Chemistry: Post your doubts here!

[Dukeofwin]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_12.pdf
Question 11 anyone?

 

[daredevil]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Q7

the stronger the reagents, the more the enthalpy change. for P the acid should be weaker than HCl and so it is ethanoic acid. R should be stronger than Q so ammonia is Q and KOH is R. i hope u get it. if u don't then reply and i'll c if i can explain further.

 

[Aymen Ezazi]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf
help needed with these questions.. 17 , 19 , 20 , 28 , 29 , 38 ..

 

[HongYue]

Can you help me with one
question May/June 2008 question 6 ? http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

 

[Aymen Ezazi]

Can you help me with one
question May/June 2008 question 6 ? http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

Mass of ice= d*v, 1.00*1*10^-3 = 1*10^-3 g
Number of moles of ice = m /Mr , 1*10^-3/18 = 5.6*10^-3 mol
use pv=nRT , V=nRT/p = 5.6*10^-3 * 8.31 * 596/ 101*10^-3 = 2.7*10^-6 * 10^6 =2.7dm^3

 

[biba]

thanks a lot

welcum

 

[biba]

Oh and ive got another question:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_1.pdf Q:40th

only 1 and 2 are correct ... in 1 u need to use ur info related to esters... the NaOH wil break the compound from wher -CO2 is present henca an alcohol and corboxylic salt wld be formed... in 1 they have shown the alcohol and in 2 they have shown u the salt! 3 is incorrect because if u look at the stucture in 3 they have totally eliminate the double bond, that is incorrect

 

[Rahma Abdelrahman]

here is another one can you help me with it please

LOL! I actually have the same doubts.. I posted them yesterday but no one answered yet!

daredevil Can u help here?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_11.pdf
please help
question 21, 23, 28, 29, 31

Nov 09 P12, can someone explain Q 18 , Q20 , Q22_Why not B? And Q40 ...
And in June 2010 P11 Q35?!!! How is it C?!! How is Carbon wrong while Sulfur is right?!!! I really don't get it!
Please reply asap ...

Thanks in advance

 

[ahmed abdulla]

only 1 and 2 are correct ... in 1 u need to use ur info related to esters... the NaOH wil break the compound from wher -CO2 is present henca an alcohol and corboxylic salt wld be formed... in 1 they have shown the alcohol and in 2 they have shown u the salt! 3 is incorrect because if u look at the stucture in 3 they have totally eliminate the double bond, that is incorrect

can u help plz

 

[HongYue]

Mass of ice= d*v, 1.00*1*10^-3 = 1*10^-3 g
Number of moles of ice = m /Mr , 1*10^-3/18 = 5.6*10^-3 mol
use pv=nRT , V=nRT/p = 5.6*10^-3 * 8.31 * 596/ 101*10^-3 = 2.7*10^-6 * 10^6 =2.7dm^3

THX !!

 

[strangerss]

Mass of ice= d*v, 1.00*1*10^-3 = 1*10^-3 g
Number of moles of ice = m /Mr , 1*10^-3/18 = 5.6*10^-3 mol
use pv=nRT , V=nRT/p = 5.6*10^-3 * 8.31 * 596/ 101*10^-3 = 2.7*10^-6 * 10^6 =2.7dm^3

in finding the mass why did you multiply by 1*10^-3 ?

 

[strangerss]

Noo Q19 (B) and Q28 (A) according to the mark scheme

answer is B
amount of sulphite use = conc x vol
= 0.1 x (25/1000)
=2.5x10^-3mol
2 electrons are lost
amount of electrons lost = 2 x 2.5 x 10^-3 ==== 5 x 10^-3 mol
amount of electorns gained by metallic salt = amount of electrons lost by sulphite
= 5 x 10^-3 mol
amount of metallic salt used = 0.1 x (50/1000) ==== 5 x10^-3
amount of electrons gained PER MOLE of salt = (5 x 10^-3)/(5x10^-3) = 1 unit
hence oxidation state of metallic salt decreases by 1 unit meaning the oxidation satate becomes +2 from +3!!! this is for the question 9 , some other person posted it

 

[Rahma Abdelrahman]

here is another one can you help me with it please

LOL! I actually have the same doubts.. I posted them yesterday but no one answered yet!

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_11.pdf
please help
question 21, 23, 28, 29, 31

Nov 09 P12, can someone explain Q 18 , Q20 , Q22_Why not B? And Q40 ...
And in June 2010 P11 Q35?!!! How is it C?!! How is Carbon wrong while Sulfur is right?!!! I really don't get it!
Please reply asap ...

Thanks in advance
strangerss Can u try to help here?

 

[strangerss]

LOL! I actually have the same doubts.. I posted them yesterday but no one answered yet!





Thanks in advance
strangerss Can u try to help here?

