that the larger the IR number, the STRONGER the bond.....understand that this technique involves vibrational modes......along with bond stretching. Critical IR numbers include 1720 for carbonyls, 1650 for alkenes....2200 for alkynes and nitriles.....3200 broad for alcohols....and 3200 sharp for amines, Conjugation lowers the IR number.

Hope this helps....

Dr. Romano

 

[molarbear8895]

Destroyer 2016 GCHEM #87

The answer says the molecule NbPO4 is Niobium (III) phosphate.
How come the number is included in this name? I thought we do not include numbers with polyatomic ions?

Thanks!

 

[DAT Destroyer]

Destroyer 2016 GCHEM #87

The answer says the molecule NbPO4 is Niobium (III) phosphate.
How come the number is included in this name? I thought we do not include numbers with polyatomic ions?

Thanks!

Since you have a transition metal, you must include its Oxidation number as a Roman numeral.

Hope this helps.

 

[molarbear8895]

Ooh thank you, I didn't know that!

 

[Hard Work Pays Off]

there is a question in orgo destroyer 2015, # 212 that says a grignard wouldn't react with a diethyl ether because it does not have an acidic hydrogen. So there are many rules on what qualifies as acidic hydrogen and I feel like I'm missing some, so
1- if you have a carbonyl group or a nitrile group the acidic hydrogen would be on the alpha carbon
2- the hydrogen bond to the biggest atom is acidic
3- the hydrogen bond to the most electronegative atom is acidic
so based on these "rules" which would be the more acidic hydrogen in acetic acid? and how come propyne has any acidic hydrogens?
I keep confusing myself, thanks!

 

[DAT Destroyer]

there is a question in orgo destroyer 2015, # 212 that says a grignard wouldn't react with a diethyl ether because it does not have an acidic hydrogen. So there are many rules on what qualifies as acidic hydrogen and I feel like I'm missing some, so
1- if you have a carbonyl group or a nitrile group the acidic hydrogen would be on the alpha carbon
2- the hydrogen bond to the biggest atom is acidic
3- the hydrogen bond to the most electronegative atom is acidic
so based on these "rules" which would be the more acidic hydrogen in acetic acid? and how come propyne has any acidic hydrogens?
I keep confusing myself, thanks!

This question gets me dizzy......The Hydrogen on the Carboxy acid O has a pKa of 5,,,,,thus....this is the acidic H....by removing this Hydrogen, we stabilize the anion by resonance. .... In carbonyl compounds,,,,,like aldehydes and ketones.......the pKa is much much higher....like 17 or 18. A nitrile and ester is around 25.....an alkyne too ! Again.....anion stabilization !!! Propyne is acidic because the anion is STABILIZED........which is the general reason for most acid trends. I want you to get the David Klein text.....and read the chapter on acidity.....then I invite you back.....once you master these basics..... you and I will spar on any other questions you have !!!!

Looking forward to hearing from you again !!!

Dr. Romano

 

[dentalpredent2016]

I know GC #172 was on here before, and I understand the idea of normality.
But I still don't understand how from the question you know that they're asking for when NaVa=NbVb

How do you know that it's asking for mol A = mol B..?

 

[DAT Destroyer]

I know GC #172 was on here before, and I understand the idea of normality.
But I still don't understand how from the question you know that they're asking for when NaVa=NbVb

How do you know that it's asking for mol A = mol B..?

In order to Neutralize an Acid, one needs the concentration of H+ ions to equal to the concentration of OH- ions. In this problem, Ca(OH)2 has twice as many OH- ions as HBr. Therefore, you need to use Normality equation in order to calculate the correct concentration of acid (HBr).

Hope this helps.

 

[zyzzbruh]

Hey, i'm confused again

I was calculating the pH of diprotic sulfuric acid given a particular concentration, and remembered that only the first proton is strongly acidic, while the second proton is weakly acidic, so the pH will be slightly lower than my answer.
ex) the pH of 0.001M H2SO4 is slightly less than 3 but slightly more than 2.7
so.. I understand this.. we calculate H2SO4 how we would any other strong acid, and assume our answer is slightly more acidic..

