Chemistry: Post your doubts here!

[darkxangel]

I think C. (Na can react with both -CO2H and OH, there is 3 in C so -3 but NaOH only with -CO2H so -1) I'm not sure though as I didn't revise from a long time.

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

Number 9, the answer is D but I don't know how to get it.

i didn't quite get it :/
I get the part where Na reacts with both -CO2H and -OH but after that i don't get it ..
and
yes it is C.

 

[h4rriet]

I did draw an ICE, but I don't understand how they got 4(b-x) at the bottom. I just got (b-x)^2

If x moles of HI dissociates, then H2 and I2 gain x/2 moles (mole ratio 2:1). Amount of HI left = b-x. Now, Kp=p(I2)xp(H2)/p(HI)^2. [(x/2)*(x/2)]/(b-x)^2 will simplify to D.

 

[imperial]

i didn't quite get it :/
I get the part where Na reacts with both -CO2H and -OH but after that i don't get it ..
and
yes it is C.

Na reacts with both groups to form ONa- which is charged (-1), there is three so 3 ONa- will form

NaOH is the same thing but with only -CO2H group.

 

[ShaanSiddiq090909]

Someone please post the link for solved yearly past papers for chem

 

[h4rriet]

How to do this ?View attachment 28899

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

20

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.

 

[darkxangel]

Na reacts with both groups to form ONa- which is charged (-1), there is three so 3 ONa- will form

NaOH is the same thing but with only -CO2H group.

Oh Alright . Thanks

 

[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