Chemistry: Post your doubts here!

[Midnight dream]

Paper?

gimme a sec..i ll ask my frnds which paper was it..i didn't do that questio any where.

 

[The Sarcastic Retard]

gimme a sec..i ll ask my frnds which paper was it..i didn't do that questio any where.

Ahan!!

 

[Midnight dream]

Ahan!!

OKAY..THE PAPER IS WAYY PURANA
http://www.acethem.com/pastpapers/a...uestion-paper-2002-winter-paper-2-14953.html/
http://www.acethem.com/pastpapers/a...2-mark-scheme-2002-winter-paper-2-14947.html/
Qustion 5

 

[The Sarcastic Retard]

OKAY..THE PAPER IS WAYY PURANA
http://www.acethem.com/pastpapers/a...uestion-paper-2002-winter-paper-2-14953.html/
http://www.acethem.com/pastpapers/a...2-mark-scheme-2002-winter-paper-2-14947.html/
Qustion 5

Konsa question? xD

 

[Midnight dream]

Konsa question? xD

told u question 5 ka shuru wala question.

 

[The Sarcastic Retard]

told u question 5 ka shuru wala question.

Ahhhh... IDK sorry.

 

[Midnight dream]

Ahhhh... IDK sorry.

no prob

 

[The Sarcastic Retard]

http://www.academia.edu/11211755/9701_w02_qp_1
Q36. How Oxi.no of H doesnt change?

 

[Xaptor16]

Ok so i know the fehling's and tollens tests and what results you get and all
but i need what the actual reaction takes place
like sometimes it asks you to write the product that is formed with the reaction with fehlings and tollens
So can someone give me a example please and state what the product would be?

so you should know that only aldehydes react with Fehling's and Tollen's reagent. what happens it that the aldehyde is oxidized to carboxylic acid in both cases. In case of Tollen's reagent, the Ag+ ions act as a mild oxidizing agent and oxidize the aldehyde, and reduce themselves to Ag atoms, which form the silver mirror. so if they say what will be the product when CH3CH2CHO reacts with tollen's reagent, it'll be CH3CH2COOH. same goes for fehling's reagent. the Cu2+ ions act as a mild oxidizing agent and oxidize the aldehyde to a carboxylic acid, and reduce themselves to Cu+ ions, giving the orange color as a precipitate of copper (I) oxide forms.
please do correct me if I've got anything wrong

 

[Metanoia]

thnkss.. but i was actually asking whether H2 with platinium catalyst reduce the aldehyde or not?
i know NaBH4 will do it..

Yes. H2 will reduce ketone and aldehyde, not sure why the ms says otherwise.

Ok so i know the fehling's and tollens tests and what results you get and all
but i need what the actual reaction takes place
like sometimes it asks you to write the product that is formed with the reaction with fehlings and tollens
So can someone give me a example please and state what the product would be?

You'll get the carboxylate salt RCOO- with Cu2O (red brown ppt) for Fehlings.
And carboxylate salt with Ag ( silver mirror) with Tollens.

 

[Metanoia]

http://www.academia.edu/11211755/9701_w02_qp_1
Q36. How Oxi.no of H doesnt change?

It is +1 before and after reaction.

 

[The Sarcastic Retard]

It is +1 before and after reaction.

I dont get. Sorry. How?
Isnt it +3 and +4?

 

[Lola_sweet]

wht are the products formed when a i) Ketone ii) Carboxylic Acid
reacts with LiAlH4 in dry ether

One is the alcohol ofc as its a reducing agent
but do i need to knw other products?

 

[nehaoscar]

so you should know that only aldehydes react with Fehling's and Tollen's reagent. what happens it that the aldehyde is oxidized to carboxylic acid in both cases. In case of Tollen's reagent, the Ag+ ions act as a mild oxidizing agent and oxidize the aldehyde, and reduce themselves to Ag atoms, which form the silver mirror. so if they say what will be the product when CH3CH2CHO reacts with tollen's reagent, it'll be CH3CH2COOH. same goes for fehling's reagent. the Cu2+ ions act as a mild oxidizing agent and oxidize the aldehyde to a carboxylic acid, and reduce themselves to Cu+ ions, giving the orange color as a precipitate of copper (I) oxide forms.
please do correct me if I've got anything wrong

Yes. H2 will reduce ketone and aldehyde, not sure why the ms says otherwise.



You'll get the carboxylate salt RCOO- with Cu2O (red brown ppt) for Fehlings.
And carboxylate salt with Ag ( silver mirror) with Tollens.

Thanks to both of you!

 

[nehaoscar]

I dont get. Sorry. How?
Isnt it +3 and +4?

NH3
N = -3
So H3 = +3
This means that each H = +1

NH4Cl
N = -3
Cl = -1
Total charge = -4
So H4 = +4
This means that each H = +1

So the oxidation no. of H hasn't changed

 

[Studydayandnight]

After Y, when concentrated. H2SO4, is added why is the OH group removed? Why not the COOH? :s because the formula that I came up with is: CH2=CHCH(OH)CO2H

 

[qwertypoiu]

After Y, when concentrated. H2SO4, is added why is the OH group removed? Why not the COOH? :s because the formula that I came up with is: CH2=CHCH(OH)CO2H

This is dehydration of alcohol. OH group must be removed, along with H from a carbon next-door

 

[Metanoia]

I dont get. Sorry. How?
Isnt it +3 and +4?

We measure oxidation states in terms of each atom.

 

[qwertypoiu]

wht are the products formed when a i) Ketone ii) Carboxylic Acid
reacts with LiAlH4 in dry ether

One is the alcohol ofc as its a reducing agent
but do i need to knw other products?

You don't have to know any other product, except H2O sometimes...

 

[Studydayandnight]

When a mixture of ethanal and propanal is reacted under the same conditions as in step I above, a similar reaction occurs with the formation of compound S, C5H10O2.

CH3CHO + CH3CH2CHO ----> C5H10O
Suggest a structural formula for S.

http://www.franklychemistry.co.uk/GCE_Papers/CIE/2009/June/9701_s09_qp_2.pdf

It's the fifth question in the second variant.

I need the structure because the answer isn't there in the mark scheme for this last part.