couple of bio questions

[vixen]

couple of bio questions:

1) Which is an example of an agonistic display?

A) courtship behavior
B) Dog baring its teeth and erecting its ear
C) A dog attacking and injuring another dog
D) waggle dances of honeybees to indicate the direction of food
E) scent-oriented retrieval by dogs

The answer is B. I think the wording in this question sucks....the other answers arent right, but B makes it seem like an antagonistic display....or am I missing something?

2) Ok, this question, its kind of stupid, but i just want to make sure i'm doing it the right way:

How many genetically different gametes can be formed by a mouse that is genotypically AABbCc (assume no linkage)

A) 4 (I picked this, the right answer, cause I thought you could only have A (1) then B or b (2) then C or c (2)....so 1x2x2=4. Am I getting the answer the right way or was that just a lucky guess?

Thanks

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[groundhog]

I don't know, but as far as I'm concerned, some of the courship behaviors that I've observed were pure agony to behold.

 

[vixen]

1) The cattle egret concentrates its feeding where grazing cattle flush insects from the vegetation. This is an example of:

The answer is commensalism...I guessed for this because I didn't comprehend what the heck they were talking about! Is is just me or is the wording kind of weird in that?

2)If 1 mol of H2 and 1 mol of O2 are mixed and allowed to react according to the question: 2H2 + O2 ----> 2H2O, the maximum number of moles of H2O that could be produced is:

the answer was 1. I did this kind of logically, but is there a better way?

3) For the equilibrium (NH4)3PO4 <==>3NH34+ +PO4^3-, the solubility product expression (Ksp) is:

the answer is [NH4+]^3[PO4^3-]. Just checking why do you not put the reactant on the bottom here in your answer? Are you supposed to only have ions in the Ksp? This might be a stupid question Im asking!

4)Which of the following cmpds contain 42% Cl and 57%oxygen by weight?

HCl, HClO, ClO2, HClO3, HClO4? the answer is HCl03. I did it by process of elimination...is there a faster way?

5) The equilibrium for the following rxn:

Cl2 (g) + PCl3 <====> PCl5 (g) delta H= -88 kJ/mol
can be shifted to the right by:

A) decreasing the volume
B) decreasing the pressure
C) increasing the temp
D) adding a catalyst
E) emoving chlorine from the container

the answer is A. I thought I should use PV=nRT here, but I dont think it helps....why A and not B??

Also, just checking, ionic solids dont conduct electricity, right? And covalent don't conduct as liquids or in aqueous.

 

[vixen]

Originally posted by groundhog
I don't know, but as far as I'm concerned, some of the courship behaviors that I've observed were pure agony to behold.

thanks for the breath of fresh air!

 

[vixen]

When an oxygen nucleus containing nine neutrons emits an alpha particle, the other product of the balanced rxn:

O (17 on top, 8 on bottom) -------> He (4 on top, 2 on bottom) + ____ is:


The answer is C (13 on top, 6 on bottom)....but Al (13 on top, 6 on bottom) was also a choice.


I guessed the carbon one and it was right, but I don't know why....why carbon and not aluminum....the rest of the choices were out, they didn't add up.

 

[UBTom]

Hi Vixen,

Several of the above questions I can answer...

1) The first question with the dog: "agonist" to me means something to do with epinephrine (which is an agonist hormone, that whole "fight or flight" thing). The Dog baring its teeth and erecting its ear is going into that "fight or flight" thing.

2) The mouse gametes: Yes, that's how you calculate the permutations.

3) Commensalism: It means a relationship in which one organism benefits from the presence of the other, but the other neither benefits nor gets harmed in the relationship.

4) 1 mol of H2 and 1 mol of O2: No faster way to do this problem except to realize from the chemical formula "H2O" the correct proportions of reactants.

5) Which compounds contain by weight 42% Cl and 57% O: Best way to do it is look up all the weights in the periodic table (I'm pretty sure one will be provided during a DAT exam).

6) The equilibrium of the Cl2 + PCl3 --> PCl5 can be shifted to the right by decreasing the volume because when you decrease volume, you increase pressure. Increase pressure, and particles of reactants are brought in closer to each other, and facilitates formation of product.

7) Aluminum is not a choice at all. Its atomic weight is 27 and atomic number is 13 (13 protons). It is physically impossible for an Oxygen isotope-17 (i.e. 17 atomic weight and 8 protons) to decay to that.

HTH!

 

[vixen]

Thanks UB Tom!!!! Makes sense!

