Chemistry: Post your doubts here!

[PANDA-]

why is there no hydrogen bonding btw two CH3F molecules and aldehydes n plz any1 give a brief explanation y these 2 have permanent dipole interactions n not hydrogen bonding n in which cases wud hydrogen bonding occur??

There's no hydrogen bond between CH3F molecules because there is no H-F bond, F is bonded to C here, not H. Also, in aldehydes, there's no H-O bond, the O is bonded to C. I suggest you revise hydrogen bonding from the textbook.

Hydrogen bonding occurs between H that is bonded to F, O or N in one molecule, and F, O or N bonded to H in another molecule..
Examples:
NH3 can form hydrogen bonds with water.
N-H ---- O-H

HF can form hydrogen bonds with water as well.
H-F ---- O-H

 

[imperial]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s05_qp_2.pdf

4 c (ii)

I don't understand the question, I know what is the compound with a chiral center (R-CHBrCN) but what should I do with it?

 

[Ms.qureshi]

i need chem 2000 & 2001 paper... i'm unable to fimd them :-(

plzzz can Anyone help me????????

 

[PhyZac]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_2.pdf

4 c (ii)

I don't understand the question, I know what is the compound with a chiral center (R-CHBrCN) but what should I do with it?

imperial
See they said to draw the displayed formula from the isomers of one compound.

Therefore. You draw both optical versions.

 

[mominzahid]

Hey.. I have some problems in this paper.. In q2(iii) please explain how the rate of the reaction is calculated from the graph. I get the order of reaction with respect to both reactants. have made the rate equation aswell. cant calculate the rate of the reaction and then the rate constant.
In Q3(iv) please explain to me how the PH is calculated.. If this is related to a concept that is explained somewhere on the internet.
Lastly in the q5(iv) i dont understand how the ratio of both the compounds is being calculated.
Im giving the links to the question paper and marking scheme.
Help would be really appreciated.
Thanks in advance.
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_ms_43.pdf

 

[mominzahid]

There's no hydrogen bond between CH3F molecules because there is no H-F bond, F is bonded to C here, not H. Also, in aldehydes, there's no H-O bond, the O is bonded to C. I suggest you revise hydrogen bonding from the textbook.

Hydrogen bonding occurs between H that is bonded to F, O or N in one molecule, and F, O or N bonded to H in another molecule..
Examples:
NH3 can form hydrogen bonds with water.
N-H ---- O-H

HF can form hydrogen bonds with water as well.
H-F ---- O-H

imperial
See they said to draw the displayed formula from the isomers of one compound.

Therefore. You draw both optical versions.

Hey.. I have some problems in this paper.. In q2(iii) please explain how the rate of the reaction is calculated from the graph. I get the order of reaction with respect to both reactants. have made the rate equation aswell. cant calculate the rate of the reaction and then the rate constant.
In Q3(iv) please explain to me how the PH is calculated.. If this is related to a concept that is explained somewhere on the internet.
Lastly in the q5(iv) i dont understand how the ratio of both the compounds is being calculated.
Im giving the links to the question paper and marking scheme.
Help would be really appreciated.
Thanks in advance.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_43.pdf

 

[PANDA-]

Hey.. I have some problems in this paper.. In q2(iii) please explain how the rate of the reaction is calculated from the graph. I get the order of reaction with respect to both reactants. have made the rate equation aswell. cant calculate the rate of the reaction and then the rate constant.
In Q3(iv) please explain to me how the PH is calculated.. If this is related to a concept that is explained somewhere on the internet.
Lastly in the q5(iv) i dont understand how the ratio of both the compounds is being calculated.
Im giving the links to the question paper and marking scheme.
Help would be really appreciated.
Thanks in advance.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_43.pdf

Sorry. I take AS Chemistry.

 

[imperial]

imperial
See they said to draw the displayed formula from the isomers of one compound.

Therefore. You draw both optical versions.

Thank you, I got it.

---

NaOH in ethanol is used for elimination, NaOH in water is used for substitution, also NaOH + heat is used for hydrolysis (esters).

^ Is this right? did I miss anything? that's what I have learned about NaOH from solving few past papers and it's role in organic chemistry.

Also I have encountered many questions with acids, mainly HCL and H2SO4 in organic chemistry, what is their role? (please include details like heat/hot/cold/conc./dilute and whatever)

 

[falcon678]

Hm, what about the condition?

heat in reflux.....