BUT what about a question that contains a given concentration of a triprotic acid like phosphoric acid?
This acid is not strong, so they have to give us a ka value..
Would we calculate the pH how we normally do for weak acids, and assume the correct answer is slightly lower?
Do we have to triple the concentration?
Given one ka value, can we only calculate the pH of the first proton dissociating? Or all 3?
Would we need 3 ka values?

 

[DAT Destroyer]

Hey, i'm confused again

I was calculating the pH of diprotic sulfuric acid given a particular concentration, and remembered that only the first proton is strongly acidic, while the second proton is weakly acidic, so the pH will be slightly lower than my answer.
ex) the pH of 0.001M H2SO4 is slightly less than 3 but slightly more than 2.7
so.. I understand this.. we calculate H2SO4 how we would any other strong acid, and assume our answer is slightly more acidic..

BUT what about a question that contains a given concentration of a triprotic acid like phosphoric acid?
This acid is not strong, so they have to give us a ka value..
Would we calculate the pH how we normally do for weak acids, and assume the correct answer is slightly lower?
Do we have to triple the concentration?
Given one ka value, can we only calculate the pH of the first proton dissociating? Or all 3?
Would we need 3 ka values?

No.....a Triprotic acid is not likely to appear on a multiple choice exam. A quadratic equation would be needed. However,,,,I have partially addressed this with my students. We took a triprotic acid such as Phosphoric acid and we wrote all 3 ionization steps out.....and wrote the Ka equation for each of the steps. This would be more appropriate for a multiple choice exam like the DAT. Hope this helps.

 

[DentalNucleicAcid]

Hey Doc or anyone, I'm in need of some minor clarification on the acrosomal reaction in fertilization. I'm not sure exactly what triggers the release of the acrosomal enzymes, is it the contact between the sperm head and the jelly coat of the egg or is it the binding of the acrosomal process proteins to the ZP3 receptors on the zona pellucida? It seems like it's the latter, but if so, then what are the enzymes that are released that digest the jelly coat upon contact with the egg? Thank you

 

[DAT Destroyer]

Hey Doc or anyone, I'm in need of some minor clarification on the acrosomal reaction in fertilization. I'm not sure exactly what triggers the release of the acrosomal enzymes, is it the contact between the sperm head and the jelly coat of the egg or is it the binding of the acrosomal process proteins to the ZP3 receptors on the zona pellucida? It seems like it's the latter, but if so, then what are the enzymes that are released that digest the jelly coat upon contact with the egg? Thank you

You are correct. There is a receptor binding interaction between the receptors of the Zona Pellucida and ligands from the sperm. The nature of all of those molecules is not completely elucidated yet.
The Acrosome reaction takes place by the following steps.
First the sperm is releasing Hyaluronidase to penetrate the Corona radiata. Then, it releases the enzyme called Acrosin, to penetrate Zona Pellucida.

Hope this helps.

 

[DentalNucleicAcid]

You are correct. There is a receptor binding interaction between the receptors of the Zona Pellucida and ligands from the sperm. The nature of all of those molecules is not completely elucidated yet.
The Acrosome reaction takes place by the following steps.
First the sperm is releasing Hyaluronidase to penetrate the Corona radiata. Then, it releases the enzyme called Acrosin, to penetrate Zona Pellucida.

Hope this helps.

Awesome, exactly what I was looking for. Thanks!

 

[DAT Destroyer]

Awesome, exactly what I was looking for. Thanks!

 

[bballjake300]

In the destroyer on the bio section #251 it says that stratum germinativum is the deepest layer of the epidermis..however, in feralis notes the deepest layer is basale?

 

[DentalNucleicAcid]

In the destroyer on the bio section #251 it says that stratum germinativum is the deepest layer of the epidermis..however, in feralis notes the deepest layer is basale?

