Chemistry: Post your doubts here!

[yousef]

for the question u did, i think u can.. if the range is too big then u have to take larger values for a particular no. of blocks. If possible send me the link to the question please. Ill try it and show it to you.

 

[ahmed abdulla]

Can someone help ?

 

[1357911]

I hope its clear.

 

[yousef]

View attachment 36803

I hope its clear.

Thank you .
but the varient which i posted is va' 51 .. and in va'51 if you start from origin ( o , o ) you wont have enough
place to plot ALL the points

 

[1357911]

Thank you .
but the varient which i posted is va' 51 .. and in va'51 if you start from origin ( o , o ) you wont have enough
place to plot ALL the points

Its the same for varient 51. u see only the values and the metal sulphates are different. Actually I did varient 51 in varient 52. there is no differnce. the whole question is the same. and the values plotted are for varient 51. Its the same question u told me.

 

[yousef]

Its the same for varient 51. u see only the values and the metal sulphates are different. Actually I did varient 51 in varient 52. there is no differnce. the whole question is the same. and the values plotted are for varient 51. Its the same question u told me.

But dont you think cie will penalise for making begining part ( unplotted )and using only middle part of graph only ?

 

[Hassan Ali Abid]

Can someone help ?

View attachment 36798

The peak at chemical shift 2.00 ppm is due to R-O-H ....and for the chemical shift 1.26 ...it can be seen that there must be 9 hydrogen atoms in the neighbour of center carbon atom , only then the peak at 1.26 will be produced.
From C4H10O ...if we remove -OH then the remaining thing which we get is C4H9 ...and it can only be produced if three CH3- groups(methyl groups) will be attached to the center carbon atom .....( only in that case we will get 9 H in the same molecular environment) hence the molecular formula of the compound should be (CH3)3-C-O-H.

 

[1357911]

But dont you think cie will penalise for making begining part ( unplotted )and using only middle part of graph only ?

I dont think so. the points are plotted correctly, the gradient is correct. Everything is fine.Plus nothing is mentioned like this in the marking scheme/

 

[Hassan Ali Abid]

In paper 2 May June 2006 in q 5 part d I carried out the reaction in a different series from the mark scheme. I think my technique is also right but the mark scheme only accepts one answer.Here's what I did:
React CH3CH2OH with potassium dichromate to get CH3CHO which is K.
Then react CH3CHO with HCN to get CH3CHOHCN which is L.
Then react CH3CHOHCN with water and dil. HCl to get CH3COOH.
Is this correct? Will it be accepted even though it's not in the mark scheme if it's correct?
Please reply back soon, thank you!

The ans which you have given is wrong ..
the ethanol C2H5OH must be converted to halegonoalkane eg C2H5Br....then this is reacted with ethanolic KCN so the product formed will be C2H5CN ...and further the acid hydrolysis of nitrile will produce carboxylic acid ...ie CH3CH2CooH.
K=C2H5Br NaBr+H2So4=HBr+NaHSO4 . and HBr produced will be reacting to form helogenoalkane.
L=C2H5CN. Ethanolic KCN , heat under reflux
P.s do check the ms ...I hope so im not wrong.

 

[Autumngirl]

The ans which you have given is wrong ..
the ethanol C2H5OH must be converted to halegonoalkane eg C2H5Br....then this is reacted with ethanolic KCN so the product formed will be C2H5CN ...and further the acid hydrolysis of nitrile will produce carboxylic acid ...ie CH3CH2CooH.
K=C2H5Br NaBr+H2So4=HBr+NaHSO4 . and HBr produced will be reacting to form helogenoalkane.
L=C2H5CN. Ethanolic KCN , heat under reflux
P.s do check the ms ...I hope so im not wrong.

I know this is what's written in the ms.
I thought my way would yield the same result but just now I found a mistake in it.
Anyways thank you for your help.
R

 

[Hassan Ali Abid]

I know this is what's written in the ms.
I thought my way would yield the same result but just now I found a mistake in it.
Anyways thank you for your help.
R

Okay .
The mistake which you had made was in the addition of aldehyde and HCN. The product which had written was incorrect.
np.

 

[Hassan Ali Abid]

View attachment 36803

I hope its clear.

The triangle which you have drawn for calculating the gradient is too small and the marks are deducted for that.
P.s its not allowed to take those points which are in table to calculate the 'm' and you have used those points so marks will be penalized.... Am I ryt ??

 

[shanebungaroo]

i need june 1993
paper 3
ms

 

[yousef]

The triangle which you have drawn for calculating the gradient is too small and the marks are deducted foor that.
P.s its not allowed to take those points which are in table to calculate the 'm' and you have used those points so marks will be penalized.... Am I ryt ??

What is the meaning of ( construction lines ) ? is it the triangle ?

 

[periyasamy]

Guys have a question here.
In the picture i post below,I dont get it all three answers given.Can anyone explain it to me.Thanks.

 

[periyasamy]

Another question here guys.Pls help.Thanks a lot.

 

[Hassan Ali Abid]

What is the meaning of ( construction lines ) ? is it the triangle ?

yes im talking about the triangle. bigger triangle must be drawn to calculate the gradient ....

 

[periyasamy]

Guys last question.Pls help.I really dont understand
For aspartic acid ,why isnt there a negative in coo ?Thank u a lot.

 

[halloffame]

Can anyone of you give me the lists of all the electrophiles and nucleophiles .

 

[1357911]

The triangle which you have drawn for calculating the gradient is too small and the marks are deducted for that.
P.s its not allowed to take those points which are in table to calculate the 'm' and you have used those points so marks will be penalized.... Am I ryt ??

nah. Not here. I did the same mistake (making a larger triangle) in my exam, and ended up taking the points which were out of the line. My marks got deducted. As long as those points are EXACTLY on the line. its correct.
Yes. It isnt allowed to take the points from the table. And for ur kind information, I havent used those points from the table.