GT for Chemistry paper 22 AS.

[littlecloud11]

Well, I don't remember any trio being formed! Are you sure it was a triol? Which question are you talking about? It would help if you posted the whole question as it was.

the very last part of question 4. when the aldehyde is reduced by NaBrH4 to forma secondary alcohol. initially 2 alcohol groups were already present so the final product was a triol.

 

[littlecloud11]

anyone knows for SURE how many marks were there for the skeletal formula?

 

[00tanveer]

The instructions given on the front page of the question paper said to WRITE IN BLUE OR BLACK INK. YOU CAN USE PENCIL FOR DIAGRAMS, GRAPHS and another thing I don't remember. You judge.

 

[00tanveer]

Oh yeah yeah, now I remember! Thanks Littlecloud!

 

[00tanveer]

Effect of high pressure: The spacing of the molecules decreases. Therefore, frequency of collisions increases which leads to an increase in the rate of formation of methanol.
Effect of high temperature: This is increases the average kinetic energy of the molecules. So, proportion of molecules exceeding activation energy increases. This leads to an increase in the rate of formation of methanol.
Effect of a catalyst: This reduces the activation energy of the reaction. So, frequency of effective collisions increases leading to an increase in the rate of formation of methanol. That's about it.

 

[aom]

Guys for the reaction part in Q 3 i wrote Elimination, oxidation and addition.....Are they correct?

same same

 

[00tanveer]

Hmm yeah, you got that right.

 

[workaholic]

Okay guys to settle one thing the question on the formation of methanol Whether it was reversible or not we had to just tell in general how the temp. pressure and catayslt affect it. But ive got a doubt they wrote the temp. as 600K so i converted it too 327C and well thats a low temp. So i wrote the temp given to the reaction is low (not as high as other commercial processes) this will decrease the rate of formation because the average kinetic energy of the molecules decrease. Do u think he'll except this ?

327 is a high temperature for this reaction as it was exothermic so while the reaction takes place it will also generate heat thus its a pretty good temp..........

 

[littlecloud11]

Oh yeah yeah, now I remember! Thanks Littlecloud!

no problem.

 

[00tanveer]

AlCl3 is fine. Just chill.

 

[angelicsuccubus]

the very last part of question 4. when the aldehyde is reduced by NaBrH4 to forma secondary alcohol. initially 2 alcohol groups were already present so the final product was a triol.

yeh you're right, it's OHCH2CH(OH)CH2OH

 

[Pals_1010]

same same

1) Elimination/Dehydration

2) Oxidation

3) Electrophilic Addition

 

[littlecloud11]

Oh yeah yeah, now I remember! Thanks Littlecloud!

do you happen to remember the marks for the skeletal formula?

 

[aom]

1) Elimination/Dehydration

2) Oxidation

3) Electrophilic Addition

what is the electophile??!! its only hydration or addition.

 

[Mustehssun Iqbal]

One more thing about enthalpy change. How was it 129, + or -. mine was coming 400 something
I asked some candidate( s ) who got 129 kJper mol , but they took also the enthalpy change of combustion of H2( g ) while making the cycle ( Hess's law ). I thought data of enthalpy change of combustion of H2( g ) was a trick! Because there's no enthalpy change from H2 ( g ) to H2 ( g )!
Anyone else got this??

 

[JD REBORN]

The skeletal formula and optical isomers marks were 3 each.I think for skeletal 1 was for drawing two structures 1 was for showing cis trans isomerism and 1 was for drawing proper skeletal formula.As for the element which burns in chlorine with a coloured flame it could have been sodium,sulphur,phophorus.But what about magnesium doesnt it burn with a white flame?

 

[good man12]

yeah it was a triol........and yeh electrophilic addition or hydration...the skeetal formula i am confirmed was 2 marks actually..

 

[JD REBORN]

One more thing about enthalpy change. How was it 129, + or -. mine was coming 400 something
I asked some candidate( s ) who got 129 kJper mol , but they took also the enthalpy change of combustion of H2( g ) while making the cycle ( Hess's law ). I thought data of enthalpy change of combustion of H2( g ) was a trick! Because there's no enthalpy change from H2 ( g ) to H2 ( g )!
Anyone else got this??

It was -129 100%

 

[Pals_1010]

what is the electophile??!! its only hydration or addition.

Alkenes undergo electrophilic addition

 

[good man12]

One more thing about enthalpy change. How was it 129, + or -. mine was coming 400 something
I asked some candidate( s ) who got 129 kJper mol , but they took also the enthalpy change of combustion of H2( g ) while making the cycle ( Hess's law ). I thought data of enthalpy change of combustion of H2( g ) was a trick! Because there's no enthalpy change from H2 ( g ) to H2 ( g )!
Anyone else got this??

there is an enthalpy change when H2 goes to H2O and thats what we apply in hesses aw when using values of combustion...it was -129