Chemistry: Post your doubts here!

[Metanoia]

explain followingView attachment 45018 View attachment 45019

Q14.
Group II nitrates decompose based on the equation below:

2 X(NO3)2 (s) --> 2 XO (s) + 4 NO2 (g) +O2(g)

Mass of XO = 1.47 g
Moles of XO = 1.47/ (Mr of X + 16)

Mass of X(NO3)2 = 3 g
Moles of X(NO3)2 = 3/(Mr of X + 124)

since moles of X(NO3)2 = moles of XO
3/(Mr of X + 124) = 1.47/ (Mr of X + 16)

Solve for Mr of X.

Q10
Heat of neutralization for strong acids and strong alkali is estimated to be -57kJ PER MOLE of H2O formed.

For both experiments. (Involving strong acid and bases) , it reflects twos moles of water formed .

So heat of reaction is -57 x 2 for both equations.

 

[Metanoia]

Question 20 please...

Q2o. IF all carbons are single bonds, CnH2n+2O, C20H42O (20 carbons , 42 hydrogen, 1 oxygen)

Since 1 aldehyde group is present, subtract 2 H, C20H40O (20 carbons , 40 hydrogen, 1 oxygen)

Since it contains a ring, subtract another 2H, C20H38O (20 carbons , 38 hydrogen, 1 oxygen)

Since retinal contains only 28 H, the missing 1o H are due to 5 double bonds.

 

[Metanoia]

Q31 : is it PH3 is trigonal planar ? i though it should be trigonal pyramidal ???

PH3 should be trigonal pyramidal.

 

[ZaqZainab]

yes please!

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_11.pdf

Help in q30 please. Cant differentiate between B and D.

Focus on the H atoms across the C=C bonds.
B is trans and D is cis isomer.

 

[Metanoia]

Is carboxylic acid completely soluble in water?

The smaller ones are soluble, but as the alkyl length gets longer (more than 5 C) it gets less soluble.

 

[IGCSE13]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_13.pdf Q29 AnsD Q35 ansC Q36 ansA

 

[Zepudee]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf

Q3(C), 4(D), 21(C) and 25(B)
Need help!

 

[loveyuan]

Which compounds can be obtained from ethene in a
single
reaction?
1 CH3CH3
2 -(- CH2CH2-)-n
3 HOCH2CH2OH

 

[Metanoia]

Metanoia , ZaqZainab , @ Every One , Could u Plz help me with this
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_1.pdf

Q2..Answer B
Q13.Answer B>>>Why it is not Mg ??Mg is just beside Al , so i thought that it will have a similar Electronegativity as Mg.
Q15.Answer C>>>When H2SO4 acts as an acid and when it acts as an oxidizing agent?
Q31.Answer A>>>I know that this is simple, but i am always confused with this type,So is there any hint??
Q32.Answer D
Q33.Answer B
Q40.Answer B

THNX in advance

Q15. When reacted with conc H2SO4
NaCl --> HCl
NaBr --> HBr --> Br2
NaI --> HI --> I2
so H2SO4 oxidises Br- and I-.

Q31. Answer seems to be B instead of A?
Al in AlCl3 has 3 bond pairs, 0 lone pairs. Trigonal planar
C in CH+ has 3 bond pairs, 0 lone pairs. Trigonal planar
P in PH3 has 3 bond pairs and 1 lone pair. Trigonal pyramidal.

Q40. Hydrolyse the ester bond
Left fragment forms structure 1 (carboxylate salt)
Right fragment forms structure 2. (alcohol)

Q32. When temperature keeps increasing, all the mass of solid would eventually become gas. So the mass of gas at the end is the same as mass of solid.
Pressure will keep increasing if temperature increases at a constant volume.

Q33. It depends on which experiment could be carried out in the lab. If not feasible, have to use Hess Law to calculate enthalpy change indirectly.
A. Not feasible as hard to tell if all CuSO4 is hydrated by 5 mols of H2O
B. Not feasible as C(s) + 2H2(g) --> CH4 (g) doesn't occur in lab
C. Feasible, was we can burn a know quantity of glucose and measure temperature rise in calorimeter.

 

[DeViL gURl B)]

For May June 2012 paper variant 11

Please explain
--> q 7 the answer is c
Q 6 the answer is B
Question 13 answer is 13

Q 14 answer is B
Question 38 answer is A

Dunno but found this paper real tough! Please help!!!!

 

[Zepudee]

Which compounds can be obtained from ethene in a
single
reaction?
1 CH3CH3
2 -(- CH2CH2-)-n
3 HOCH2CH2OH

is it A?

 

[Metanoia]

In q32, does the gas partially turn into a liquid too?

Possible. Or they could also remain as gas. The idea is they have attraction forces which causes them to occupy a lower volume than expected. This goes against the assumption that idea gases have no attraction forces among each other.

 

[randomcod]

View attachment 45034

THANKS!!!

 

[ZaqZainab]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Q3 answer is C buts isn't it suppose to be A?
Q20 answer is A
Q23 isn't moles of H2 suppose to be 3?? answer is A
Q28 answer is B
Q33 isnt 3 suppose to be correct too if the activation energy is higher than 500 the reaction wouldnt have even started
Q40 i have no idea answer is C

 

[ZaqZainab]

THANKS!!!

I hope it helped My pleasure

 

[ZaqZainab]

Which compounds can be obtained from ethene in a
single
reaction?
1 CH3CH3
2 -(- CH2CH2-)-n
3 HOCH2CH2OH

A
Ethene,C2H2
1. C2H2--->C2H6
using H2 and Ni
2. Polymerization
3. using cold acidified KMO4

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf

Q16,39

 

[Metanoia]

please help

Q16,24,27,34 of http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf

Q16. Barium carbonate does not dissolve in water, but reacts with acid to form a soluble Ba2+.
BaCl2 is soluble in both water and acid.
Ba(OH)2 soluble in both
BaSO4 insoluble in both

Q24. Steamy fumes with PCl5 means there COULD be OH group, either as OH alcohol or COOH acid. We are not sure which.
Since it does not react with 2,4-DNPH. It must not be ketone or aldehyde.
So the only sure conclusion we can make is its not an aldehyde.

For next 2 questions, I copied from the examiners report, if need be will draw out the structures of Q27

"Q27. The question should be approached by counting the OH groups in the product X. Warm dilute H2SO4 will hydrolyse the
ester link in santonin, producing two OH groups. Cold, acidified KMnO4 will oxidise the two C=C bonds in santonin, producing four more OH groups. This makes six in total."

"Q34
The key to ruling out both A and C is statement 3, ‘X and Y must both be in the same Group of the Periodic Table’. This statement is incorrect, X and Y could be in group 2, or one or both of them could be transition metals."

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_13.pdf Q29 AnsD Q35 ansC Q36 ansA

w12qp13

Q29. Since methanoic acid is used, the alcohol would be butanol.
HCOOC4H9

There are 4 isomers of butanol, so depending on which isomer of butanol we used, we have 4 possible structural isomers of esters.
If we use butan-2-ol, the ester also have a chiral carbon and so an extra opital isomer.
Total: 5 possible isomers. It would be best if you can try to draw the 4 structural isomers and see for yourself which has a chiral carbon.

Q35. W is MgO
X is CaCO3
Y is CaO
Z is Ca(OH)2
Try to see which of the statements makes sense from here, check back here if still unclear.

Q36. J is sulfur, K is SO2, L is SO3
Again, try to see which of the statements makes sense from here, check back here if still unclear.