Chemistry: Post your doubts here!

[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.

 

[A star]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_11.pdf Q23

 

[hope4thebest]

w08 qno 38?
How?

 

[Malik777]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf Q9 plz

 

[Malik777]

Can somebody explain those?
View attachment 28900
q23 - What do they mean by mole fraction is 0.5? How does that affect the identity of X?
View attachment 28901
q33 - Why is it 1? Why isn't it 2?
View attachment 28902
q35 -How does nitrogen undergo a redox reaction? It only goes from +3 to 0.
View attachment 28904
q31 - Where do ionic bonds form? All elements present are non metals?

q31 answer is C ? :S

 

[Jiyad Ahsan]

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

umm its not an option.. i asked my teacher the samething, he said that we have to think of the acid as a limiting agent..

 

[HubbaBubba]

q31 answer is C ? :S

Nope it's B.
Sulfur trioxide is acidic, and ammonia is a base so that's an acid-base reaction. If you check the equation no oxidation or reduction takes place in any of the elements.

 

[LimeReem]

15 Use of the Data Booklet is relevant to this question.
The combustion of fossil fuels is a major source of increasing atmospheric carbon dioxide, with a
consequential rise in global warming. Another significant contribution to carbon dioxide levels
comes from the thermal decomposition of limestone, in the manufacture of cement and of lime for
agricultural purposes.
Cement works roast 1000 million tonnes of limestone per year and a further 200 million tonnes is
roasted in kilns to make lime.
What is the total annual mass output of carbon dioxide (in million tonnes) from these two
processes?
A 440 B 527 C 660 D 880

 

[Jiyad Ahsan]

Q4..

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

add all the electrons..
3 x 8 from oxygen
6 from carbon
1 from hydrogen
1 because its an anion (negatively charged.. so must have an excess electrons, and since it requires 2 anions to react with Ca its must be -1)
adding up we have 32, so answer is C

 

[Jiyad Ahsan]

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

Q5
the answer is D, since when the difference between molecules of a liquid and a gas is the forces holding the liquid molecules together so, in this case hydrogen bonding
so just vaporize a mole of liquid hydrogen halide and note down the energy change that would also be an indicator to the strength of the (hydrogen)bonds

 

[Raiyan3]

Can somebody explain those?
View attachment 28900
q23 - What do they mean by mole fraction is 0.5? How does that affect the identity of X?
View attachment 28901
q33 - Why is it 1? Why isn't it 2?
View attachment 28902
q35 -How does nitrogen undergo a redox reaction? It only goes from +3 to 0.
View attachment 28904
q31 - Where do ionic bonds form? All elements present are non metals?

For question 23
"Ethene is half of the products. So there must be 2 ethene molecules and 1 propene and methane. 3+1+(2x2)=8. The compound that is cracked must contain 8 carbons."
For question 33.
Option number 2 is wrong because that is the wrong equation. Because pV=nRT (n=moles) not pV=MRT (M=molar mass)
For question 35
Im little bit confused aswell. Btw Nitrogen goes from -3 to 0 cause its more electronegative the Cl. Hope that helps a little.

 

[Malik777]

Nope it's B.
Sulfur trioxide is acidic, and ammonia is a base so that's an acid-base reaction. If you check the equation no oxidation or reduction takes place in any of the elements.

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf Q9 plz :/

 

[Jiyad Ahsan]

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

Alice there were the other ways as well
and you dnt have to say i did it i aint gonna sue you!

 

[hope4thebest]

Q5
the answer is D, since when the difference between molecules of a liquid and a gas is the forces holding the liquid molecules together so, in this case hydrogen bonding
so just vaporize a mole of liquid hydrogen halide and note down the energy change that would also be an indicator to the strength of the (hydrogen)bonds

what about question 34 in may june 07? Thanks

 

[bital]

Can somebody explain those?
View attachment 28900
q23 - What do they mean by mole fraction is 0.5? How does that affect the identity of X?
View attachment 28901
q33 - Why is it 1? Why isn't it 2?
View attachment 28902
q35 -How does nitrogen undergo a redox reaction? It only goes from +3 to 0.
View attachment 28904
q31 - Where do ionic bonds form? All elements present are non metals?

Can you please tell what papers are these from?