Chemistry MCQ thread...

[hassam]

Bye...i guess this the biggest thread in XPF history

 

[RafaySid]

well need help on this question......how i ll figure out valency of Cl in CrO2Cl2....???

Ans is D. Cl mostly has an oxidation state of -1, like oxygen has -2, because they are highly electronegative atoms as the series goes F O N Cl Br... In this case both O and Cl 'pull' electrons away from Cr so they both have negative oxidation numbers.

 

[Ash1994]

A typical solid fertiliser for use with household plants and shrubs contains the elements N, P, and
K in the ratio of 15g : 30g :15g per 100 g of fertiliser. The recommended usage of fertiliser is 14g
of fertiliser per 5 dm3
of water.
What is the concentration of nitrogen atoms in this solution?
A 0.03mol dm–3
B 0.05mol dm–3
C 0.42mol dm–3
D 0.75mol dm–3

 

[Mobeen]

SO2Cl2...how to work valency of sulfur in this compound

put all the valencies and equate them to zero .. and to find the valency of sulfur put it as x .. :
x + (2*-2) + (2*-1) = 0
x -4 -2 = 0
x = 6..

 

[Saturation]

Number 35, I get that MgO and and BaO will form, but won't the MgO formed react with the NO2 (acidic oxide), forming magnesium nitrate? Please explain!
The answers B btw.

http://www.xtremepapers.me/CIE/Internat ... 7_qp_1.pdf

Ba is more electropositive than Mg, hence Mg cannot displace Ba.

But doesn't the NO2 gas produced react with the MgO?

 

[Mobeen]

A typical solid fertiliser for use with household plants and shrubs contains the elements N, P, and
K in the ratio of 15g : 30g :15g per 100 g of fertiliser. The recommended usage of fertiliser is 14g
of fertiliser per 5 dm3
of water.
What is the concentration of nitrogen atoms in this solution?
A 0.03mol dm–3
B 0.05mol dm–3
C 0.42mol dm–3
D 0.75mol dm–3

mass of nitrogen in 14 g = 15/100 * 14 = 2.1
moles of nitrogen = 2.1/14 = 0.15
conc in 5 dm3 = 0.15/5 = 0.03 mol dm-3

 

[hassam]

0.200 mol of a hydrocarbon undergo complete combustion to give 35.2 g of carbon dioxide and
14.4 g of water as the only products.
What is the molecular formula of the hydrocarbon?
A C2H4 B C2H6 C C4H4 D C4H8

 

[hassam]

its D ryt?/

 

[srukhan]

Guys, my doubt.. It frigging driving me insane:
Nov 2005, Q12 (ans: D)
Nov 2006, Q9 (ans: C)

 

[AayushR]

Chill.
Dnt go nuts, it won't help.

 

[zwitterion7]

Which isomer of C4H10O forms three alkenes on dehydration?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

Can someone please explain how to reach the answer?

 

[diwash]

Thank you guys for the thread....
learned many things and also shared many things...
all the best to all of u
may all of us get 35+

 

[airborne1944]

Which isomer of C4H10O forms three alkenes on dehydration?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

Can someone please explain how to reach the answer?

Think about cis-trans isomer.

 

[girlscampisra]

Nov 2006, Q9 (ans: C)


Solution:
-283 + delta H = 44 + (-286)
delta H = 41

take 44 positive cause H20 gas to liquid is -44
so liquid to gas would be +44 !!

 

[ShootingStar]

Question! Please explain. Answer is B

 

[diwash]

@shootingstar..look there are 9 carbon double bonding in the original molecule. and after the conversion there are total of 4 carbon double bond remaining( 2 from 1st reidue and 2 from 2nd and 3rd resiude). this means 5 double bond has been removed. As we know one carbon double bond is removed byone hydrogen molecule, 5 carbon double bond is removed by 5 hydrogen molecules.

 

[zwitterion7]

Which isomer of C4H10O forms three alkenes on dehydration?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

Can someone please explain how to reach the answer?

Think about cis-trans isomer.

I dont get it. Could you explain further, please.

 

[ShootingStar]

@shootingstar..look there are 9 carbon double bonding in the original molecule. and after the conversion there are total of 4 carbon double bond remaining( 2 from 1st reidue and 2 from 2nd and 3rd resiude). this means 5 double bond has been removed. As we know one carbon double bond is removed byone hydrogen molecule, 5 carbon double bond is removed by 5 hydrogen molecules.

Thanks alot!!! great explanation! :Bravo:

 

[Abdulrab]

thanks !!

 

[diwash]

Which isomer of C4H10O forms three alkenes on dehydration?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

Can someone please explain how to reach the answer?

Think about cis-trans isomer.

I dont get it. Could you explain further, please.

look first of all draw urs a stucture of butan2ol... dehydrate it u will get either..CH3CH2CH=CH2 or CH3CH=CHCH3( look carefully..this is cis isomer ....so it also can have trans isomer) ..so there are three alkenes that can be made.