ChemP22 a question

[Cindy for sure]

have u all learnt the set up in the second last question?

i mean the appratus used to obtain alkenes from alcohols..

none about it in my book and my teacher haven't ever mentioned anything about it

hopefully only 1 or 2 marks on the question

so BTW what's the substance black? anyone who is sure about it?

 

[xxulfi]

it must be a catalyst becuz thats howm the reaction takes place...........in text books they have given AL2O3 but it cant be that since its a white oxide i think.................so it must be a transition metal catalyst which has an oxide which is black in colour........so i think it was copper...........copper (ii) oxide is black................what do u think?

 

[angel101]

it is DEFINITELY not CuO
the catalyst use dis always sulphuric acid so where did Cu come from??
it was carbon.incomplete combustion gives carbon n heat was given...carbon is black

 

[umer khan]

it is DEFINITELY not CuO
the catalyst use dis always sulphuric acid so where did Cu come from??
it was carbon.incomplete combustion gives carbon n heat was given...carbon is black

t was carbon.incomplete combustion gives carbon n heat was given...carbon is black........ so TRUE

 

[ashhadazam]

Well i am confused on that one... I read it somewheree that it was copper cuz copper(ii)oxide is black.. I am confused as to how carbon could form when we were not combusitng the alcohol :/

 

[kiyane]

hey guys i just wanna ask about chem p22. there was 1 question that say X is broken crockery or pumice. they say to identify a chemical in X. I put Al2O3 was it right??

 

[Xam]

it was copper oxide...

 

[Nevereasy]

Wrong.
X was pumice which is SiO2.
The black thing was whatever compound is formed when SiO2 decomposes (that was because of the heat if you didn't take care to look).
The apparatus can be found on page 340 of the OCR book.

P.S CuO? Sorry to burst your bubble but not possible.

 

[DDGAL]

hey they said that one of the components in X and as far asi know that SiO2 and AL2O3 r used as catalyst so dont u think that writing one of them will score us a mark????

 

[Nevereasy]

It should, since the composition of Pumice is as follows:
%SiO2 : 53.50
%Al2O3 : 10.75
%CaO : 3.78
%MgO : 1.95
%Fe2O3 : 3.22
%K2O : 3.15
%Na2O : 1.60
pH : 6.5

I myself wrote CaO.

Carbon responsible for the black solid? Seems probable... CuO however has got nothing whatsoever to do with dehydration and if your reason for choosing CuO is since it's black, well A LOT of things are black do they get accepted as well? No they don't

 

[azfar kashif]

it is DEFINITELY not CuO
the catalyst use dis always sulphuric acid so where did Cu come from??
it was carbon.incomplete combustion gives carbon n heat was given...carbon is black

t was carbon.incomplete combustion gives carbon n heat was given...carbon is black........ so TRUE

Umer Bhai, combustion kahan ho rhi thi?

 

[madee92]

black solid was carbon sure abt it it is p2 1994

 

[angel101]

FYI azfar it was combustion heat was given n some oxygen was obviously present in the test tube.... :roll:

 

[ashhadazam]

OMG no.. how can combustion take place.. combustion hoti to propene kahan se banti ???

 

[ashhadazam]

ANd the catalyst couldnt be sulfuric acid.. it was a solid :/

 

[ashhadazam]

we only heated it strongly... passed it thru a catalyst which turned black.. no sense of carbon formation i think :s

 

[Sandy]

This might sound weird but I wrote CuO myself. And for the pumice thingy i wrote CaO...are any of these right?

 

[ashhadazam]

I wrote CuO too.. because that was the only thing that fitted :/ !!
Dont knw whether CaO is rite... Many wrote SiO2.. I wrote Al2O3..Its correct.. confirmed with my teacher

 

[Nevereasy]

The reaction itself was dehydration.
No combustion occurred, the black solid formed due to decomposition because of the heat.
It should be noted that Catalysts remain unchanged during a reaction so the alcohol had nothing to do with it.
Does anyone know the products for the decomposition of SiO2?

 

[Nevereasy]

I wrote CuO too.. because that was the only thing that fitted :/ !!
Dont knw whether CaO is rite... Many wrote SiO2.. I wrote Al2O3..Its correct.. confirmed with my teacher

There is NO trace of copper in pumice. How the hell did copper come out of nowhere into the testube care to explain that ?