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Topic: exam questions I missed and still don't know how to do  (Read 17408 times)

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integral0

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exam questions I missed and still don't know how to do
« on: December 11, 2004, 03:06:56 PM »
1. Based on Molecular orbital theory, the bond order of the O-O bond in the O2+ ion is ______ and the ion is _____.

A) 1/2 paramagnetic  B) 1/2, diamagnetic  C) 2 1/2, paramagnetic  D) 2 1/2 diamagnetic


2. Calculate the electron affinity for the formation of the hydride ion from the following information:

H(g) + e- -> H- (g)                    ?

1/2H2(g) -> H(g)                  217.9 kj/mol

Na(s) -> Na(g)                      107.3 kj/mol

Na(g) -> Na+(g) + e-              495.8 Kj/mol

Na(s) + 1/2H2(g) -> NaH(s)    -60 Kj/mol

NaH(s) -> Na+ (g) + H-(g)      +810kj/mol

A) -70.1 kj/mol  B) -50.1 kj/mol  C) -1632 Kj/mol  D) -816 kj/mol


3. A 255 mL round-bottom flask is weighed and found to have a mass of 114.85 g.  A few milliliters of an easily vaporized liquid are added to the flask and the flask is immersed in a boiling water bath.  All of the liquid vaporizes at the boiling temperature of water, filling the flask with vapor.  When allof the liquid has vaporized,  the flask is removed from the bath, cooled, dried, and reweighed.  The new mass of the flask and the condensed vapor is 115.23 g.  Which of the following compounds could the liquid be?  (Assume the ambient pressure of 1 atm.)

A) C4H10  B)C3H7OH  C)C2H6  D)C2H5OH


4. The reaction below is used to produce methanol:

CO(g) + 2H2(g) -> CH3OH (g)  Change of Hrnx = -128 kj

Calculate the C-H bond energy give the following data:

C triple bond O  1072 kj/mol
H single bond H  436 kj/mol
C single bond O  358 kj/mol
O single H          463 kj/mol

A) 417      B)1251  C)815    D)272


I think I know what I did wrong now . . . I think I left the answer in Kj/mol when it was just actually asking for the answer in Kj (energy). . .  not sure though


5. What type of bond produces a charge cloud with a nodal plane containing the bond axis?

a) sigma    b) pi    c)sigma antibonding      d) pi antibonding


6.Carol and Joe have a brother named Mike,  Mike has a trantula that keeps getting loose.  Carol and Joe decide to rid themselves of the creature once and for all by sending it for a ride with a helium balloon.  The spider weighs 3 oz and we ignore the weight of the balloon itself.  If we assume STP and that 4.0 g of He gas will lift 6.0 g of matter, what must the volume (in L) of their balloon filled with He be to send Mr. Tarantual for a ride?  (1 oz = 28.35g)

A) 22.4    B) 227140  C) 317.7  D)53.16.

integral0

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Re:exam questions I missed and still don't know how to do
« Reply #1 on: December 16, 2004, 06:07:30 PM »
Since no one has cared to attempt these, I'll do what I can with my own problems!

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5. Its D(antibonding) . . . you just gotta know

6) you take the oz of the spider and switch it to grams . . . then you divide it by the ratio . . . 4gHe to lift 6g of matter . . . you divide the spiders mass in grams by the lift (6g) . . . to give you 14.18 . . . this number is the number you need to multiply 4 g He by to find out how many g of helium you need to put into the balloon.  After you get that number . ..  you then multiply that number by Helium's molar mass to get the amount of moles of Helium you need . . . then take the amount of Helium and multiply by STP (22.4L) to find the amount of liters which is

317 L which is the answer

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i'm still solving the others, help would be appreciated!

Offline jdurg

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Re:exam questions I missed and still don't know how to do
« Reply #2 on: December 16, 2004, 08:46:04 PM »
For number 2, you simply have to add all the equations together in the proper orientation so that all products and reactants cancel out except for H(g) + e- -> H-(g).  Just remember that if a value is given for a reaction in one direction, if you flip the reaction around in the reverse direction you have to change the sign from positive to negative.  (For example, if you have Na(s) -> Na(g) = 107.3 kj/mol, Na(g) -> Na(s) = -107.3 kj/mol.)
"A real fart is beefy, has a density greater than or equal to the air surrounding it, consists

integral0

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Re:exam questions I missed and still don't know how to do
« Reply #3 on: December 17, 2004, 03:00:29 PM »
thanks Jdurg.  

Do you know how to do number 3?   I'm stuck on that one.

integral0

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Re:exam questions I missed and still don't know how to do
« Reply #4 on: December 17, 2004, 03:03:32 PM »
4. The reaction below is used to produce methanol:

CO(g) + 2H2(g) -> CH3OH (g)  Change of Hrnx = -128 kj

Calculate the C-H bond energy give the following data:

C triple bond O  1072 kj/mol
H single bond H  436 kj/mol
C single bond O  358 kj/mol
O single H          463 kj/mol

A) 417      B)1251  C)815    D)272


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I solved this one the other day.

Basically, its very straightforward.  I just forgot to include an extra CO bond and that did it for me.  The answer is 417...

integral0

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Re:exam questions I missed and still don't know how to do
« Reply #5 on: December 17, 2004, 03:18:48 PM »
just solved number 3!  

you have pressure (1 atm)  volume (225ml) R (constant) and T (373K) find n, number of moles
do 115.23 - 114.85 and you have grams
then you have grams/mol.. turn into kg/mol then find which one it matches up with
i think its D

integral0

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Re:exam questions I missed and still don't know how to do
« Reply #6 on: December 18, 2004, 12:26:55 PM »
Can someone explain to me this question?

Which of the following three sets consists of atoms or ions with the same electron configuration in the ground state?

(I) O2-, Ne, Mg2+
(II) Ni, Cu+, Zn2+
(III) Hg, Tl+, Pb2+

A) all but II

A is the answer . . . but I don't understand why Ni, Cu+, and Zn 2+ are not the same electron configuration in the ground state?  Can anyone lend me some knowledge?

integral0

  • Guest
Re:exam questions I missed and still don't know how to do
« Reply #7 on: December 18, 2004, 12:51:26 PM »
for Ni, the electron config is 4s23d8 and for Zn2+ it's also that but Cu is an exception, so it's electron configuration is 4s13d10, but when it's Cu+ it's just 4s13d9
so because it's an exception, it's different

sorry, when i figure things out, I answer my own questions, Hey! Its part of learning!
« Last Edit: December 18, 2004, 12:51:52 PM by integral0 »

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