Chemistry: Post your doubts here!

[Batguy]

Aslm...
What does this part of the chemistry syllabus means? "(h) show understanding of, and use, the Brønsted-Lowry theory of acids and bases, including the use of the acid-I, base-II concept"
What's the acid-1, base 11 concept means?

Acid proton donner base proton acceptor hpe so

 

[Haya Ahmed]

People .. is this answer , the same as mine ?
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_22.pdf
Q5 c(ii)

marking scheme : >CO or carbonyl absent
my answer : It is not ketone .. (ketone absent)

At last .. Is carbonyl the same as ketone ?

 

[thats_me]

Carbonyl means ketone & aldehyde both are absent

People .. is this answer , the same as mine ?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_22.pdf
Q5 c(ii)

marking scheme : >CO or carbonyl absent
my answer : It is not ketone .. (ketone absent)

At last .. Is carbonyl the same as ketone ?

 

[AbbbbY]

People .. is this answer , the same as mine ?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_22.pdf
Q5 c(ii)

marking scheme : >CO or carbonyl absent
my answer : It is not ketone .. (ketone absent)

At last .. Is carbonyl the same as ketone ?

I'd write Carbonyl not present OR Aldehyde/Ketone not present.

Just writing ketone not present doesn't say whether if aldehyde is present or not and since it's DNPH if it's negative, there's no way either is present so go with carbonyl.

 

[syed1995]

People .. is this answer , the same as mine ?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_22.pdf
Q5 c(ii)

marking scheme : >CO or carbonyl absent
my answer : It is not ketone .. (ketone absent)

At last .. Is carbonyl the same as ketone ?

No.

part ii is reaction with 2,4 DNPH.. which tells us if there is a carbonyl group present or not.

Carbonyl = Ketone AND Aldehyde both not just ketone..

I mean since you have already told in part i, that it's not a aldehyde the examiner might give you marks for it's not a ketone. But I wouldn't risk it.

The correct Answer for this will be. "The compound doesn't have a carbonyl group" or "No Ketone or Aldehyde present in compound R".

 

[Haya Ahmed]

syed1995
AbbbbY
thats_me

Thanks Guys !! anyway my answer was "It is neither ketone nor aldehyde" I think I'm on the safe side .. as carbonyl didn't come to my mind at that time =))

 

[hope4thebest]

What is meant by heating to a constant mass? This term is often used in Paper 5. The question was that how you would ensure that decomposition is complete and the answer suggested heating to a constant mass. Any idea people? Thank You

 

[Suchal Riaz]

no. H2 and Ni only reduces Alkenes to alkanes

btw check this image. I found it in a doc. It summarizes which and what get oxidize and reduce.
View attachment 41128
View attachment 41129

no.. i said that H2 n Ni reduces both alkenes n carbonyl compounds... n u said that they only reduce alkenes...

i didn't know that H2 and Ni reduce CHO but the markscheme of s13/21 says so.
but how is it possible that POTASSIUM PERMANGANATE CAN NOT OXIDISE CHO into CO2H? that is not possible. this oxidising agent is an EXTREMELY powerful reagent. and it will oxidise almost everything. if very concentrated and heated it can oxidise all Carbons and hydrogen in any organic compound into CO2 and H2O. i believe this is another time CIE is wrong. first time being that elimination occurs in alcohol.

 

[mehria]

i didn't know that H2 and Ni reduce CHO but the markscheme of s13/21 says so.
but how is it possible that POTASSIUM PERMANGANATE CAN NOT OXIDISE CHO into CO2H? that is not possible. this oxidising agent is an EXTREMELY powerful reagent. and it will oxidise almost everything. if very concentrated and heated it can oxidise all Carbons and hydrogen in any organic compound into CO2 and H2O. i believe this is another time CIE is wrong. first time being that elimination occurs in alcohol.

KMnO4 can oxidise CHO in the presence of H2SO4....

 

[Suchal Riaz]

KMnO4 can oxidise CHO in the presence of H2SO4....

KNoO4 can oxidise everything that any oxidising agent can. and obviously in presence of H+ ion.
CIE gone mad

 

[mehria]

KNoO4 can oxidise everything that any oxidising agent can. and obviously in presence of H+ ion.
CIE gone mad

lol n KMnO4 cn only oxidise aldehydes
it must b just to keep everythng simple for our age group... they knw everythng mch better thn us...

 

[Haya Ahmed]

Is it okay to draw the displayed formulae instead of the structure formulae in the exam ? or we should stick to structural formula as asked ? and will they reduce marks or what ?!

 

[Haya Ahmed]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_21.pdf

Q3 c (i) why there is 2 lone pairs around the Cl .. isn't it supposed to be 1 lone pair only to complete the 8 electrons in the valence shell ?!

 

[Suchal Riaz]

lol n KMnO4 cn only oxidise aldehydes
it must b just to keep everythng simple for our age group... they knw everythng mch better thn us...

i am talking after reading research papers from top universities including university of new york.
and that can NOT be wrong. I have even seen come textbook used in BS in chemistry in cambridge university containing things that are against our A level syllabus.
they know everything but they have simplified the things to the point of being wrong. and i can handle a syllabus 10X the current size. and i hate to learn wrong things.

 

[mehria]

i am talking after reading research papers from top universities including university of new york.
and that can NOT be wrong. I have even seen come textbook used in BS in chemistry in cambridge university containing things that are against our A level syllabus.
they know everything but they have simplified the things to the point of being wrong. and i can handle a syllabus 10X the current size. and i hate to learn wrong things.

but we get marks frm these wrng things... in such cases we have to go with the flow...

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_21.pdf

Q3 c (i) why there is 2 lone pairs around the Cl .. isn't it supposed to be 1 lone pair only to complete the 8 electrons in the valence shell ?!

three electrons are bonded to F. so out of 7 electron 3 are bonded, 4 are lonely guys. so 2 lone pairs.

 

[Batguy]

wats expansion of octate rule ._. :'(

 

[Suchal Riaz]

but we get marks frm these wrng things... in such cases we have to go with the flow...

thats what i am forced to do.
if i get to study a university of cambridge i will go to the head of chemistry of CIE with a few grads of chemistry and break his head.

 

[Haya Ahmed]

three electrons are bonded to F. so out of 7 electron 3 are bonded, 4 are lonely guys. so 2 lone pairs.

Ohh thanks how stupid was that ! :/ .. .anyways Is it okay to draw the displayed formulae instead of the structure formulae in the exam ? or we should stick to structural formula as asked ? and will they reduce marks or what ?!

 

[mehria]

thats what i am forced to do.
if i get to study a university of cambridge i will go to the head of chemistry of CIE with a few grads of chemistry and break his head.

it's ok...calm down brother