AS Chemistry P2 Prep.

[Jaf]

why does everyone keep calling me 'dude' eventhough my username so clearly states my gender

Because 'dude' is gender neutral.

 

[smartangel]

in preparation of alkenes ..when alcohols or alkyl halides are converted into alkenes..the rxn is an elimination reaction??

 

[donorsolutions]

when 50cm^3 of a hydrocarbon Y is burnt it reacts with exactly 300 cm^3 of oxygen to form 200 cm^3 of C02. water is also formed. deduce the equation for this reaction. answer: C4H8 + 6O2 → 4CO2 + 4H2O..please tell the how to work this one out..its frm chemistry coursebook.

Remember the equation :
CxHy + x+0.25yO2 gives XCO2 + 0.5H2O
you can see that to get the question in this form you have to simplify the moles of the hydrocarbon to 1.
So 50(hydrocarbon), 300 (Oxygen), 200( Carbon Dioxide)..simplifying the hydrocarbon to 1:
1 (hydrocarbon) 6(oxygen), 4 (Carbon Dioxide)
So moles of CO2 as in above equation is the value of X.
So X =4
Moles of O2 are = x+0.25y
4+0.25y=6
gives you y=8
So CxHy becomes C4H8..thats how i do it easy way..just remember to simplify the hydrocarbon volume/moles to 1 and then compare according to the equation.

 

[Henry930821]

Hey... Anyone can tell me when only do we need to use pencil in doing chem paper 2? Drawing graphs etc or?

 

[leosco1995]

in preparation of alkenes ..when alcohols or alkyl halides are converted into alkenes..the rxn is an elimination reaction??

Yep. Elimination or dehydration is the name of the reaction.

 

[fathimaash]

Hey... Anyone can tell me when only do we need to use pencil in doing chem paper 2? Drawing graphs etc or?

ya graphs, diagrams like electolysis of brine or aluminium.. dats it

 

[Henry930821]

ya graphs, diagrams like electolysis of brine or aluminium.. dats it

Owh.. Then drawing diagrams like dot and cross diagram and optical isomers etc use pen right?

 

[fathimaash]

Owh.. Then drawing diagrams like dot and cross diagram and optical isomers etc use pen right?

yes....

 

[smartangel]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w11_qp_21.pdf
Q3d...isnt the formula of calculating enthalpy change..Enthalpy change of products - enthalpy change of reactants...?? ms is doing the opposite..

 

[oldfashionedgirl]

Because 'dude' is gender neutral.

still, its got a very ''guy-thing'' touch to it .....and some other dumb guy literally called me 'bro'.....seriously -.-

 

[smartangel]

guys..can we have some chem discussion now? please answer my question that i"ve posted above!!

 

[mujtabashahnawaz]

Owh.. Then drawing diagrams like dot and cross diagram and optical isomers etc use pen right?

I don't think that we will draw the structures, dot cross diagrams in pencil...i am not sure, so i am gonna make them with pen

 

[saudha]

ok anglegirl...... wht do we do??

 

[mujtabashahnawaz]

in preparation of alkenes ..when alcohols or alkyl halides are converted into alkenes..the rxn is an elimination reaction??

When alcohols are converted into alkenes then reaction is dehydration, but when alkyl halides are converted into alkenes, that is elimination. Don't mix up the names. These are two different reactions. If you will name dehydration one an elimination reaction, then the examiner won't give u marks, so be careful.

 

[leosco1995]

When alcohols are converted into alkenes then reaction is dehydration, but when alkyl halides are converted into alkenes, that is elimination. Don't mix up the names. These are two different reactions. If you will name dehydration one an elimination reaction, then the examiner won't give u marks, so be careful.

Wow... you are right. Good thinking.

 

[mujtabashahnawaz]

Wow... you are right. Good thinking.

Thank you

 

[angelgirl:)]

When alcohols are converted into alkenes then reaction is dehydration, but when alkyl halides are converted into alkenes, that is elimination. Don't mix up the names. These are two different reactions. If you will name dehydration one an elimination reaction, then the examiner won't give u marks, so be careful.

but elemination can refer to both H20 as well as HCl removal

 

[mujtabashahnawaz]

No, the term elimination is only used for alkyl halides, not for H2O removal.

 

[smartangel]

No, the term elimination is only used for alkyl halides, not for H2O removal.

are you sure? isnt elimination the removal of water? :O

 

[mujtabashahnawaz]

Is P4O6 in our syllabus or P4O10? If we are asked for an oxide of Phosphorus, which one will we quote?