Chemistry: Post your doubts here!

[Hassan Ali Abid]

Same here! Chemistry AS is a nightmare!. I am trying to gain control over it. I have finished the course too, but Past Papers are worst night mare, i have ever had!

And bro ...prepare the AS chem in parts ..like first u should prepare physical part then inorganic and then organic ...and do highlight the book according to the syllabus ..i mean only imp things ......It will take ..like 4-5 days and once u do it ....u will be so calm at the time revision and dont make the things panic .... InshaAllah it will get easy for you but just give a try .. i hope you understand.

 

[Unknown Killer]

@

Resonable answer
another mark scheme answer which confuse me is :

conditions for changing methylbenzene to chloro methyl benzene as we know is : Uv light and reagent Cl2
but as the markscheme for mj2007 says , it should be Cl2 and hf ! >> whats hf hhh

hf is energy of Photon
Photon is in Light , Ultraviolet Rays ...i.e in Sun Light
So it means , Cl2 with Sun light

 

[yousef]

Chemistry paper 5 ,
Is my scaling right? will i get marks for this..
actually my graph completed more than half of grid but i took a part of pic to zoom the scaling .

 

[1357911]

Chemistry paper 5 ,
Is my scaling right? will i get marks for this..
actually my graph completed more than half of grid but i took a part of pic to zoom the scaling .

The scaling on the y axis is wrong . they should cover more than one half of the graph?? Is it even a half? plus better to start the graph from zero. dont break the graph fom the y axis.

 

[yousef]

The scaling on the y axis is wrong . they should cover more than one half of the graph?? Is it even a half? plus better to start the graph from zero. dont break the graph fom the y axis.

i used more than half of y-axis as well, but to show scaling i took a close pic .
and if we start from 0 , values wouldnt be enough

 

[1357911]

i used more than half of y-axis as well, but to show scaling i took a close pic .
and if we start from 0 , values wouldnt be enough

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.

 

[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 ?