Chemistry: Post your doubts here!

[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???

 

[smartangel]

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

umm i dont understand. what exactly are you trying to say?

 

[xxfarhaxx]

umm i dont understand. what exactly are you trying to say?

isnt the bond between Cl-Cl covalent???
n da bond between Cl2-Cl2 vanderwalls????

 

[Nibz]

Assalamoalaikum wr wb!

got some doubts:

Q2. B because ionisation energy decreses. More shielding effect. Hence, easier to remove the outermost electron.

Q.6 D is correct because. In CrO2Cl2 the o.s of Cr is x -4 -2 = 0 so, x = +6 and in Cr2O3 it's o.s is 2x -6 = 0 , x = + 3
Oxidation state from +6 to +3 is reduction.

Q12. SiCl4 + 2H20 -> SiO2 + 4HCl (normal reaction which is in syllabus of Period 3 elements)
SiO2 is white solid (so white ppt) and HCl is acidic so acidic solution.

Q13. P4O10 + Water -> Phosphoric Acid so acidic pH
PCl5 + Water -> Phosphoric acid + Fumes of HCl so acidic pH. Same effect on pH of P.

Q16. ONLY and ONLY TEMPERATURE AFFECTS THE equilibrium constant Kc. Write this somewhere.

Q24. Intermediate is a Carbocation which has a positive charge. Positive charge means electron lover. Electron lover means electrophile.

Q34.
No possibility at all of Sulfuric Acid formation.
Ammonium sulfate + lime water -> Calcium Sulfate + Ammonia

Q15. Magnesium hyddroxide is a base. NH4+ when donates a proton can act as an acid and so option D is correct.

Q31. Net dipole moment at the NH2 groups may become zero at some point when another hydrogen bond is formed between them and so temporary induced dipole arises. Not sure though.

 

[saudha]

PV = nRT
V = nRT/PV

Moles of water used = Mass/Mr = 1/18 = 0.056...

V (in cm^3) = (0.056 * 8.314 * 596) / (101 x 10^3)
V = 2.72 dm^3

So C is right. It's off by a little but the only option close to it is C. Also, remember that you have to use SI units in the formula.

thank you