Chemistry: Post your doubts here!

[nehaoscar]

How is C red and D blue?
Looking at the peaks you get C blue and D red :S
How to do this one???

 

[nehaoscar]

Hello, can you please tell me if it's possible to finish paper 5 in a week? given that at the beginning of said week I never opened any paper and at the end of the same week is the actual exam i.e. 30 October - 5 November?

P5 is not exactly difficult, you just need to know how to plan experiment and the basic techniques. I would advise to revise earlier but in the worst case I believe yes it can be done.

 

[Serial_Ripper]

P5 is not exactly difficult, you just need to know how to plan experiment and the basic techniques. I would advise to revise earlier but in the worst case I believe yes it can be done.

THANK YOU!!

 

[Liv2Stdy]

View attachment 57174
How is C red and D blue?
Looking at the peaks you get C blue and D red :S
How to do this one???

Its not like that. The peak of c is at 450 nm which means that it absorbs all of blue and gives out its complementary color, red and the same thing happens at peak of D, it absorbs all of rwd and gives out the complementary color which is blue.

 

[yash731]

The products obtained by cracking an alkane, X, are methane, ethene and propene. The mole fraction of ethene in the products is 0.5. What is the identity of X?
A C6H14 B C8H18 C C9H20 D C11H24

and

40 An organic compound, X, will react with an excess of calcium metal to produce a salt with the empirical formula CaC4H6O4. What could be the identity of X?
1 ethanoic acid 2 butanedioic acid 3 methylpropanedioic acid

May june 2011 mcq paper-12

 

[The Sarcastic Retard]

The products obtained by cracking an alkane, X, are methane, ethene and propene. The mole fraction of ethene in the products is 0.5. What is the identity of X?
A C6H14 B C8H18 C C9H20 D C11H24

and

40 An organic compound, X, will react with an excess of calcium metal to produce a salt with the empirical formula CaC4H6O4. What could be the identity of X?
1 ethanoic acid 2 butanedioic acid 3 methylpropanedioic acid

May june 2011 mcq paper-12

1)
Mole fraction = [No. of mole of molecule]/[No. of total moles]
Let mole fraction = X
X(C2H4) = 0.5
So we can assume no. of moles of CH4 and C3H6 to be 1 and C2H4 to be 2 so that 2/(1+2+1) = 0.5 mol
So we have products as CH4 + 2C2H4 + C3H6
Total of 8 C and 18 H
Therefore answer is C8H18

2)
1.CH3COOH + Ca --------> Ca(CH3COO)2 = CaC4H6O4 (correct)
2.HOOCCH2CH2COOH + Ca ------------> CaC4H4O4 (Incorrect)
3. I am not sure about this because as per my knowledge the name should be 2-methypropanedioc acid.
HOOCCH(CH3)COOH + Ca ------> CaC4H4O4 (Incorrect)

 

[nehaoscar]

Its not like that. The peak of c is at 450 nm which means that it absorbs all of blue and gives out its complementary color, red and the same thing happens at peak of D, it absorbs all of rwd and gives out the complementary color which is blue.

Ohhh so do you look at the point where it touches the x axis (zero absorbance) for it's colour?

 

[talal096]

Someone told me chemistry AS syllabus changed. Will it effect these Oct/nov 2015 papers as well?
What are the new topics and which topics are removed? Plzz HELP!!!

 

[nehaoscar]

Someone told me chemistry AS syllabus changed. Will it effect these Oct/nov 2015 papers as well?
What are the new topics and which topics are removed? Plzz HELP!!!

No the changes take place from 2016 papers

 

[psychiatrist]

http://onlineexamhelp.com/wp-content/uploads/2014/08/9701_s14_qp_22.pdf
Q2 part iii, iv and v
ASAP

 

[The Sarcastic Retard]

http://onlineexamhelp.com/wp-content/uploads/2014/08/9701_s14_qp_22.pdf
Q2 part iii, iv and v
ASAP

(iii) We are asked to find number of moles of compound in 250cm^3 we found its mole in 25cm^3 in part (ii)
--> (250 * 5 * 10^-3)/25 = 0.05 mol
(iv) Mr = m/n = 6.3/0.05 = 126
(v) Mr of H2C2O4 = 90
So 126 - 90 = xH20
That is 36
Mr of H2O = 18 so x is 2

 

[darks]

Guys i am giving AS this O/N and what i see from past papers is that in recent years the examiner is giving stuff that rarely comes in our exams (e.g position/chain isomers... catalytic convertors and few organic reactions..)
please please please i will be really thankful if anyone could make a small (or maybe big or maybe a single thing) list of things that people usually forget/ miss after doing past papers as it rarely came any year. I am sure that can help everyone giving AS this o/n
thanks in advance

 

[The Sarcastic Retard]

Guys i am giving AS this O/N and what i see from past papers is that in recent years the examiner is giving stuff that rarely comes in our exams (e.g position/chain isomers... catalytic convertors and few organic reactions..)
please please please i will be really thankful if anyone could make a small (or maybe big or maybe a single thing) list of things that people usually forget/ miss after doing past papers as it rarely came any year. I am sure that can help everyone giving AS this o/n
thanks in advance

All you need is a good grasp on the concept. That's it.
Still 2 days are there, practice as many things u can.... But remember u should know ur every concepts.

 

[Metanoia]

Guys i am giving AS this O/N and what i see from past papers is that in recent years the examiner is giving stuff that rarely comes in our exams (e.g position/chain isomers... catalytic convertors and few organic reactions..)
please please please i will be really thankful if anyone could make a small (or maybe big or maybe a single thing) list of things that people usually forget/ miss after doing past papers as it rarely came any year. I am sure that can help everyone giving AS this o/n
thanks in advance

With so little time left, it makes more sense to focus on the main and common concepts rather than a list of "unexpected questions".

Such a "list" will never be accurate nor exhaustive; and would only add unnecessary stress instead.

 

[awesomaholic101]

http://gopapers.net/alevel.html?_9701_w13_ms_22
Question 2.b.ii) Can anyone please explain how the first and second structures is not the same??

 

[The Sarcastic Retard]

http://gopapers.net/alevel.html?_9701_w13_ms_22
Question 2.b.ii) Can anyone please explain how the first and second structures is not the same??

Optical isomer.

 

[sj0007]

can anyone tell me the two geometric isomers of 3-methyl-2-pentenoic acid (CH3CH2C(CH3)=CHCO2H)?
I am confused...............

 

[Metanoia]

can anyone tell me the two geometric isomers of 3-methyl-2-pentenoic acid (CH3CH2C(CH3)=CHCO2H)?
I am confused...............

There is EZ isomerism at the C=C double bonds.

 

[awesomaholic101]

Optical isomer.

How? There's no chiral carbon

 

[The Sarcastic Retard]

awesomaholic101