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Chemistry MCQ thread...

Omar Haider

Omar Haider

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crazytaylorfanXD said:
Can someone help me with a few questions from :
JUN 08 QS31
NOV 08 QS 2 , 31
JUN 11 QS 24 , 31
Click to expand...

Q31: All you have to do is write down the combustion reactions for each compound. I'll write them below.

C2H5OH + 3O2 = 2CO2 + 3H20

As you can see, for this reaction, 3 moles of O2 are needed so this is incorrect and we know that since 1 is incorrect, the answer must be C.

____________________________________________________________________________________________

Q2:
num. of mole of CS2 = 10/24000 = 4.17 x 10^-4 mole
number of mole of oxygen needed = 3 x 4.17 x 10^-4 = 1.25 x 10^-3 mole
vol of oxygen needed = 1.25 x 10^-3 x 24000 = 30cm3
- so we have 20cm3 of unreacted oxygen

volume of CO2 produced = 10cm3
volume of SO2 produced = 20Cm3
- so volume of gas after burning is 10 + 20 + 20 = 50cm3

when added with NaOH, SO2 will react with NaOH , SO2 + NaOH -> Na2SO3 + H2O, no gas
CO2 + NaOH -> Na2CO3 + H2O

so all we have left at the end is the 20cm3 of oxygen.

ans : C
(copy/pasted from previous forum)

Q31: Statement 1 is true because the hydrogen's of Kevlar are attached to Nitrogen, which is very polar element and thus can make hydrogen bonds with other N-H groups.
Statement 2 is true because the question mentions that Kevlar is lighter, and you can check this by adding up masses.
Statement 3 is false because the molecule does have a dipole. There is a big electronegativity difference between Nitrogen and Hydrogen so the Nitrogen gets a partial negative charge and the Hydrogen, a partial positive charge, and this is a permanent dipole.


Which variant are you referring to for Summer 2011?
 
crazytaylorfanXD

crazytaylorfanXD

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Omar Haider said:
Q31: All you have to do is write down the combustion reactions for each compound. I'll write them below.

C2H5OH + 3O2 = 2CO2 + 3H20

As you can see, for this reaction, 3 moles of O2 are needed so this is incorrect and we know that since 1 is incorrect, the answer must be C.

____________________________________________________________________________________________

Q2:
num. of mole of CS2 = 10/24000 = 4.17 x 10^-4 mole
number of mole of oxygen needed = 3 x 4.17 x 10^-4 = 1.25 x 10^-3 mole
vol of oxygen needed = 1.25 x 10^-3 x 24000 = 30cm3
- so we have 20cm3 of unreacted oxygen

volume of CO2 produced = 10cm3
volume of SO2 produced = 20Cm3
- so volume of gas after burning is 10 + 20 + 20 = 50cm3

when added with NaOH, SO2 will react with NaOH , SO2 + NaOH -> Na2SO3 + H2O, no gas
CO2 + NaOH -> Na2CO3 + H2O

so all we have left at the end is the 20cm3 of oxygen.

ans : C
(copy/pasted from previous forum)

Q31: Statement 1 is true because the hydrogen's of Kevlar are attached to Nitrogen, which is very polar element and thus can make hydrogen bonds with other N-H groups.
Statement 2 is true because the question mentions that Kevlar is lighter, and you can check this by adding up masses.
Statement 3 is false because the molecule does have a dipole. There is a big electronegativity difference between Nitrogen and Hydrogen so the Nitrogen gets a partial negative charge and the Hydrogen, a partial positive charge, and this is a permanent dipole.


Which variant are you referring to for Summer 2011?
Click to expand...
omg thanks :)
also i meant to write JUN11 P11
 
A

ashcull14

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SomeStudent

SomeStudent

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Love Islam said:
Q28: Ans: C

It is an Aldehyde and it will get Oxidised by KMnO4 and it also reacts with 2,4 DNP to gve orange colour, Whereas in option A and D it will decolorize KMnO4 but will not react with 2,4 DNP. And Option B. is a Ketone, it doesn’t get oxidized, but it only reacts with 2,4 DNP!

Q39: Ans: C

Because it posses 3 Chiral centre so First is wrong, the 2 and 3 has to be correct!

Q9: Ans: B

The oxidation no. of S in SO3^-2 is +4 and on other side it is +6. So Oxidation No. increased by 2 so it means the metal in it, its oxidation will decrease by 2, but the mole of Metal: Sulphite (2:1) so total increase 2/2= +1, so before it was +3 but now it has changed by 1, so the Oxidation No. is 3-1 = +2

Q20: Ans: C

Because it is an Optical isomer it has same 3-D dimensional structure!
Click to expand...
Love Islam said:
Even If speed increases, The energy increases but it might not be sufficient to overcome Ea! but if the molecules posses enough energy to overcome Ea, then only the rate will double,
I hope you understand!
Click to expand...

Thank you heaps!!! :)
I am still confused abT that SO3 one.. why did you divide 2/2??
 
dumb human

dumb human

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Zishi said:
Hi people,

How about posting your problems in MCQS in this thread? This way many people will benefit from your problems(as all the tough MCQs, etc will be there in just on thread). :)

By the way you may also post your confusions in ANY topic. We'll try to help you clearing your concepts. :good:
Click to expand...
Chemistry June 2013, Paper 1_2 Question 31?? y A?
 
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