question from OAT sample test, need help

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.

depot123

Full Member
10+ Year Member
Joined
Jan 7, 2011
Messages
29
Reaction score
0
I need help with some explanation with question from oat sample

1. according to the second law of thermodynamics
C any system isolated from an energy sources tends to decrease in entropy
E. any system isolated from an energy source tends toward tis least ordered state

ans is E (i choose c)

2. the muscle cells of the human heart are primarily nourished by
E. blood delivered by the ductus arteriosus

43 for the reaction between A and B to form C it is found that when one combines 0.6 moles of a with 0.6 moles of B, all of the b reacts, 0.2 moles of A remain unreacted and 0.4 moles of C are produced. What is the balance equation for this reaction?

Ans is E 2A + 3B -> 2C
but i think the answer is wrong. I got my answer C 3A + 2B -> 2C

44 if the mass percent of oxygen in a nitrogen-oxygen compound is known, give the mass percent of oxygen, all of the following are needed to determine the molecular formula of a nitrogen-oxygen compound except one.
A. atomic mass of nitrogen
B. atomic mass of oxygen
C. avogadro's number
D. empirical formula
E. molar mass of the compound
Ans : D

have no ideas on this

56. AgCl (s) + 2NH3 ->Ag(NH3)2+ (ag) + Cl- (ag), the equilibrium constant K 4X10^-3, which of the following statement is true? (Ksp for AgCl is 1X10^-10)
A the addition of NH3 decrease the solubility of AgCl
B AgCl is more soluble in aqueous NH3 than in water
C AgCl is more soluble in aqueous solution containing Cl- than in water
D AgCl is less soluble in aqueous NH3 than in water

73
it is believe that an unlabeled bottle containing an unknown liqueid is either 2-pentatnone or 3 - pentanone. What is the best method to distinguish?
A mass spectroscopy
B IR spectroscopy
C 13C NMR spectroscopy
D thin layer chromatography
E melting point determination
ANS C (i choose A)

74
Can someone explain why it is A?
https://www.ada.org/oat/oat_sample_test.pdf


93. what is the hybridization of a nitrogen atom if it forms two alpha and two pi bond?
C sp3
i don't get this, is answer wrong

95
which functional group can act as both a bronsted acid and bronsted base?
B alcohol
i choose D amide
why?

thanks for all your help.


ANS: B



help? please

Members don't see this ad.
 
And this is why ADEA should proof-read their tests:

http://forums.studentdoctor.net/showthread.php?t=605494

That should answer most if not all of your questions.

I was editing the post to give the other answers and the SDN site went into maintenance:

1) E is correct since least ordered state = more disorder = more entropy (which is what the 2nd law says)

2) No idea but I'll believe them sounds right I guess.

43) Your answer is wrong because in your answer you have A being the limiting reagent (.2 mol equivalents) but we know that all of B has been used so B has to be the limiting reagent so its 2A + 3B ---> 2C

44) Look above

56) Well given the K for this reaction is much bigger (i.e. more likely to happen) I'd say its more soluble...I might be wrong about this though. Forgot my Ksp questions

73) Mass spec would be the right answer I feel since 2 pentanone would split into methyl, propyl and carbonyl. 3 pentanone would be ethyl, ethyl and carbonyl. C-NMR wouldn't reveal much I feel.

74) I remember that question even when I took it. I don't know what mechanism they are shooting for. I know even less how OEt becomes OH but that is why ADEA makes the best mistake proof tests.

93) Above

95) Amides don't readily donate the H+ always if I remember correctly. OH does. While both Amides and OH can readily accept protons. So I'd have gone with OH over amides.
 
Last edited:
A little bit on the reply but I'll just attempt to answer some for those who needs it in the future.

43) Since all of B is used up and only 0.2 moles of A is left, that means the product C has to also be 0.2 moles. Therefore, based on stoichiometry, the coefficients of A and C have to be the same. 2A + 3B ---> 2C. So if A is 0.2 moles, plugging in will give 0.4 moles for A, which is the same if you plug in 0.2 moles for C, which is what is produced.

44) C (Avogrado number) should be the correct answer, not D (Empirical formula). We need to find the number of moles to determine the empirical formula, and from the empirical formula use a multiplier to find the molecular formula. Avogrado deals with using molecules so it is not needed here.

56) Ans B. Two ways of seeing this. AgCl is highly insoluble in water, but when mix with aq. NH3, it forms a complex ion, Ag(NH3)2+ (ag), which is highly soluble. Another way is comparing the given Keq to the Ksp. Since Keq is for the formation of Ag(NH3)2+ (ag), and Keq < Ksp, the solubility should be higher in NH3.

73. Ans C. 13C NMR spectroscopy can be used to determine the number of different carbons in the compound. 2-pentanone has 5 different carbons and 3-pentanone has 3 different carbons.

93) sp3 is wrong anwer. It should be sp. Consider the case of azide, R-N=N=N. The middle N has 2 sigma and 2 pi bonds. There are 2 electron domains surrounding that N (double or triple bonds are still counted as 1 electron domain), 1 on each side. sp has 2 electron domain (s1p1 , add up the exponents), sp3 has 4 electron domain.

95) -OH is an amphoteric specie, in that it can act as a Bronsted base or acid. Bronsted base will accept protons, and acids will donate protons. In the case of NaOH, it acts as a base since NaOH dissociates completely to become Na+ and -OH ions and can accept a proton to become water. In the case of metal hydroxide, Al(OH)3, some of the electron density on O will shift towards Al, allowing the proton on OH to dissociate away or be donated.
 
Top