Chemistry MCQ?

[Ash1994]

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

I got CH2 empirical formula buh stuck on molecular as they din give us the Mr or mass of Hydrocarbon?

 

[soul1]

CxHy + O2 --> CO2 + H2O

number of moles of CO2: 35.2g / (12+16+16)gmol-1
=0.8 mol.

Same number for H2O.

CxHy has 0.2 mol, meaning 4 less (ratio) than CO2 ad H2O, so:

CxHy + O2 --> 4CO2 + 4H2O

Balancing the Cs, and following the molar ratio, x is 4, and y is 8. The O2 reactant can be balanced to make it have 6, therefore:

C4H8 + 6O2 --> 4CO2 + 4H20

Answer is D. Butene.

 

[DANGERBP]

CxHy + O2 --> CO2 + H2O

number of moles of CO2: 35.2g / (12+16+16)gmol-1
=0.8 mol.

Same number for H2O.

CxHy has 0.2 mol, meaning 4 less (ratio) than CO2 ad H2O, so:

CxHy + O2 --> 4CO2 + 4H2O

Balancing the Cs, and following the molar ratio, x is 4, and y is 8. The O2 reactant can be balanced to make it have 6, therefore:

C4H8 + 6O2 --> 4CO2 + 4H20

Answer is D. Butene.

hey but if tht n mcq wont it take like much time ??

 

[mujtabashahnawaz]

You would have to practice such questions so that you can cope with them within 1.5 min. These type questions usually take time

 

[soul1]

True. Practicing these calculations will make you answer the question in about a minute. And it's not Paper 2 or 4, so you don't ACTUALLY have to write down any working. Skip a few steps (do them mentally), and only write things you may confuse like the number of moles.

 

[smartangel]

please tell me in this question.. how is nitrogen undergoing a redox reaction??http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Q35 of this paper

 

[soul1]

Well, N is reduced from +3 to 0. But the way they ask the question...Maybe it undergoes A redox reaction, so maybe "either reduction or oxidation" (like saying A substitution reaction, so can be electrophilic OR nucleophilic).

 

[mujtabashahnawaz]

N is reduced from +3 to 0

 

[nikhil000]

which isomer of C4H10 forms three alkenes on dehydration ?
A.butan-1-ol B. butan-2-ol C. 2-methylpropan-1-ol D. 2-methylprapan-2-ol

 

[mujtabashahnawaz]

which isomer of C4H10 forms three alkenes on dehydration ?
A.butan-1-ol B. butan-2-ol C. 2-methylpropan-1-ol D. 2-methylprapan-2-ol

Butane-2-ol because in A and C, three alkenes doesn't form and in D, dehydration doesn't take place

 

[nikhil000]

Butane-2-ol because in A and C, three alkenes doesn't form and in D, dehydration doesn't take place

Thanks a bunch...But, can you please explain me my drawing the structures ......

 

[smartangel]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
please explain 26..

 

[leosco1995]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
please explain 26..

Immediate distillation means that ethanol was converted to ethanal, not ethanoic acid.

46g of ethanol gives you 44g of ethanal.
2.30g of ethanol would therefore give you 2.2g of ethanal.

But the yield was only 70%, so you get 70/100 * 2.2 = 1.54g of ethanal.

 

[smartangel]

Immediate distillation means that ethanol was converted to ethanal, not ethanoic acid.

46g of ethanol gives you 44g of ethanal.
2.30g of ethanol would therefore give you 2.2g of ethanal.

But the yield was only 70%, so you get 70/100 * 2.2 = 1.54g of ethanal.

thanks..could you please explain these as well..i"ll be grateful!
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
in Q6..shouldnt Y be higher as the peak increases when temp is reduced?
and plz explain Q 11, 19,23 as well!

 

[soul1]

Imagine the curve is being depressed by a force from the top left. That makes the X higher (the curve needs to have a high proportion of 'slower' gas molecules), while the Y decreases (along with the Z); (also imagine pulling it up from the X point). Answer is B.

 

[mr.doubtz]

How to solve this one bro?

1. Camphor is a white solid which was used to make the early plastic celluloid. Camphor contains the same percentage by mass of hydrogen and oxygen.What is the molecular formula of camphor? A C10H6O6 B C10H8O C C10H16O D C10H10O2

 

[Saniah]

The correct option to this question is C, I don't really understand this question, a little help will be appreciated!