 

[goodluckayesha]

There's no hydrogen bond between CH3F molecules because there is no H-F bond, F is bonded to C here, not H. Also, in aldehydes, there's no H-O bond, the O is bonded to C. I suggest you revise hydrogen bonding from the textbook.

Hydrogen bonding occurs between H that is bonded to F, O or N in one molecule, and F, O or N bonded to H in another molecule..
Examples:
NH3 can form hydrogen bonds with water.
N-H ---- O-H

HF can form hydrogen bonds with water as well.
H-F ---- O-H

thnq

 

[PhyZac]

Thank you, I got it.

---

NaOH in ethanol is used for elimination, NaOH in water is used for substitution, also NaOH + heat is used for hydrolysis (esters).

^ Is this right? did I miss anything? that's what I have learned about NaOH from solving few past papers and it's role in organic chemistry.

Also I have encountered many questions with acids, mainly HCL and H2SO4 in organic chemistry, what is their role? (please include details like heat/hot/cold/conc./dilute and whatever)

Well, yup that is true. (But depend on your reaction ofcourse)

H2SO4
NaBr + conc. H2SO4 [From ROH to RBr]
dilute H2SO4 heat under reflux [From RCN to RCOOH]
conc. H2SO4, heat. [From ROH to alkene]
conc. H2SO4, heat under reflux. [From ROH + RCOOH to RCOO (ester)]

HCL
I dont know sorry.
Plus I am not 100% sure..but this is what I learned.

 

[imperial]

Well, yup that is true. (But depend on your reaction ofcourse)

H2SO4
NaBr + conc. H2SO4 [From ROH to RBr]
dilute H2SO4 heat under reflux [From RCN to RCOOH]
conc. H2SO4, heat. [From ROH to alkene]
conc. H2SO4, heat under reflux. [From ROH + RCOOH to RCOO (ester)]

HCL
I dont know sorry.
Plus I am not 100% sure..but this is what I learned.

Thank you!

and another question:

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w06_qp_2.pdf

4 c(ii)

I got confused by the term dipoles, both alkene and bromine are non-polar, I first thought it's for confusion but the mark scheme says "dipole on Br2"

Explanation, anyone?

 

[PhyZac]

Thank you!

and another question:

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_2.pdf

4 c(ii)

I got confused by the term dipoles, both alkene and bromine are non-polar, I first thought it's for confusion but the mark scheme says "dipole on Br2"

Explanation, anyone?

See, that sketch shows how.

But reason is, the double bond had high electron density, and therefore, it repel the electron from the top bromine toward the down one, inducing a pole. (it is temporary not permenant)

 

[applepie1996]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_53.pdf
question 2 please the first part

 

[sanii94]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w07_qp_5.pdf

Q1 (e) help please!!

 

[knowitall10]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_53.pdf
question 2 please the first part

What about the first part?

 

[knowitall10]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w07_qp_5.pdf

Q1 (e) help please!!

YOu drew the diagram right? now all of you have to do in (e) is to explain how you'll be using that apparatus to get your enthalpy change of solution. at the end, or probably on the next page, use E= mc4t* to calculate one of the experiments.


*4 stands for "delta"

 

[iKhaled]

What about the first part?

can u fill the table and draw the graph because i am stuck with this question too. i tried to do it yesterday and i spent hours on it but its so difficult to draw the graph

 

[applepie1996]

What about the first part?

you know there is a table given yeah ?
i want to know how exactly can i get the concentration of the acid from the two solutions ?

 

[meobunny]

Aameen Sister.
I saw your work, it's a bit vague...
always mention what volume, what temp, how many concentrations, what apparatus you're using:
So, here, mention that the total volume must be 50 cm3
we have to prepare a minimum of 5 diff conc from 2.00 moldm3 (e.g the ones i mentioned in my last reply)
what mass of Mg ribbon? E.g 5grams, weighed by using a digital scale with the accuracy of 0.01 g
volume of HCl measure using a burette
(mention the method alone will get you a mark, for eg: here, you mention that you are preparing your concentrations by serial dilution and then you state your method)
And always remember that when you're planning an experiment, you are explaining somebody who does not know anything. Examiner ko kuch bhi nahi pata to aap nai usai sara method sehi tareekay say explain kar na ha hai.
U get what i mean?
and you're most welcome.

May Allah Succeed Us All in this world and in the Hereafter

Allak ka maseeha ho yar aap i seriously didnt know anything , thankyou you mademit crystal clear for me Alhumdulillah . ALLAH hum sab ko maamyab karen , Ameen . Well i am so worried for papaer 4 i dont have time to revise AS syllabus at all, and they give a lot of it :O