Chemistry: Post your doubts here!

[Jiyad Ahsan]

this one ^

ok since nobody praises me i'm going to praise myself
*talking to self* "you're getting an A!, no not 'an' A, 3 A's"

note to self: "stop talking to self..."

 

[daredevil]

Check it out.. daredevil likes my depressing reply to Panda

hahha #respect for accceptance man

 

[Jinkglex]

Actually, KMnO4 is "Silently preferred" in A levels. Basically its stronger and agreed upon to be stronger by most books, so that is what is expected of you

similarly, LiAlBH4 is STRONGER, but NaBH4 is more COMMONLY USED. Select at your own choice.

 

[knowitall10]

KMnO4 is a strong oxidising agent if I'm not mistaken, and K2Cr2O7 is a weak oxidising agent.
You can use K2Cr2O7 for mild oxidation of Alcohol to Aldehydes... Unless a reflux with heat is used, then even K2Cr2O7 can oxidise alcohols directly to carboxylic acids.

Really, i always thought there was no difference... do they mark it wrong or anything if we confuse the two in the exam?

 

[Jiyad Ahsan]

KMnO4 is a strong oxidising agent if I'm not mistaken, and K2Cr2O7 is a weak oxidising agent.
You can use K2Cr2O7 for mild oxidation of Alcohol to Aldehydes... Unless a reflux with heat is used, then even K2Cr2O7 can oxidise alcohols directly to carboxylic acids.

umm yeah that i sorta knew.. i was thinking .. like..Why is one stronger and the other not?..

 

[PANDA-]

Really, i always thought there was no difference... do they mark it wrong or anything if we confuse the two in the exam?

Depends, if they say what reagent is needed to change an alcohol to an aldehyde, KMnO4 is wrong.

 

[Jinkglex]

umm yeah that i sorta knew.. i was thinking .. like..Why is one stronger and the other not?..

Although the mechanism for strength of oxidising agent is not involved in the A2 syllabus at all, its basically left best to say that ones mechanism of action is simply superior in speed or efficiency then the others.

 

[knowitall10]

Depends, if they say what reagent is needed to change an alcohol to an aldehyde, KMnO4 is wrong.

OHH!! I had no idea!

 

[PANDA-]

Actually, KMnO4 is "Silently preferred" in A levels. Basically its stronger and agreed upon to be stronger by most books, so that is what is expected of you

similarly, LiAlBH4 is STRONGER, but NaBH4 is more COMMONLY USED. Select at your own choice.

But KMnO4 would just oxidize the Alcohol into the corresponding carboxylic acid... What if we want the aldehyde then?

 

[Jinkglex]

Depends, if they say what reagent is needed to change an alcohol to an aldehyde, KMnO4 is wrong.

Im quite sure i've done alot of papers that featured KMnO4 in the reaction you specified

 

[daredevil]

Depends, if they say what reagent is needed to change an alcohol to an aldehyde, KMnO4 is wrong.

why would it be wrong :O
can't we ues cold dilute KMNO4 ???

 

[knowitall10]

Although the mechanism for strength of oxidising agent is not involved in the A2 syllabus at all, its basically left best to say that ones mechanism of action is simply superior in speed or efficiency then the others.

What?

 

[Jiyad Ahsan]

Although the mechanism for strength of oxidising agent is not involved in the A2 syllabus at all, its basically left best to say that ones mechanism of action is simply superior in speed or efficiency then the others.

okie dokie

 

[Jinkglex]

But KMnO4 would just oxidize the Alcohol into the corresponding carboxylic acid... What if we want the aldehyde then?

Then you would heat it with a fractional distillation set-up, whereby the volative aldehyde would be evaporated and collected off in a seperate vessel.

 

[Jinkglex]

What?

Basically, its saying that "This is better then that just cause it is". It is actually not a part of our syllabus and if i tried explaining it i would confuse you and me both.

 

[knowitall10]

Basically, its saying that "This is better then that just cause it is". It is actually not a part of our syllabus and if i tried explaining it i would confuse you and me both.

Oh ok...

 

[Jiyad Ahsan]

ok so what you basically say is that since you need to only slightly oxidize an alcohol to an aldehyde you need a weaker oxidizing agent?
because if its stronger like KMnO4 it'll oxidize it directly to carboxylic acid? right? did i get it right?

similarly if i use LiAlH4 it'll convert an acid to alcohol, while nabh4 will turn it into an aldehyde?

 

[PANDA-]

This AS and A Level questions in the same topic seems very unhealthy to both parties.

 

[knowitall10]

Does a liebig condenser or a U tube have any size or capacity? no right?

 

[knowitall10]

ok so what you basically say is that since you need to only slightly oxidize an alcohol to an aldehyde you need a weaker oxidizing agent?
because if its stronger like KMnO4 it'll oxidize it directly to carboxylic acid? right? did i get it right?

similarly if i use LiAlH4 it'll convert an acid to alcohol, while nabh4 will turn it into an aldehyde?

Isn't it all about the oxidising agent (whatever it may be) being in excess?