The stratum basale is also called the stratum germinativum

 

[DAT Destroyer]

In the destroyer on the bio section #251 it says that stratum germinativum is the deepest layer of the epidermis..however, in feralis notes the deepest layer is basale?

The stratum basale is also called the stratum germinativum

That is correct!

 

[bballjake300]

That is correct!

Thank you

 

[bballjake300]

Bio Question #24 asks for what process is common to both aerobic and anerobic organisms. The answer is glycolysis however, isn't the electron transport chain also common to both?

 

[DAT Destroyer]

Bio Question #24 asks for what process is common to both aerobic and anerobic organisms. The answer is glycolysis however, isn't the electron transport chain also common to both?

No. Glyclcolysis is always present. Citric Acid cycle is present only in some anaerobes, not in all.

 

[bballjake300]

No. Glyclcolysis is always present. Citric Acid cycle is present only in some anaerobes, not in all.

Thank you!

 

[bballjake300]

Bio Questions #104, In the explanation, it says xylem transport H20 and minerals up the stem while Phloem travels nutrients down the stem. I thought Phloem can travel up or down by source following sink?

 

[bballjake300]

Another question haha! #116 in Bio explanations says that Gluconeogensis happens primarily in the cytosol however, other sources say that it happens mainly in the liver?

 

[bballjake300]

So I know glycolysis produces 2 pyruvates so would that mean in Lactic Acid Fermentation 1 pyruvate produces 1 ATP to form lactate?

 

[DAT Destroyer]

Another question haha! #116 in Bio explanations says that Gluconeogensis happens primarily in the cytosol however, other sources say that it happens mainly in the liver?

It is referring to the cytosol of the cell.
Liver is the organ.
Destroyer is correct.
You answer would be correct if the question asked: In what Organ does Gluconeogenesis mainly occur?

Hope this helps

 

[bballjake300]

It is referring to the cytosol of the cell.
Liver is the organ.
Destroyer is correct.
You answer would be correct if the question asked: In what Organ does Gluconeogenesis mainly occur?

Hope this helps

Ah thank you! Makes sense

 

[DAT Destroyer]

Another question haha! #116 in Bio explanations says that Gluconeogensis happens primarily in the cytosol however, other sources say that it happens mainly in the liver?

You are almost correct. It can transport soluble Organic materials made by photosynthesis throughout the plant. It is a vascular tissue made for a long distance transport.
The reason it says "down the stem" is because it transports materials made by photosynthesis to the non-photosynthetic structures of the plant, mainly roots.

Hope this helps.

 

[bballjake300]

You are almost correct. It can transport soluble Organic materials made by photosynthesis throughout the plant. It is a vascular tissue made for a long distance transport.
The reason it says "down the stem" is because it transports materials made by photosynthesis to the non-photosynthetic structures of the plant, mainly roots.

Hope this helps.

Perfect, thank you!

 

[bballjake300]

I believe #501 in the bio solutions, the explanation is false.. because it says that the repressor(lactose) is involved with switching the operon OFF. I believe that lactose is involved with switching the operon ON because when you have lactose you would want to use the enzymes to break it down.

 

[molarbear8895]

Destroyer 2016 Ochem #231
The question asks to name the compound and the correct answer is 2-bromo-5,5-dimethylcyclohexanol.
I thought the constituents are numbered so that we get the lowest possible sum? Is this incorrect or am I missing something?

 

[DAT Destroyer]

Destroyer 2016 Ochem #231
The question asks to name the compound and the correct answer is 2-bromo-5,5-dimethylcyclohexanol.
I thought the constituents are numbered so that we get the lowest possible sum? Is this incorrect or am I missing something?

Start off by assigning # 1 to the alcohol group. Carbon #2 will be that carbon that has the first substituent, here it is bromine. This is the correct IUPAC rule,not the rule that you assumed. Carbon #1 is always assigned to the functional group. For further clarification see the David Klein text which does a wonderful job at explaining nomenclature.

Keep up the good work, that was a very good question.

Hope this helps.

