Chemistry: Post your doubts here!

[geek101]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_41.pdf

In 1(b), where did they find atomisation enthalpy of nitrogen from? It's not in the data booklet!
They've given '944' as the value to use while finding enthalpy change for nitrogen. Where did they find that from?? :/

The enthalpy change of atomization of N2 would be, the enthalpy change when 1 mole of gaseous N atoms form from N2.
This reaction would then be: 1/2 N2 (g) > N (g), in order to convert N2 to N atoms only you will need to break the 3 bonds in the structure of N2. Therefore you'll need to see the energy of the three bonds, which is in the data booklet as the bond energy for N---N which is 944. and this will be endothermic because bond breaking is endothermic, so itll be +944.

in the mark scheme there showing this reaction: N2 (g) > 2N3- (g)
but the reaction with all the steps will be : N2 > 2N > 2N3- (all gasses)

hope that helped = )

 

[Xeee]

The enthalpy change of atomization of N2 would be, the enthalpy change when 1 mole of gaseous N atoms form from N2.
This reaction would then be: 1/2 N2 (g) > N (g), in order to convert N2 to N atoms only you will need to break the 3 bonds in the structure of N2. Therefore you'll need to see the energy of the three bonds, which is in the data booklet as the bond energy for N---N which is 944. and this will be endothermic because bond breaking is endothermic, so itll be +944.

in the mark scheme there showing this reaction: N2 (g) > 2N3- (g)
but the reaction with all the steps will be : N2 > 2N > 2N3- (all gasses)

hope that helped = )

OMG ofcourse! Thanks a lot! :')
In the same question, (c) part, I have trouble forming the equation. How do we predict the formation of LiOH? :/ I thought it was Li^2O :/

 

[Usman04]

Ammonium sulfate in nitrogenous fertilisers in the soil can be slowly oxidised by air producing
sulfuric acid, nitric acid and water.
How many moles of oxygen gas are needed to oxidise completely one mole of ammonium
sulfate?
A 1 B 2 C 3 D 4
plz explain this

 

[A star]

Ammonium sulfate in nitrogenous fertilisers in the soil can be slowly oxidised by air producing
sulfuric acid, nitric acid and water.
How many moles of oxygen gas are needed to oxidise completely one mole of ammonium
sulfate?
A 1 B 2 C 3 D 4
plz explain this

easy
(Nh4)2SO4 +4O2 -----> H2SO4 + 2HNO3 + 2H2O
hence D

 

[Hassi123]

http://www.novapapers.com/images/PDF/CIE/A-LEVEL/chemistry/2012jun/9701_s12_qp_43.pdf

Q3 part d. I thought benzene only reacts with br2 if its not aq or with a catalyst. Here there is an excess of br2 (aq) and it reacts with the benzene.
Please help?

 

[knowitall10]

http://www.novapapers.com/images/PDF/CIE/A-LEVEL/chemistry/2012jun/9701_s12_qp_43.pdf

Q3 part d. I thought benzene only reacts with br2 if its not aq or with a catalyst. Here there is an excess of br2 (aq) and it reacts with the benzene.
Please help?

Assalamu Alaykum.
I think you've put the link of the wrong question. Because what you're asking of Q3 is different than what you're actually referring to on the paper.
Please make sure and ask.
If you're sure of it, then please do inform me because most probably i misunderstood the question or something.

 

[Decent gurl]

how do we prepare meta-nitro benzene from benzene?
what's the general scheme of the reaction?

 

[Soldier313]

xhizors JazakAllah khair for those answers! They helped, and yes i'll definitely pray for you inshaAllah.

 

[Hassi123]

Assalamu Alaykum.
I think you've put the link of the wrong question. Because what you're asking of Q3 is different than what you're actually referring to on the paper.
Please make sure and ask.
If you're sure of it, then please do inform me because most probably i misunderstood the question or something.

Oh I'm sorry, it's part e

 

[Hassi123]

C

Assalamu Alaykum.
I think you've put the link of the wrong question. Because what you're asking of Q3 is different than what you're actually referring to on the paper.
Please make sure and ask.
If you're sure of it, then please do inform me because most probably i misunderstood the question or something.

Can you help me with it? It's q3 part e*

 

[Hassi123]

http://www.novapapers.com/images/PDF/CIE/A-LEVEL/chemistry/2012jun/9701_s12_qp_43.pdf

Q3 part E. I thought benzene only reacts with br2 if its not aq or with a catalyst. Here there is an excess of br2 (aq) and it reacts with the benzene.
PLEASE HELP !

 

[knowitall10]

http://www.novapapers.com/images/PDF/CIE/A-LEVEL/chemistry/2012jun/9701_s12_qp_43.pdf

Q3 part E. I thought benzene only reacts with br2 if its not aq or with a catalyst. Here there is an excess of br2 (aq) and it reacts with the benzene.
PLEASE HELP !

Alright alright dude! Chill! My internet wasn't working..
In excess, the bromine will substitute in the 2,4,6 positions..

 

[knowitall10]

how do we prepare meta-nitro benzene from benzene?
what's the general scheme of the reaction?

What's meta-benzene?

 

[Ashique]

knowitall10
could you help with q4 b iii- http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_4.pdf

 

[Asad]

knowitall10
could you help with q4 b iii- http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_4.pdf

Aoa, knowitall10 might have been busy, I guess. So I'll just fix in and solve ur problem, if that's okay.

Q4(ii):
Bonds broken: 4 (C - C) = 4 x 350 = 1400 kjmol-1
Bonds formed: 2 (C=C) = 2 x 610 = 1220 kjmol-1
Enthalpy change = bonds formed - bonds broken, i.e +180 kjmol-1

 

[iKhaled]

knowitall10
could you help with q4 b iii- http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_4.pdf

hey...
C40H82 -------> C16H34 + C24H48

a good way of explaining this question is to see how many bonds u have before the reaction and how many bonds u have after the reaction for example...

before the reaction we have 39 C-C bonds and 82 C-H bonds...after the reaction we have 15+22 = 37 C-C bonds and one C=C bond and 48+34 = 82 C-H bonds

so we have broken 39-37 = 2 C-C bonds and formed 1 C=C bond
bond broken = 2 x 350 = +700
bond formed = -610 = -610
enthalpy = + 90 kjmol^-1 !!

thats it..the mark scheme got the answer as +180 because he has used a different equation in cracking instead of forming C24H48 as our alkene he formed 2 moles of C12H24 and in that way we will have 2 C=C bonds instead of one and 4 C-C bonds instead of 2 because one mole of C12H24 contains 1 C=C bond and 10 C-C bonds so the 2 moles will contain 20 c-c bond and 2 C=C bonds 20+15= 35 so 39-35 = 4 C-C bonds so we had broken 4 C-C bonds and formed 2 C=C bond..in that way u will get 180 kj per mole instead of 90..both are correct though depending on the equation u made

i hope u got it!!

 

[Asad]

i hope u got it!!

heyyyy mann, I solved it first.
Just kidding.

Good job!!

 

[iKhaled]

heyyyy mann, I solved it first.
Just kidding.

Good job!!

 

[freakybandi]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_42.pdf
qs 3 part b

 

[danyaljamil]

can anyone help with this if fe+3 and cl-1 are mixed will overall reaction be feasible and also of cr+2 and I2 here are the E(knot) values: fe+3 to fe+2 0.77 cl2 to cl-1 1.36 cr+3 to cr+2 1.82 I2 to I-1 0.54
mny thanks and sorry dont have marking scheme kinda home made question