Chemistry: Post your doubts here!

[Jelleh Belleh]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Number 9?? Answer B
Anyone please??

I solved this question by considering each option one at a time.
Option B)
.......2P <=> 2Q + R
I.......2...........0.......0
C....-2x........+2x....+x
E....2-2x........2x......x

2-2x + 2x + x
= 2 + x

 

[Youssef Tawil]

I solved this question by considering each option one at a time.
Option B)
.......2P <=> 2Q + R
I.......2...........0.......0
C....-2x........+2x....+x
E....2-2x........2x......x

2-2x + 2x + x
= 2 + x

Thank you!

 

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w13_qp_11.pdf A
Number 26 Answer is B but why not 4??

 

[$$AK$$]

Do try to include the answers next to your selected questions, it would make it easier for us to reply.

Q8. To find the "heaviest atmosphere", we can use the weighted average of the Mr.
Using option D as example.
Weighted Mr of D
= 0.825 x Mr of H2 + 0.152 x Mr of He + 0.023 x Mr of CH4
=0.825 x 2+ 0.152 x 4 + 0.023 x 16
= 2.63

Work out the other 3 options, the highest one is the most dense.

Q9.

View attachment 44395


Q13.
White precipitate means it forms an insoluble sulfate, which would be barium sulfate.

Q16.
Reaction 1: O.S of sulfur +6 (in H2SO4) --> +6 (in K2SO4), no change
Reaction 2: O.S of sulfur +6 --> +4 (in SO2) , change of 2 units
Reaction 3: O.S of sulfur +6 (in H2SO4) --> -2 (in H2S), change of 8 units

Q17. Ammonium chloride solution is slightly acidic as the NH4+ can donate protons (acidic), so it reacts with the alkaline magnesium hydroxide.

Q20.
1st reaction: oxidation (loss of H)
2nd reaction: nucleophilic addition (the lone pair on OH attracts the slightly positive carbon on the aldehyde)
3rd reaction : oxidation (loss of H)

Thnx man
It was very helpful
Sure,next time i will post the answer

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Help with 39 please! Answer is B, which is I & II.

Check post #9312 on page 466

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf Q3 ans D ,Q26 ansA , Q31 ansA , Q35 AnsB , Q36 ansD Q37 ansD please help if you can

w11qp12

Q3.
Cl- : 1s2 2s2 2p6 3s2 3p6
F- : 1s2 2s2 2p6
K+ : 1s2 2s2 2p6 3s2 3p6
Na+ : 1s2 2s2 2p6

We need to focus on F- and Na+ as the electrons removed are from a shell nearer to the nucleus.
Between F- and Na+, Na+ has more protons, so will hold on to its electrons more tightly.

Q26.
C2H5OH --> CH3CHO (note that aldehyde is collected, not acid)

mass of C2H5OH converted = 2.30 x 0.7 = 1.61 g
moles of C2H5OH converted = 1.61/46 = 0.035 mol
moles of CCH3CHO formed = 0.035 mol
mass of CH3CHO formed = 0.035 x 44 = 1.54 g

Q31.


Q36.
X is actually N2.
X--> Y--> Z
N2 --> NO --> NO2

Q37. C4H10O , note that the C4H10 is following the general formula CnH2n+2, so it means that the carbon are all single bonded. The oxygen atom would be part of an alcohol group and not ketone/aldehyde.

Since not ketone/aldehyde, we will not get observation 1.
If tertiary alcohol, we will get observation 2.
If primary or secondary alcohol, we will get observation 3.

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_11.pdf A
Number 26 Answer is B but why not 4??

w13qp11

4 atoms of H are removed (from 3 COOH and 1 OH).

4H --> 2H2 ( 2 moles of H2 gases)

 

[Browny]

Q5. The molecule is not symmetrical, you have to view it in its 3D shape, it is tetrahedral.

Q6. MgCl2 dissolves, SiCl4 hydrolyses.

Q23. Each carbon has 4 single bonds, they are tetrahedral shape around each carbon.

Q36. NH3 accepts a H+ to form NH4+, it is a proton acceptor (base)

Q39.
H2SO4 (acid) donates a proton to C2H5OH.

Q23, The carbons are in a row like -C-C-C which is 180 right.

I know the bonds are tetrahedral but the C row has a 180 angle right?

 

[Manal.A]

Can anyone pls explain quality mj paper 11 year 2012....how do we find the equilibrium equation

 

[Metanoia]

Q23, The carbons are in a row like -C-C-C which is 180 right.

I know the bonds are tetrahedral but the C row has a 180 angle right?

hmm..this is a bit contradicting, how can it both be tetrahedral and have 180 at the same time?

Carbons in a row doesn't mean 180 degrees..

 

[Gehad Mohamed]

Hi can someone please explain these questions
they are from 9701/11/O/N/12

 

[Browny]

hmm..this is a bit contradicting, how can it both be tetrahedral and have 180 at the same time?

Carbons in a row doesn't mean 180 degrees..

View attachment 44448

OK thanks got it and will you be able to cover at least another 5 years in the coming 5 days in the youtube videos?

 

[$$AK$$]

Guys any tips for solving chemistry p1 ????

 

[FarahMJ]

Help with this one plz, ans is B

 

[Metanoia]

OK thanks got it and will you be able to cover at least another 5 years in the coming 5 days in the youtube videos?

Some years have 3 mcqs, so it depends on the years. I'm working on the 2013 June papers first, then the 2013 Nov papers.

2013 June Paper 12 should be ready (if no uploading issues) by this evening.

 

[kingo44]

Help with this one plz, ans is B

Step 1: Count the hydrogen atoms in the side-chains.
Upper side-chain and lower side-chain: 2 x (3+6+6+14) = 58
Middle side-chain: 3 + 6 + 6 + 14 = 29

Step 2: Count the hydrogen atoms in each residue
First residue: 3 + 8 + 6 + 14 = 31
Second residue x 2 (because two side-chains are converted): 2 x (3 + 14 + 2 + 14) = 66

Step 3: Calculate how many hydrogen atoms had to be added to each side-chain in order to form the residues.
Upper and lower side-chain residues have 66 - 58 extra hydrogens = 8 extra hydrogens
Middle side-chain residue has 31-29 extra hydrogens = 2 extra hydrogens

Step 4: You know that 10 hydrogen atoms have been added to the original molecule. Each hydrogen molecule contains two hydrogen atoms, so there are 10/2 = 5 hydrogen molecules ie. 5 moles of hydrogen

 

[kingo44]

if u need any hel p girl then ask me lol nice pic btw

 

[happyperson]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_34.pdf
Can someone please explain me Q1 part c i, how to calculate the initial concentration. Thanks.

 

[Browny]

Some years have 3 mcqs, so it depends on the years. I'm working on the 2013 June papers first, then the 2013 Nov papers.

2013 June Paper 12 should be ready (if no uploading issues) by this evening.

OK thanks so much!

 

[kingo44]

reallty metanoia awesome moreeeeeeeeee videod