Dr. Romano

 

[DAT Destroyer]

Yes, this is a typo. Lactose should not be there. Repressor is a protein involved in switching an Operator off. Thanks for bringing this to our intention.

Lactose is an inducer.

 

[molarbear8895]

Start off by assigning # 1 to the alcohol group. Carbon #2 will be that carbon that has the first substituent, here it is bromine. This is the correct IUPAC rule,not the rule that you assumed. Carbon #1 is always assigned to the functional group. For further clarification see the David Klein text which does a wonderful job at explaining nomenclature.

Keep up the good work, that was a very good question.

Hope this helps.

Dr. Romano

Thank you!

 

[Ineed2getin]

Dat destroyer biology question number 15. Why is B not the answer. isn't potassium inside the cell initially and the sodium ions are out of the cell?


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[bballjake300]

Dat destroyer biology question number 15. Why is B not the answer. isn't potassium inside the cell initially and the sodium ions are out of the cell?


Sent from my iPhone using SDN mobile

Sodium Potassium Pump is a type of active transport. Active transport is moving molecules against their gradient. (moving molecules from low to high concentration) So yes, potassium is initially inside the cell, but that's what we want which is to increase the concentration of potassium inside and sodium outside.

 

[DAT Destroyer]

Dat destroyer biology question number 15. Why is B not the answer. isn't potassium inside the cell initially and the sodium ions are out of the cell?


Sent from my iPhone using SDN mobile

You are correct. However, the question asks which answer is INCORRECT.
so, B is correct about Sodium Potassium ATPase 3 Sodiums are pumped out for every 2 Potassiums pumped in.

Hope this helps.

 

[molarbear8895]

OCHEM 2016 Destroyer #63

The question asks for the number of isomers ( both constitutional and stereoisomers) for a dimethyl cyclopentane.
The answer is 6 and in the key it shows the stereoisomers, although wouldn't there be much more because we are including constitutional isomers? like noncyclic with a pie bond.

Are these counting isomer questions common on the DAT? It takes me a long time to draw out all the possible conformations.

 

[DAT Destroyer]

OCHEM 2016 Destroyer #63
The question asks for the number of isomers ( both constitutional and stereoisomers) for a dimethyl cyclopentane.
The answer is 6 and in the key it shows the stereoisomers, although wouldn't there be much more because we are including constitutional isomers? like noncyclic with a pie bond.

Are these counting isomer questions common on the DAT? It takes me a long time to draw out all the possible conformations.

Anything on the DAT is fair game, and although a challenging question , it represents a garden-variety organic chemistry question. For this question.....I wanted you to write all isomers including stereoisomers. I need to specify that all isomers requested have methyl groups and a cyclopentane ring system only. If not...then an ethyl cyclopentane could have been drawn giving 7 isomers all together. If we counted all possible isomers with this molecular formula....yes , indeed, we would have many many isomers !!!! Thus ,I put a restriction on the answer. This problem will be a great challenge because it demands you to recognize enantiomeric relationships and meso compounds .

Hope this helps.

Dr. Jim Romano

 

[dentalpredent2016]

Does the fertilization membrane form in pretty much all animals? bio #247 on 2016 specifically says sea urchins, but i was just wondering if they could've said other species. thank you

 

[elemental951]

GC Destroyer question
73. Which of the below forces are responsible for CO2 Water solubility?
The correct answer is Dipole/induced dipole attraction
but I'm confused about the difference between Dipole/induced dipole and london forces?
They sound like they are the same thing and having to do with the arrangement of electrons

 

[DAT Destroyer]

GC Destroyer question
73. Which of the below forces are responsible for CO2 Water solubility?
The correct answer is Dipole/induced dipole attraction
but I'm confused about the difference between Dipole/induced dipole and london forces?
They sound like they are the same thing and having to do with the arrangement of electrons

Dipole-induced dipole interactions occur when a polar molecule interacts with a non-polar molecule. There is a greater distortion of the electron cloud than that seen in a simple Van Der Waals interaction.

