Chemistry: Post your doubts here!

[syed1995]

Assalamu Alikum Wa Rahmatullahi wa Barakatoho.
Can anyone explain Question 9 please. syed1995
How to solve it.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf

Honestly my concept on this one isn't much clear.. but from what I have seen on XPF.

m1 = 0.05 x 0.1 = 0.005 mol/dm^3 for the metal

m2 = 0.025 x 0.1 = 0.0025 mol/dm^3 for sodium

We know that sodium's oxidation number is +1

We divide m1 by m2

0.005/0.0025 and multiply by the oxidation number of sodium.

2*1 = +2 Answer is B

 

[PhyZac]

Honestly my concept on this one isn't much clear.. but from what I have seen on XPF.

m1 = 0.05 x 0.1 = 0.005 mol/dm^3 for the metal

m2 = 0.025 x 0.1 = 0.0025 mol/dm^3 for sodium

We know that sodium's oxidation number is +1

We divide m1 by m2

0.005/0.0025 and multiply by the oxidation number of sodium.

2*1 = +2 Answer is B

Thanks alot....Jazaka Allah khairan...May Allah S.W.T have mercy on you and your family, and shower His blessing upon you Aameen.
The thing is...i see your answer is correct, though i dont feel the way is right...it might be..but i jst dont get it..Very Sorry

 

[syed1995]

N 2011 q13 q24 q29 q30 q31 q34 q37 q38 q39

Can u plz solve these questions for me??

29
The answer will be D. since it is saying Methylpropene .. that can only be made from a molecule with (CH3)2 since it will be branched.
30
C4H8
C-C=C-C
1 only.. since all others will have 2 H attached to the C.
31 A 1 and 3 are correct cuz of lone pairs and same no. of e clouds.. I am not sure of 2 but since the only choice with 1 and 3 is A.. the answer is A.
34 D 1 is correct .. 2 is wrong cuz group 2 are partially soluble.. 3 is wrong as well since reactivity increases down the group and it will react with cold water..
37 D .. Don't know about how 1 and 3 are not possible.. just know that 2 is possible with an ether C2H5OC2H5 which won't oxidize or react with DNPH or Tollens so the only possible answer is D. EDIT 3 is also not possible.. since oxidation of an alcohol always gives an carbonyl group which will react with DNPH so both 2 and 3 are incorrect.
39 C .. 1 is wrong.. with NaOH (aq) it will become an alcohol but that's it.. 2 is correct .. it will be the reverse of ester .. ester + water (from dil. acid) + H2S04 --> Alcohol + Carboxlic acid 3 is correct as well .. CN gives COOH with reaction with a mineral acid.

 

[syed1995]

Thanks alot....Jazaka Allah khairan...May Allah S.W.T have mercy on you and your family, and shower His blessing upon you Aameen.
The thing is...i see your answer is correct, though i dont feel the way is right...it might be..but i jst dont get it..Very Sorry

Yea.. I don't get the logic behind it either. But someone else on XPF solved it this way.. I will be asking my teacher about this one tomorrow.. and let you know how this one is solved.

 

[PhyZac]

Yea.. I don't get the logic behind it either. But someone else on XPF solved it this way.. I will be asking my teacher about this one tomorrow.. and let you know how this one is solved.

Oh okay, yea sure, In Sha Allah we will get it.

 

[iKhaled]

ohh okay -_- yeah i got u now.... gosh i cud just blow up organic chem if i got the chance!! every question seems to be an alien !! -_- x.x
Thankss btw for ur help... i'll b needing a lot of it especially in the organic section over the next couple of days ^_^

no problem ask me whenever u want and i will do my best to help you get the answers of ur questions !

 

[Es Jay]

could someone try solving this? There is no marking scheme for this paper :/

 

[Warrior66]

could someone try solving this? There is no marking scheme for this paper :/
View attachment 23911

Asalam-o-Alaikum!
which year is this paper?
proceeding down the table: (i think these are the correct answers.)
1. A & B
2. E
3. E
4. C
5. C & D
6. E

 

[darknessinme]

Assalamu Alikum Wa Rahmatullahi wa Barakatoho.
Can anyone explain Question 9 please.
How to solve it.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf

n(sulphite)=0.0025mol and n(metal)=0.005mol
So ratio of metal(M3+):sulphite is 2:1
Half equation for sulphite:
SO32- + H2O→SO42- + 2H+ + 2e-

The half equation of the metal must have two moles of the metal and it also has to have 2e-. So just balance this equation to get:
2M3+ + 2e- → 2M2+

So ox. no of metal is +2

 

[daredevil]

Heey everyone. Can anyone plz post the er of w2011 for chem?! i cudnt fint it in the papers section of xtremepapers. Thanks

 

[daredevil]

I think

could someone try solving this? There is no marking scheme for this paper :/
View attachment 23911

Warrior66 gave the ryt answers buy still can u confirm it?? and yeah which paper is this?

