Chemistry: Post your doubts here!

[crys123]

tertiary halogenoalkanes are the ones that only proceed through Sn1 mechanism and Dz the only option which consists of a tertiary halogenoalkane
A and B both are primary ones while C is a secondary one
Just in case if you are unsure about what a tertiary one is :In a tertiary halogenoalkane, the carbon atom holding the halogen is attached directly to three alkyl groups which in this case is (Ch3)3CI

ok got it. i thought SN1 mechanism worked for both secondary and tertiary halogenoalkanes. thats why i couldnt understand how both C and D could be right.

 

[Starlight97]

Someone plz give the name for As and A A chemistry book

 

[crys123]

Someone plz give the name for As and A A chemistry book

cambride international AS and A level chemistry coursebook by Roger Norris, Lawrie Ryan and David Acaster. Some people use additional books but this one is pretty much enough for our course.

 

[SIstudy]

Pls help me with these questions
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_11.pdf Q4, Q5,Q6, Q8
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf Q33
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_11.pdf Q7

 

[snowbrood]

how to study chemistry of life chapter no 28 of chemistry a2 i just dont get it

 

[selena]

I was doing mcqs from the redspot chemistry Mcqs book and the questions from the 80s & 90s were extremely difficult and they were from p3 p4 mostly. Are they as level questions or a2??

 

[daredevil]

I was doing mcqs from the redspot chemistry Mcqs book and the questions from the 80s & 90s were extremely difficult and they were from p3 p4 mostly. Are they as level questions or a2??

80's is too far back... have you done all through 2007 - present??
patterns and syllabii have changed continuously over the years. Some of the stuff in the 80's syllabus might not even be in your syllabus. do all variants from 2007 - present THOROUGHLY. then back as far as 2002 and do all papers till then thoroughly until you never forget the questions however they might come in front of you.
i don't think there will be time after all that. but if there still is, do some exercises or practice questions.

 

[Kim Shaw]

hey guys, please help me with this question in equilibria. answer is C. Please explain why..

 

[Kim Shaw]

iron tablets can be bought at chemists to supplement the diet. they contain iron(II)sulfate. which one of the following aqueous reagents could be used under suitable conditions to determine the percentage of iron in the tablets by titration?
A.ethanedioic acid B.Iodine in potassium iodide C.potassium manganate(VII) D.sodium thiosulfate
ans C..plz tell me why C and not the others..thnx

 

[ayanhaider]

Can anyone plz tell me about iodoform test?Im having a problem in it ....

 

[Hassan Ali Abid]

Pls help me with these questions
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_11.pdf Q4, Q5,Q6, Q8
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_1.pdf Q33
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf Q7

9701_s09_qp_1.pdf Q33 ...the ans is D bcz it says that which reactions have enthalpy change of formation so 2. 2C(s) + O2(g) → 2CO(g) cant be the choice as two moles of CO are formed so the choice left 1. so ans is D.

9701_w10_qp_11.pdf Q7....angle b/w H-C-H=109.5 , C-O-O =104.5 , C-C=O = 117 so order is 3-1-2 .

 

[daredevil]

Can anyone plz tell me about iodoform test?Im having a problem in it ....

It is used to test for alcohols (primary and secondary)
NaOH and I2 is added to the sample that is to be tested. yellow precipitate means test is positive for the sample.
I2 is reduced in the process.

 

[SomeStudent]

HELP!
Can someone please explain these two parts? How do we find out what the order is, like whats the procedure?
Part b in the first file.
Part e in the second file.
its Oct/Nov 08

 

[snowbrood]

HELP!
Can someone please explain these two parts? How do we find out what the order is, like whats the procedure?
Part b in the first file.
Part e in the second file.
its Oct/Nov 08

for part e
zero order reaction changing concentration doesnt affect the rate of reaction
first order reaction rate=k*concentration
second order reaction rate=k*(concentration)^2

we kept the concentration of H+ ions constant for line 1 and line 2
so only concentration of H2O2 will affect the rate of reaction
well if u see in line 1 and line 2 there is change in rate of reaction that means that h2o2 has order of 1 or 2
lets see if it is order 1
0.05=k*1 equation 1
k=0.05/1=0.05
now if we put the value of k for line 2 we get
0.05*1.4=0.07
that means h2o2 is order 1
pretty clear right?
now line 3
again increasing the concentration of h2o2 by 0.02 we would expect a increase of 0.4 in relative rate
however we are also changing the concentration of H+. as the change in conc of H+ didn't affect the rate of reaction so it has zero order

 

[SomeStudent]

for part e
zero order reaction changing concentration doesnt affect the rate of reaction
first order reaction rate=k*concentration
second order reaction rate=k*(concentration)^2

we kept the concentration of H+ ions constant for line 1 and line 2
so only concentration of H2O2 will affect the rate of reaction
well if u see in line 1 and line 2 there is change in rate of reaction that means that h2o2 has order of 1 or 2
lets see if it is order 1
0.05=k*1 equation 1
k=0.05/1=0.05
now if we put the value of k for line 2 we get
0.05*1.4=0.07
that means h2o2 is order 1
pretty clear right?
now line 3
again increasing the concentration of h2o2 by 0.02 we would expect a increase of 0.4 in relative rate
however we are also changing the concentration of H+. as the change in conc of H+ didn't affect the rate of reaction so it has zero order

Right. A bit confused in the beginning. We found k by dividing rate by concentration? Shouldn't it be 1/o.o5 instead?

 

[selena]

Can anyone please solve q9 may/June 2004 9701/1. Do is as fast as you can I have a paper tomorrow

 

[selena]

Also q 18 of the same paper(june04p1)

 

[saifeddin]

how to know if a precipitation dissolves in excess or not?
from the practical papers, the cations and anions questions

 

[saifeddin]

Also q 18 of the same paper(june04p1)

okay so 58.5 kg of NaCl is 1000 moles.. meaning that the rest of all the other reagents are going to have 1000 moles each...
you have 1 H atom, which is 1 g/mol. multiply this by a thousand you will get 1 kg of (H). you also have 1 Cl atom in the equation and it's 35.5 g/mol. multiply this by a thousand you will get 35.5 Kg of (Cl). the next is NaOH, with the same way you will find out that it will have 40 Kg per 1000 moles. that's it
i'm as clueless as you are in the other one xD

 

[daredevil]

how to know if a precipitation dissolves in excess or not?
from the practical papers, the cations and anions questions

u need to learn it for all the salts in the syllabus.... in paper 3 data sheet for that is given....
it's basically the tests for anions and cations. if u dont find it or dont get it then tell me and i'll elaborate