Hey just saw more of your answers, thanks...you remember a lot from undergrad? Impressive!

 

[vixen]

I apologize for all these questions, but this one sample test has no explanations! errrr

1) How many moles of AgIO3 (Ksp=3.1 x 10^-8) will dissolve in one liter of a 10^-5M soln of NaIO3?

the answer is ([3.1x10^-8]^1/2) - (10^-5). How'd they get that?

2) what is the standard Enthalpy change for the following rxn:

2SO2 + O2 ---> 2SO3

substance delta Hf (kJ/mol)
SO2 -297
O2 0
SO3 -396

The answer is -198 kJ/mol. It seems so easy, but why is that the answer?

 

[UBTom]

Those last two has me stumped. Trust me when I say I dont' remember much from my undergrad days! Glad to be of some help though.

 

[portlander]

2) what is the standard Enthalpy change for the following rxn:

2SO2 + O2 ---> 2SO3

substance delta Hf (kJ/mol)
SO2 -297
O2 0
SO3 -396

The answer is -198 kJ/mol. It seems so easy, but why is that the answer?

It has something to do with Hess's law...enthalpies are addative. Just look at which compounds are on which side of the equations and assign a direction (which enthalpies will be positive and which ones will be negative). For example, SO3 is on the product side, it is being formed, therefore it's delta Hf will be 2(moles)x(-396Kj/mol)

Just add them all up and you get:

(2moles SO2)(+297 kJ/mol)+(1moles O2)(0 kJ/mol)+(2moles SO3)(-396 kJ/mol)

=~ -200kJ/mol

I hope that wasn't confusing!

Good luck!

 

[ALI]

hi vixen
the AgIO3 solubility problem seems weird to me. Could you check the answer or the question again? The anwser does not make sense to me. The solution's unit does not correspond to the question.

can some one solve this problem
thanks

 

[vixen]

ALI, I just double checked the question and answer and its what I wrote. p.s. remember that ^1/2 means square root.


Still don't know how they got that. I don't understand why they use square root at all in this?

 

[vixen]

I'm gonna post a couple of organic questions before I go to the library:

1) Which of the following cmpds is not capable of hydrogen bonding?

A) C4H11N
B) C4H9NO
C) C4H7F3
D) C4H8O2
E) C4H10O

The answer is C. I thought of "FON"....and since all of them have F, O or N, I didn't know which one DID NOT H-bond...anyone know why?

2) Which cmpd would not be expected to react w/sodium metal?
A) CH3OCH3
B) CH3CH2OH
C) CH3COOH
D) C6H5OH
E) CH3I

The answer is A. Is this becaue its an ether, which really wont react with the Na, and then rest are more likely to react w/Na?

3) Na+ is NOT an electrophile because:

A) It does not readily form a covalent bond with a nucleophile
B) It is an ion
C) It has a noble gas configuration
D) It has an empty orbital
E) It is electron deficient

The answer is A, anyone know why?


4) Choose the letter corresponding to the INCORRECT completion. In the nitration of benzene by conc H2SO4 and conc HNO3:

A) the rxn is irreversible
B) the rate determining step is the removal of H+ from the intermediate
C) the attacking electrophile is NO2+
D) The second nitro group enters the benzene ring meta to the first nitro group
E) If the conc H2SO4 is replaced by some other strong acid such as HF, the rxn will still proceed at a similar rate.

Answer is B. If there's an intermediate, it means its SN1 rxn right? Anyone know a good way to figure out if a rxn is SN1, SN2, E1 or E2?


Also, it has a question with stability and it says in the answer that 2,2-dimethyl butene is more stable than cyclohexene, does anyone know why?

Thanks!

 

[Dentalstu02]

hey seema
Where do you get these questions from? They are not from kaplan, or topscore, right? Just curious...

 

[vixen]

they're ALL from a kaplan free test I took at their testing center....luckily there are NO explanations! Talk about annoying...but I wanted to still go over them and understand them....hope i'm not bothering you with these questions!

 

[Dentalstu02]

No not at all. I was just wondering where they were from because I havent seen them before. If anything, they are good practice questions for those of us taking the exam soon!

 

[vixen]

bumping these up again...

adding one more question to it:

Which of the following alkenes will react with Bromine to yield a meso cmpd?

A) trans-2-butene
B) 1-butene
C) cis-2-pentene
D) 2,3-dimethyl-2-butene
E) cis-2-butene

answer is A. How do you get a meso cmpd from that? I dont see how there could be symmetry if they are trans?