Chemistry: Post your doubts here!

[XPFMember]

Or removed because the mods can't take a joke...

aoa wr wb!
in that case, you definitely would have received a warning...
Did you?

 

[melly713]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf # 21,#22
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_11.pdf #22,#23
plz help thanx

 

[smartangel]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q27..shouldnt the answer be 2 chiral centres if you consider the 2nd and 3rd carbon from the right!

 

[Nibz]

thank you so much! i got it now! please explain Q17 also.

You're welcome.

Option A is clearly wrong.
Option B not correct becaues H3PO4 is not stronger O.A than Iodine because, from what the table says, it has not oxidised the Iodide (in HI). Same oxidation state as before (in NaI).
For option C, same argument as above.
Option D is correct because Iodine has been oxidised to I2. Oxidation state from -1 to O. So it's a stronger O.A than Iodine.

 

[alphabravocharlie]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q27..shouldnt the answer be 2 chiral centres if you consider the 2nd and 3rd carbon from the right!

no, the 2nd C is bonded to 2[CH2CL], so it is not chiral, only the 3rd one is

 

[Nibz]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q27..shouldnt the answer be 2 chiral centres if you consider the 2nd and 3rd carbon from the right!

No, the second carbon from the right is not chiral. Look closely, and you will see that it has CH2Cl on bottom and right side.

 

[smartangel]

No, the second carbon from the right is not chiral. Look closely, and you will see that it has CH2Cl on bottom and right side.

oh right!! got it! thanks a lot!

 

[smartangel]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q39. how exactly do we work out the answer?

 

[Student12]

Q2.
3 peaks.
1 peak - Cl 35 Cl 35
2 peak - Cl 35 Cl 37
3 peak - Cl37 Cl37

Q 10. N2O4 -> 2NO2
Initila pressures : 100% -> 0%
Pressure at 60 : 50% -> 2 (50%)
Mol ratio(pressure/total pressure) = 50/150 -> 100/150
= 1/3 -> 2/3

Kp = (2/3)^2 / (1/3) = 4/3 atm Answer.C


Q.11

Option B is out of the question, because the reaction involving Chloride ions is not reversible.
Option A is correct because it will move the equilibrium position to the right, hence highest conc. of HOCl.

Q.16
Thermal decomposition of Calcium Nitrate:
2Ca(NO3)2 -> 2Cao + 4NO2 + O2
Solid residue in the product side is CaO only. The rest are gases.
Ca(NO3)2 and CaO are in 1:1
Mol of Ca(NO3)2 = 4.10/164.1 = 0.02498
Mol of CaO = 0.02498
Mol = mass/mr
o.02498 = Mass/56.1
= 1.40 g Answer C

Thank you!
For Q2- what are the other possibilites of such questions coming in the exam ? & When can it be 5 peaks ?

 

[xxfarhaxx]

P1 hlp hlp..urgent!!!
hlp!!!!
12/o/n/10
Q- 10,18,22

 

[Nibz]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q39. how exactly do we work out the answer?

In termination step from bromination of propane the two radicals would be C3H7. & C3H7.
1 is right because the first three carbons from left are from one radical, and the rest on right are from the second one.
2 is right because you can see two radicals clearly.
3 can't be right because, that structure is impossible to be formed from two C3H7. radicals. The methyl group is on the middle carbon. C2H5. and C4H9. radicals are not there in the termination step.
Vague, but I hope it helps.

 

[XPFMember]

Assalamoalaikum wr wb!

got some doubts:

 

[xxfarhaxx]

6.

Q23. not A cz thr r 3 hydrogens bonded to da carbon group.
Not D coz 3 methyl groups r bonded

6. nt B cz nly H2 come close to an ideal gas behaviour in da given options (on the graph nly line Y comes close to an ideal gas) thrfr ans is D.

 

[smartangel]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
in Q6..shouldnt Y be higher as the peak increases when temp is reduced?
and plz explain Q 11, 19,23 as well!

 

[Student12]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
1,4,11,14

 

[smartangel]

7 Which pair of elements have bonds of the same type between their atoms in the solid state?
A aluminium and phosphorus
B chlorine and argon
C magnesium and silicon
D sulphur and chlorine

why is the answer D and not A or B?

 

[geek101]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q2- The answer is B ? explain plz.

see there is Cl2+ which means there are two Cl atoms, for ever peak. So here you have to make combinations....so the peak could either be, 1) Cl-35, Cl-35 2) Cl-37, Cl-37 3) Cl-35, Cl-37
so in total thats 3 possible peaks that could be recorded. hope that helps. good luck

 

[xxfarhaxx]

Assalamoalaikum wr wb!

got some doubts:

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2. A,C,D- all increaes dwn da group

13.D- P4O10 + 6H2O ---> 4H3PO4 (phosphoric (v) acid )
PCl5 + 4H2O ----> H3PO4 + 5HCl (agan phosphoric (v) acid is formed)

16. A- only temperature changes the value of Kc n Kp.

 

[alphabravocharlie]

Assalamoalaikum wr wb!

got some doubts:

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2: Ionic radius inc down the group right, electrons move away from nucleus, nuclear attraction on the outer shell electrons dec, so less energy required to remove elecrons from outer shell, so less ionization energy

6: In every other Cr doesn't undergo anything, its valency remains at 6, only in d it changes from +6 to +3

12: products are SiO2 and HCl

24: Intermediate is a positive, electron loving atom: CH2BrCH2+

 

[xxfarhaxx]

7 Which pair of elements have bonds of the same type between their atoms in the solid state?
A aluminium and phosphorus
B chlorine and argon
C magnesium and silicon
D sulphur and chlorine

why is the answer D and not A or B?

bt doesnt cl from covalent bond between Cl-Cl n vanderwalls force between Cl2-Cl2 like idoine does???