Chemistry: Post your doubts here!

[Jaf]

which isomer forms 3 alkenes on dehydration?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol
its B bt i cnt get more than 2 alkenes.could u plz explain?

For butan-2-ol, the possible alkenes are
but-1-ene
cis but-2-ene
trans but-2-ene

 

[MysteRyGiRl]

You're missing important details of the question here. Please give the link of the original question.

there isnt anything missing :s
its M/J 10 ques no.5

 

[Jaf]

0.2 mol of a hydrocarbon undergo complete combustion 2 give 35.2 g of carbondioxide 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
its C but how

Moles of CO2 ---> 35.2/44 = 0.8
Moles of H2O ---> 14.4/18 = 0.8
So if 0.2 moles of the hydrocarbon will give 0.8 of each of CO2 and H2O, 1 mole of the hydrocarbon will give 4 moles of each of CO2 and H2O. We can not form the equation.
CxHy + 6O2 -------> 4CO2 + 4H2O
x = 4, y = 8
So the hydrocarbon is C4H8. Are you sure your answer is correct? Can you please check?

 

[MysteRyGiRl]

For butan-2-ol, the possible alkenes are
but-1-ene
cis but-2-ene
trans but-2-ene

oki thnx

 

[MysteRyGiRl]

Moles of CO2 ---> 35.2/44 = 0.8
Moles of H2O ---> 14.4/18 = 0.8
So if 0.2 moles of the hydrocarbon will give 0.8 of each of CO2 and H2O, 1 mole of the hydrocarbon will give 4 moles of each of CO2 and H2O. We can not form the equation.
CxHy + 6O2 -------> 4CO2 + 4H2O
x = 4, y = 8
So the hydrocarbon is C4H8. Are you sure your answer is correct? Can you please check?

my bad its D thnx

 

[MysteRyGiRl]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
ques no 1,3, 28 and 38 plzz

 

[Jaf]

there isnt anything missing :s
its M/J 10 ques no.5

Yeah there is. You didn't give the states of the compounds in the first equation.
So this is the Hess Cycle:
[EDIT: The post messed up the Hess Cycle :/ )

So +38 - 214 = -176 kJ.
But we're asked the enthalpy change of formation of iodotetrachloride. In the reaction pathway we chose, 2 moles are forming. So we'll divide the answer my 2. -176/2 = -88kJ/mol.

 

[MysteRyGiRl]

^sory

 

[MysteRyGiRl]

thnx

 

[MysteRyGiRl]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
ques no 1,3, 28 and 38 plzz

and ques no 20 aswell

 

[Jaf]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
ques no 1,3, 28 and 38 plzz

3 - the largest angle would be y because y is the angle between atoms which have no lone pairs and are thus tetrahedrally arranged (109.5 angle). So answer is B.

28 - look closely at all the options. in the first one, Br would be substituted by CN followed by it's hydrolysis to acid. in the question the carbon which forms an acid (which was originally of the CN part) is attached to another carbon which is only attached to a hydrogen and ethyl group and alkyl. the first option would have this carbon attached to a methyl group.

try using this logic with all the options. B will be the answer.

38 - oxidation of ethanol either requires heat under reflux or gentle heating in simple distillation. in the appartus given, neither is happening. since 1 is not true the only option left is C.

 

[Jaf]

and ques no 20 aswell

This will takes quite some playing around and calculating to do this question. I doubt I'll be able to explain this here or that you'll be able to understand it by mere words. It's best if you skip this question (because you could use your time on more important questions). Don't worry there's no concept in it which you may not already know. You just need to count the number of hydrogens.

 

[Xialay Khan]

where can i get the specimen papers from ? papers leading from 2000 till 2010 ? 5070 olevels...pls guide me a little

 

[MysteRyGiRl]

3 - the largest angle would be y because y is the angle between atoms which have no lone pairs and are thus tetrahedrally arranged (109.5 angle). So answer is B.

28 - look closely at all the options. in the first one, Br would be substituted by CN followed by it's hydrolysis to acid. in the question the carbon which forms an acid (which was originally of the CN part) is attached to another carbon which is only attached to a hydrogen and ethyl group and alkyl. the first option would have this carbon attached to a methyl group.

try using this logic with all the options. B will be the answer.

38 - oxidation of ethanol either requires heat under reflux or gentle heating in simple distillation. in the appartus given, neither is happening. since 1 is not true the only option left is C.

thanx a million evnthough i ddnt get the second question btw ur right but the answer is C in the frst question

 

[MysteRyGiRl]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf
ques no 1, 2,28,40 plzzz

 

[Jaf]

thanx a million evnthough i ddnt get the second question btw ur right but the answer is C in the frst question

Oops LOL sorry.

 

[Jaf]

thanx a million evnthough i ddnt get the second question btw ur right but the answer is C in the frst question

try drawing all the structures in the question. you'll know exactly what I'm talking about.

 

[MysteRyGiRl]

try drawing all the structures in the question. you'll know exactly what I'm talking about.

okazzz

 

[Xialay Khan]

where can i get the sample papers from ? chemistry 5070

 

[MysteRyGiRl]

try drawing all the structures in the question. you'll know exactly what I'm talking about.

i got it n ur awsum