SOSO247 OKay , in question 21 the only way to solve it is by drawing the displayed formula of the the compound. the first thing I did is I drew the cyclohexene ring you know how right? in the cyclo hexene there is 12 hydrogen atoms and 6 carbon atoms , then from the sixth carbon atom I drew a bond and counted till I reached the 11th carbon atom where I put a double bond because in the question the cis isomer is between the 11th and 12th carbon atom right? the I drew the remaing carbon atoms after the 11th one which are 9 at the last carbon atom I put the aldehyde group because it's pretty obvious it's always at the last. now the last and probably most important step is the number of double bonds between the carbon atoms , now we know that there are 12 hydrogen in the cyclohexene and two for the cis isomer and the total number of hydrogen atoms is 28(from the question) so 28-14=14 carbons atoms are left to be bonded to the carbon chain , so if you give each carbon atom a hydrogen till you used 14 , you add a double bond between the carbon atoms with only three bonds and you will get six double bonds ..I will put the pic. I drew if you didn't get it ok?...question 23 it's C because we get a polychroalkene when we polymerise the monomer given right? then by reacting with water a nucleaphilic substitution reaction takes place in which the hydroxide ions which acts as a nucleaphile displaces the weaker nucleaphile the chlorine atom , it's exactly like when reacting a halognoalkane with sodium hydroxide and we get an alcohol , in A we cannot hydrate an alkane because there are no double bonds , and in B and D it's the same case we cannot oxidise an alkane , so C is correct. question 28 I really got no clue :/ . question 29 it's B because we know that a halogenoalkane plus CN will give a nitrile and when we hydrolyse a nitrile we get a carboxylic acid , when CN displaces Br in B , the final product formed will have a carbon atom attached to an ethyl group which is shown in the diagram given , notice how all the other products formed will not have an ethy group that is the C2CH3 being attached to the carbon atom that was attached to the br , did you get it ?and question 31 I don't know :/ ..hope I helped

 

[strangerss]

LOL! I actually have the same doubts.. I posted them yesterday but no one answered yet!





Thanks in advance
strangerss Can u try to help here?

RAHMA ABDELRAHMAN , I will see through your questions

 

[ahmed abdulla]

answer is B
amount of sulphite use = conc x vol
= 0.1 x (25/1000)
=2.5x10^-3mol
2 electrons are lost
amount of electrons lost = 2 x 2.5 x 10^-3 ==== 5 x 10^-3 mol
amount of electorns gained by metallic salt = amount of electrons lost by sulphite
= 5 x 10^-3 mol
amount of metallic salt used = 0.1 x (50/1000) ==== 5 x10^-3
amount of electrons gained PER MOLE of salt = (5 x 10^-3)/(5x10^-3) = 1 unit
hence oxidation state of metallic salt decreases by 1 unit meaning the oxidation satate becomes +2 from +3!!! this is for the question 9 , some other person posted it

can u answer plz ...
i posted it several times but no one answered

 

[Rahma Abdelrahman]

SOSO247 OKay , in question 21 the only way to solve it is by drawing the displayed formula of the the compound. the first thing I did is I drew the cyclohexene ring you know how right? in the cyclo hexene there is 12 hydrogen atoms and 6 carbon atoms , then from the sixth carbon atom I drew a bond and counted till I reached the 11th carbon atom where I put a double bond because in the question the cis isomer is between the 11th and 12th carbon atom right? the I drew the remaing carbon atoms after the 11th one which are 9 at the last carbon atom I put the aldehyde group because it's pretty obvious it's always at the last. now the last and probably most important step is the number of double bonds between the carbon atoms , now we know that there are 12 hydrogen in the cyclohexene and two for the cis isomer and the total number of hydrogen atoms is 28(from the question) so 28-14=14 carbons (u mean Hydrogen )atoms are left to be bonded to the carbon chain , so if you give each carbon atom a hydrogen till you used 14 , you add a double bond between the carbon atoms with only three bonds and you will get six double bonds ..I will put the pic. I drew if you didn't get it ok?...question 23 it's C because we get a polychroalkene when we polymerise the monomer given right? then by reacting with water a nucleaphilic substitution reaction takes place in which the hydroxide ions which acts as a nucleaphile displaces the weaker nucleaphile the chlorine atom , it's exactly like when reacting a halognoalkane with sodium hydroxide and we get an alcohol , in A we cannot hydrate an alkane because there are no double bonds , and in B and D it's the same case we cannot oxidise an alkane , so C is correct. question 28 I really got no clue :/ . question 29 it's B because we know that a halogenoalkane plus CN will give a nitrile and when we hydrolyse a nitrile we get a carboxylic acid , when CN displaces Br in B , the final product formed will have a carbon atom attached to an ethyl group which is shown in the diagram given , notice how all the other products formed will not have an ethy group that is the C2CH3 being attached to the carbon atom that was attached to the br , did you get it ?and question 31 I don't know :/ ..hope I helped

Thanks
Btw my questions r the same but with different no. due to different variant!
And.. check the part I marked with red above

 

[Monysa Adhikary]

hey I want p1, p2 and p4 questions of organic chemistry only....... exam is near n its total mess.
Can anyone help me?????

Also,I have got problems in the isomerism: how im not gonna solve it?
.................... waiting for the tips

 

[strangerss]

can u answer plz ...
i posted it several times but no one answered

okay give me a sec.

 

[strangerss]

Thanks
Btw my questions r the same but with different no. due to different variant!
And.. check the part I marked with red above

yeah you're right .. so you got it ? great to hear that that question 29 was exhausting