Van Der Waals Interactions occur when nonpolar molecules and polar molecules interact with each other, but is often very very weak.

Hope this helps

Dr. Romano

 

[Kstar007]

Gen. Chem Question 151

Why couldn't Ag further react since it is a cation of a weak base, and then increasing the pH would remove H+??

 

[zyzzbruh]

2016 General Chemistry #344

Why does it say Cobalt has 2 valence electrons? I was under the impression that we include the d subshell electrons as valence as long as the block is not filled. Looking at the electron configuration: 3s^2 3p^6 4s^2 3d^7 wouldn't Cobalt have 9 valence shell electrons?

 

[DAT Destroyer]

Gen. Chem Question 151

Why couldn't Ag further react since it is a cation of a weak base, and then increasing the pH would remove H+??

Ag+ would react in an acid base ( Lewis ) reaction if NH3 was the solvent to form a complex ion Ag (NH3)2 +. However water does NOT form an appreciable reaction , nor form a complex ion. The complex with Ammonia is stable.....water it is not. Great question,,,,,,I am glad you are considering other possibilities.

Hope this helps

Dr. Romano

 

[DAT Destroyer]

2016 General Chemistry #344

Why does it say Cobalt has 2 valence electrons? I was under the impression that we include the d subshell electrons as valence as long as the block is not filled. Looking at the electron configuration: 3s^2 3p^6 4s^2 3d^7 wouldn't Cobalt have 9 valence shell electrons?

WOW !!! This is an awesome question .

In General Chemistry, we look at the energy level that has the highest n quantum number...here it is 4...thus we say that there are 2 valence electrons, since two reside in the 4s sublevel. Now...the organo-metallic chemist would agree with you and say 9, since the energy levels of the 4s are 3d are quite close.

In the organic chemistry text by Dr. Marc Loudon of Purdue University, he makes an excellent case and explains this in greater detail. The bottom line is this......In General Chemistry......say the answer is 2....and stick to the formal definition of valence.

In advanced Organic Chemistry, or Quantum Chemistry we would say 9. Thanks for an awesome question.......


Hope this helps.

Dr. Romano

 

[bballjake300]

WOW !!! This is an awesome question .

In General Chemistry, we look at the energy level that has the highest n quantum number...here it is 4...thus we say that there are 2 valence electrons, since two reside in the 4s sublevel. Now...the organo-metallic chemist would agree with you and say 9, since the energy levels of the 4s are 3d are quite close.

In the organic chemistry text by Dr. Marc Loudon of Purdue University, he makes an excellent case and explains this in greater detail. The bottom line is this......In General Chemistry......say the answer is 2....and stick to the formal definition of valence.

In advanced Organic Chemistry, or Quantum Chemistry we would say 9. Thanks for an awesome question.......


Hope this helps.

Dr. Romano

So all 3d transition metals have 2 valence electrons? except for copper and chromium which have 1?

 

[dentalpredent2016]

For bio #356, it gives the frequency of the allelle for a recessive trait. Since it's the allele frequency, doesn't it equal q? Wouldn't q^2 be the frequency of the trait itself, not the allele's?

 

[DAT Destroyer]

For bio #356, it gives the frequency of the allelle for a recessive trait. Since it's the allele frequency, doesn't it equal q? Wouldn't q^2 be the frequency of the trait itself, not the allele's?

For any ordinary problem you would be correct. However, this question is tricky.
It is asking for the allele frequency in individuals suffering from Cystoc fibrosis, which is a homozygous recessive. Therefore, sonce we are only assuming homozygous individuals 1/2500, it is q^2.

Hope this helps.

 

[Ineed2getin]

Dat destroyer biology question 172.
Does the autonomic nervous system include both motor and sensory neurons? Or does it not have any motor neurons at all?


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[DAT Destroyer]

Dat destroyer biology question 172.
Does the autonomic nervous system include both motor and sensory neurons? Or does it not have any motor neurons at all?


Sent from my iPhone using SDN mobile

It includes both motor and sensory neurons.