As chemistry oct 2009 mcq

[kaipai]

Hello all!
First simple query::how do you all preapare for chemistry AS level???What is most imporatant:notes??Book??Tutor???Tell me plz...

now paper question:This quest is 25 of the oct 2009 mcq paper. Plz answer which is crect answer?Explain as well plzz in simple terms. NOw plz tell me how to add pictures/ diagram in this post??e.g i could not add q.23 of the same paper. plz tell me how to add a question from pdf. file without typing.

25 Which equation represents a valid propagation step in the free radical reaction between ethane
and chlorine?
A C2H6 + Cl• ? C2H5Cl + H•
B C2H5Cl + Cl• ? C2H4Cl• + HCl
C C2H6 + H• ? •C2H5  + HCl
D C2H5• + Cl • ? C2H5Cl
good by take care,
regards,
K.pai

[guitarbuddy]

The answer to the question is B..
The explanation is easy. The answer cannot be D since it is a step of termination step.. A is producing an H radical and in C C2H6 is reacting with an H radical.. Propagation step is only possible when the reactant reacts with a halogen, mostly Chlorine and produces a Cl radical or a CxHy radical... Therefore B is the correct answer.

[kaipai]

When no one comes to rescue......
KPai is sad.....
But from the darkness and a question....
comes out the one and only guitar buddy.....
Wonderful my buddy....
You are GREAT!!!!

very many thanksss for your reply....You are corrrect...
I am sorry...but if you can plz... plz...answer the new following questin of may 2010::
Q21. When heated with chlorine, the hydrocarbon 2,2 dimethybutane unddergoes free radical substituion.
IN a propagation step the free radical X• is formed.

            CH3
            |
CH3CH2 C-CH3  + Cl• = X• + HCl
            |
            CH3
How many different forms of X• are possible???
a. 1   B.2 C.3   D.4

Please explain...

Good bye and do take care...

Yours truly,,,,
KaiP

[guitarbuddy]

I dont know the answer exactly but i think it is C (3) because there are 3 carbon atoms in the straight chain and Cl can only attach to  straight chain carbon atoms

[Nid]

When no one comes to rescue......
KPai is sad.....
But from the darkness and a question....
comes out the one and only guitar buddy.....
Wonderful my buddy....
You are GREAT!!!!

very many thanksss for your reply....You are corrrect...
I am sorry...but if you can plz... plz...answer the new following questin of may 2010::
Q21. When heated with chlorine, the hydrocarbon 2,2 dimethybutane unddergoes free radical substituion.
IN a propagation step the free radical X• is formed.

            CH3
            |
CH3CH2 C-CH3  + Cl• = X• + HCl
            |
            CH3
How many different forms of X• are possible???
a. 1   B.2 C.3   D.4

Please explain...

Good bye and do take care...

Yours truly,,,,
KaiP

The halogen radical pulls a hydrogen atom off the alkane to form an alkyl radical.

(CH₃)₃-C-CH₂-CH₃

So one distinct radical can form when a hydrogen atom is taken off the methyl group(or Carbon 1)
CH₂(CH₃)₂-C-CH₂-CH₃*

2nd one can form when a hydrogen atom is taken off the alkyl group(CH₂)
(CH₃)₃-C-CH-CH₃*

And third one can form when a hydrogen atom is taken off the 4th carbon
(CH₃)₃-C-CH₂-CH₂*

Should be C

[kaipai]

Dear Nid!
You are absolutely right....
You are very smart....
Thank you vvvvvvvvv muccccccccchhhhhhh....
But tell me how do you prepare for the chemistry ;:notes,book,,. ofcourse everone studies past paper but tell me what notes to use as my teacher is very bad at preparing notes...could you upload your notes...or tell me where to get from...??plzzzzzzz.

Bye,
Take care.
You are good.
best regards,
Kpai.

[kaipai]

I dont know the answer exactly but i think it is C (3) because there are 3 carbon atoms in the straight chain and Cl can only attach to  straight chain carbon atoms

Dear buddy,
YOU are very v right.
YOu are a great person...
Who taught u so much organic chemy???
Tell me plz what u want to do at bachelor level???Why????Told by mom/pa or personal choice????any ideal???
Good bye, my friend,
Take care.
Goodest regards,
KPai.