[AmrinderRai]

My revision pretty much starts today ...
has anyone got any notes on all the reactions I need to know (mainly organic) or can summarise them for me ?? would greatly appreciate it

[d_94]

God. This is sooo freakin' harder than Unit 1!! Ughh.

[Cyber123]

Hey can someone please help me with this question. Sorry I can't post the skeletal shape but it's the January 2012 paper question 14. Thanks
The compound
has the systematic name
A 2-chlorobutane
B 3-chlorobutane
C 1-chloro-1-methylpropane
D 1-chloro-2-methylbutane

[xxsreillyxx]

(Original post by Cyber123)
Hey can someone please help me with this question. Sorry I can't post the skeletal shape but it's the January 2012 paper question 14. Thanks
The compound
has the systematic name
A 2-chlorobutane
B 3-chlorobutane
C 1-chloro-1-methylpropane
D 1-chloro-2-methylbutane

Answer is A.

the cl is on the 2nd carbon.

[xxsreillyxx]

What about question 5 in January 2012 unit 2? About oxidation?
I just cannot grasp Oxidation numbers at all.

Would be much appreciated if someone could explain

[Kasarna]

(Original post by xxsreillyxx)
What about question 5 in January 2012 unit 2? About oxidation?
I just cannot grasp Oxidation numbers at all.

Would be much appreciated if someone could explain

The answer is C. An oxidising agent becomes reducded itself.

If you look at the equation; 2H2S + H2SO4 --> 3H20 + 3S

The oxidation state of sulphur in H2SO4 is -4. Why...Oxygen has oxidation state -2..(-2x3=-6). The hydrogen ions have oxidation state +1 so together +2. This means that sulphur must have oxidation state -4..(-6+2=-4).

Also if you look at the oxidation state of sulphur in hydrogen sulfide (2H2S) it is -4. Why...there are 4 hydrogen ions hence sulphur must have oxidation state -4.

The oxidation state of Sulphur is (-2....in Group 6...2 lone pairs of electrons). The equation also says 3 moles of Sulphur (3x-2=-6).

The oxidation state is sulphur has increased from -4 to -6 meaning it has gained 2 electrons. Therefore it has been reduced.

A bit long-winded but its better to understand how to look at such equations and be able to do them next time.

[xxsreillyxx]

(Original post by Kasarna)
The answer is C. An oxidising agent becomes reducded itself.

If you look at the equation; 2H2S + H2SO4 --> 3H20 + 3S

The oxidation state of sulphur in H2SO4 is -4. Why...Oxygen has oxidation state -2..(-2x3=-6). The hydrogen ions have oxidation state +1 so together +2. This means that sulphur must have oxidation state -4..(-6+2=-4).

Also if you look at the oxidation state of sulphur in hydrogen sulfide (2H2S) it is -4. Why...there are 4 hydrogen ions hence sulphur must have oxidation state -4.

The oxidation state of Sulphur is (-2....in Group 6...2 lone pairs of electrons). The equation also says 3 moles of Sulphur (3x-2=-6).

The oxidation state is sulphur has increased from -4 to -6 meaning it has gained 2 electrons. Therefore it has been reduced.

A bit long-winded but its better to understand how to look at such equations and be able to do them next time.

Thank you

but see when u said

"The oxidation state of sulphur in H2SO4 is -4. Why...Oxygen has oxidation state -2..(-2x3=-6). "
is it not -2x4 since its H2SO4?

Sorry if this is a real stupid mistake....

[Kasarna]

(Original post by xxsreillyxx)
Thank you

but see when u said

"The oxidation state of sulphur in H2SO4 is -4. Why...Oxygen has oxidation state -2..(-2x3=-6). "
is it not -2x4 since its H2SO4?

Sorry if this is a real stupid mistake....

LOL yes this is a stupid mistake I copied out the equation wrong from the paper. The paper has H2SO3 instead of H2SO4...therefore what I had written was correct. It is -2x3=-6

[WindowLickah]

I'm probably going to start Unit 2 tomorrow, my main problem is everything to do with organics, the stupid language you need to use as well :/

However I resat Unit 1 two days ago, and found it went well, other people are saying it was difficult so I pray for low boundaries

If anyone has any revision tips I'd be happy to share

[lydia12]

on the sample paper the question was:

The following liquids have a similar number of electrons per molecule. Suggest which is likely to have the highest boiling point?
A) CH3CH2CH2CH2CH3
B) (CH3)3C0H
C) CH3CH2CH(OH)CH3
D) CH3CH2CH2CH2OH

and the answer was B, but i thought branching decreased boiling point so i thought it was d (as i know OH groups increase boiling point) hellppp

[lydia12]

also why is ethanol made from sugar more carbon neutral than hydrogen made from methane?

[Cyber123]

(Original post by xxsreillyxx)
Answer is A.

the cl is on the 2nd carbon.

Thanks, but what about the methyl group one does that count? Because it has a line going from a carbon and I assumed it'd be a methyl group. Sorry for the silly question.

[quintillion]

This website has useful notes
http://www.knockhardy.org.uk/sci.htm

[fifty_six]

found sumthing hope it helps..

[avipsita]

(Original post by lydia12)
on the sample paper the question was:

The following liquids have a similar number of electrons per molecule. Suggest which is likely to have the highest boiling point?
A) CH3CH2CH2CH2CH3
B) (CH3)3C0H
C) CH3CH2CH(OH)CH3
D) CH3CH2CH2CH2OH

and the answer was B, but i thought branching decreased boiling point so i thought it was d (as i know OH groups increase boiling point) hellppp

I am sorry but what paper is this ?? could u please tell me asap thanks

[quintillion]

(Original post by lydia12)
on the sample paper the question was:

The following liquids have a similar number of electrons per molecule. Suggest which is likely to have the highest boiling point?
A) CH3CH2CH2CH2CH3
B) (CH3)3C0H
C) CH3CH2CH(OH)CH3
D) CH3CH2CH2CH2OH

and the answer was B, but i thought branching decreased boiling point so i thought it was d (as i know OH groups increase boiling point) hellppp

I think the dominant intermolecular forces in D are London forces therefore its boiling point is less than B. Not sure of the answer, just trying

[The-Sinister-666]

(Original post by lydia12)
on the sample paper the question was:

The following liquids have a similar number of electrons per molecule. Suggest which is likely to have the highest boiling point?
A) CH3CH2CH2CH2CH3
B) (CH3)3C0H
C) CH3CH2CH(OH)CH3
D) CH3CH2CH2CH2OH

and the answer was B, but i thought branching decreased boiling point so i thought it was d (as i know OH groups increase boiling point) hellppp

it could have something to do with the hydrogen bonds attracting the oxygen atoms on neighbouring molecules. also option b says (CH3)3C0H, what does the 3 outside bracket mean? 3 lots of CH3 or 3 lots of COH

[lydia12]

(Original post by The-Sinister-666)
it could have something to do with the hydrogen bonds attracting the oxygen atoms on neighbouring molecules. also option b says (CH3)3C0H, what does the 3 outside bracket mean? 3 lots of CH3 or 3 lots of COH

it means lots of CH3

[lydia12]

(Original post by avipsita)
I am sorry but what paper is this ?? could u please tell me asap thanks

its the sample paper

[d_94]

(Original post by fifty_six)
found sumthing hope it helps..

Ahhhmaziingg! Thanks soo muchh <3