 

[PhyZac]

n(sulphite)=0.0025mol and n(metal)=0.005mol
So ratio of metal(M3+):sulphite is 2:1
Half equation for sulphite:
SO32- + H2O→SO42- + 2H+ + 2e-

The half equation of the metal must have two moles of the metal and it also has to have 2e-. So just balance this equation to get:
2M3+ + 2e- → 2M2+

So ox. no of metal is +2

Thanks ALOOOT JazkaAllah Khairan...!! May Allah S.W.T reward you Aameeen..!! May Allah Have mercy on you and your family, and grant you the highest grades in this world and hereafter . Ameen...!! Thanks again!!

 

[PANDA-]

Quoting the question...

X(g) ⇄ Y(g) +2Z(g)
10.2 moles of X were heated to temperature 2000°C until equilibrium was established under a total pressure of 8x10^7 Pa. At equilibrium, only 20% of X dissociated. Calculate Kp.

 

[daredevil]

Quoting the question...

which paper is this question of?? like p2 or 4 or 5??

 

[syed1995]

could someone try solving this? There is no marking scheme for this paper :/
View attachment 23911

1. A and B and C
2. C and E (I thought this one was E only though)
3. E
4. C
5. C and D
6. E

Here's the marking scheme

 

[syed1995]

Quoting the question...


X(g) ⇄ Y(g) +2Z(g)
10.2 moles of X were heated to temperature 2000°C until equilibrium was established under a total pressure of 8x10^7 Pa. At equilibrium, only 20% of X dissociated. Calculate Kp.

I don't know how to solve this one.. sorry but i will try

Px = 1/4 * 8x10^7 Pa .. Px = 2x10^7 Pa
Py = 1/4 * 8x10^7 Pa .. Py = 2x10^7 Pa
Pz = 2/4 * 8x10^7 Pa .. Pz = 4x10^7 Pa

[PY * (Pz)^2 ]/Px
(2 x 4 / 2) x 10^7 = 4 x 10^7 Pa

 

[hassankhan]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf

Some one plz help me with these questions
Q6, Q11, Q12, Q13, Q19, Q22, Q26, Q29 and Q38
i knw these are lots but i m unable to understand chem properly

 

[Muhammad Bin Anis]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf

Some one plz help me with these questions
Q6, Q11, Q12, Q13, Q19, Q22, Q26, Q29 and Q38
i knw these are lots but i m unable to understand chem properly

Q6. B ... the curve moves left and upwards...so X has a higher value and Y and Z have lower
Q11 . C ... calculate the number of moles of CO2 produced, that comes out to be 0.003. choosing option C, you use 0.001 moles of the aluminum compound and that gives you a simple ratio of 1:3. trying others give you ratios not in simple forms.
Q12. B... the electronegativity increases across the period and up the group. Going back from aluminium to Magnesium reduces the e.n value , but then moving up to beryllium increase it... thus you get e.n value similar to that of aluminium
Q13. D.. Elements of Group 1 end with electronic configuration ns1, those of group 2 ns2, grp 3 np1, grp 4 np2, grp 5 np3, grp6 np4, grp 7 np5, group 0 np6.
Q19. A ... because oxygen is -2, so H and Cl have to be +1.
Q22. marking scheme says C but i think it should be D

 

[PANDA-]

which paper is this question of?? like p2 or 4 or 5??

This is a paper 2 question.

 

[PANDA-]

I don't know how to solve this one.. sorry but i will try

Px = 1/4 * 8x10^7 Pa .. Px = 2x10^7 Pa
Py = 1/4 * 8x10^7 Pa .. Py = 2x10^7 Pa
Pz = 2/4 * 8x10^7 Pa .. Pz = 4x10^7 Pa

[PY * (Pz)^2 ]/Px
(2 x 4 / 2) x 10^7 = 4 x 10^7 Pa

The unit I believe should be Pa^2 ... Since the way to find the unit of Kp is using the formula of Kp value, but substituting Pa...

[Pa*Pa^2]/Pa ... Pa^2. However, the value of Kp, that I don't know.