Chemistry: Post your doubts here!

[imperial]

With cold, dilute KMnO4, the C=C bond turns into C(OH)-C(OH). With hot, concentrated, it turns into C=O and O=C.

But only 2 OH is formed

Edit: There is an OH group down HAHA, I got it now.

 

[imperial]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_11.pdf

27, I know that the fission is homolytic but how to know the expected ratio?

 

[darkxangel]

With cold, dilute KMnO4, the C=C bond turns into C(OH)-C(OH). With hot, concentrated, it turns into C=O and O=C.

Thanks

 

[Raiyan3]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
Q4 please Ahmad Zaeem

You have to use bond engeries.
Since N2 and O2 bonds were broken they are endothermic. And NO bond was formed so exothermic.
=>(N2+O2)-2no=+180
=>(994+496) - 2No= +180
Solve it and you shall find the value of NO

 

[Raiyan3]

"Question number 11 please
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf "

 

[Alice123]

"Question number 11 please
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf "

Its C aluminum carbide
Al4C3+12H2O------->4AL(OH)3+3CH4

CH4+2O2----->2H2O+CO2

Moles of CO2=72/24000=0.003
moles of Al4C3= 0.003/3=0.001 (as ratio of Al4C3:CH4 is 1:3)
now mass of Al4C3= 0.001 into (27+27+27+27+12+12+12)=0.144g
____________________________________________________________________________
dis was done by jiyad ahsan

 

[HubbaBubba]

Can somebody explain those?

q23 - What do they mean by mole fraction is 0.5? How does that affect the identity of X?

q33 - Why is it 1? Why isn't it 2?

q35 -How does nitrogen undergo a redox reaction? It only goes from +3 to 0.

q31 - Where do ionic bonds form? All elements present are non metals?

 

[Alice123]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_11.pdf
Q7

 

[imperial]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf
Q7

Answer is C, the bond angle in 1 is 109 degrees (tetrahedral) carbon is bonded to four atoms
in 2 it's 120 degrees (trigonal planar) because carbon is bonded to three atoms
in 3 it's 104.5 degrees (bent shape) because oxygen contain two free lone pairs of electrons.

 

[white rose]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
can anyone explain me q.4 & 29 thnxx

 

[Raiyan3]

Its C aluminum carbide
Al4C3+12H2O------->4AL(OH)3+3CH4

CH4+2O2----->2H2O+CO2

Moles of CO2=72/24000=0.003
moles of Al4C3= 0.003/3=0.001 (as ratio of Al4C3:CH4 is 1:3)
now mass of Al4C3= 0.001 into (27+27+27+27+12+12+12)=0.144g
____________________________________________________________________________
dis was done by jiyad ahsan

Righttt i understood the process but how do we know its Al4C3? :/

 

[imperial]

Can somebody explain those?

q31 Ammonium ion forms ionic bond, the product is ammonium sulphate which is a salt (ionic compound)

 

[HubbaBubba]

Righttt i understood the process but how do we know its Al4C3? :/

I did it a bit differently and got the correct answer as well.

72/24000 = 0.003 moles of carbon dioxide.
mass of carbon = 0.003 * 12 = 0.0036g.
0.144 - 0.0036 = 0.108 g of X (Aluminium) left.
0.108/27 = 0.004 of Aluminium
Ratio of Al to C
0.004 : 0.003
4 : 3
therefore it is Al4C3

 

[Alice123]

Righttt i understood the process but how do we know its Al4C3? :/

try out every option.. time- consuming

 

[magnesium]

h4rriet http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf 22

 

[Raiyan3]

A

I did it a bit differently and got the correct answer as well.

72/24000 = 0.003 moles of carbon dioxide.
mass of carbon = 0.003 * 12 = 0.0036g.
0.144 - 0.0036 = 0.108 g of X (Aluminium) left.
0.108/27 = 0.004 of Aluminium
Ratio of Al to C
0.004 : 0.003
4 : 3
therefore it is Al4C3

Ahaa that is an awesome method aswell. Thanks a bunch hubbabubba *too cool to tag names*

 

[aleezay]

Somebody please reply fast.. i have 2 hours left. Im done with all the papers back till 2002. Ive gone through my notes once. what should i do right now?? chemguide or the book (coursebook by David Acaster) plz note that I have 2 hours only and went through each looong way back

 

[1597.2217]

Somebody please reply fast.. i have 2 hours left. Im done with all the papers back till 2002. Ive gone through my notes once. what should i do right now?? chemguide or the book (coursebook by David Acaster) plz note that I have 2 hours only and went through each looong way back

I would suggest the guide.

 

[daisyy]

Q 30!
okay here goes, so you know when we find the yield in an ester rxn we use the acid right?
so the mass of the ethanoic acid given is 30, which divided by the mr of the acid
30/60 = 0.5 moles
and in the end the ester formed has mass 22g while its mr is 88, moles of ester formed,
22/88 = 0.25 moles
so if 0.5 moles of acid produces o.25 moles of the ester, we have
(0.25/0.5) x 100 = 50%

hope you got it, dnt mind asking if u didnt.
i'll just do 39 and post it up in a bit

Hey umm im confused in question number 30 why do we use the moles of the ACID not alcohol? :/ and can anyone pleaase explain me questions number 4, 5 and 12 in the same exam? Thank u

 

[imperial]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf

36, need help.