Chemistry: Post your doubts here!

[amina1300]

https://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_12.pdf
Q15 Shouldnt the answer to this be D?
Cl +7 O -8 overall -1 ??

 

[Dukula Jayasinghe]

https://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_12.pdf
Q11

Well, lets look upon (D) first, shall we?
Now when the tap B is open, what will happen is pressure decreases as well as N2 concerntration decreases cos Li+N2 will occur. Position of equilibrium shifts to the left, causing % of NH3 to decrease. (D) is wrong.
Looking upon (C)
When A is open, pressure decreases, yield of ammonia decreases as position of equilibrium shifts to the left.
Looking upon (B)
When both are open, oh my god, the pressure will be even lower,....
Looking upon (A)
Now this is the answer. This is because pressure is higher so position of equilibrium is shifted to RHS so % of ammonia increases

 

[amina1300]

https://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_12.pdf
Q20 why isn't the answer D?

 

[Dukula Jayasinghe]

https://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_12.pdf
Q15 Shouldnt the answer to this be D?
Cl +7 O -8 overall -1 ??

NO. you must know this equation
WHEN CHLORINE REACTS WITH HOT CONCERNTRATED NAOH
6NaOH + 3Cl2 --> NaClO3 + 5NaCl + 3H2O
When chlorine reacrs with cold aquos NAOH
2NaOH + Cl2 --> NaClO + NaCl + H2O
According to answers givn
(C)

 

[Mstudent]

BTW

volume of M = V
volume of N = 3 V.
Total volume = 4V.
P1V1=P2V2.
(1 x 10^5)(V)=P2(4V)
P2 = 25000 Pa

Change in temp ; 20 to 100 degree Celsius.
New pressure P2/T1=P3/T2.
25000/293=P3/373
Hence, P3 is 3.18 x 10^4 Pa.

BTW there is an easier way.

USE this : [P1V1]/T1 = [P2V2]/T2 and put in the values you put in. Much quicker and less hassle!

hope this helped you

 

[Dukula Jayasinghe]

https://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_12.pdf
Q20 why isn't the answer D?

The answer should be C.
This is because of the Markonokov addition principle of alkenes. It states that when a H-X (where X can be any halogen) reacts with an alkene, the X shoould go and bond with the carbon containg more alkyl groups attatched to it. This can be seen in the mechanism. During the mechanism, a carbo cation is formed which makes it relatively unstable, so to make it stable, the H should go and bond with the carbon containg lower alkyl groups to make more alkyl groups bonded to the carbocation which will reduce the charge density of it and hence, finally, making it stabiluzed.

 

[amina1300]

https://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_12.pdf
In Q 26 how is the answer C and not B?
Doesn't B make more sense?
Q 30 Arent both all 4 the same?
Q 35 I dont understand the % decrease in mass statement (2)

 

[amina1300]

The answer should be C.
This is because of the Markonokov addition principle of alkenes. It states that when a H-X (where X can be any halogen) reacts with an alkene, the X shoould go and bond with the carbon containg more alkyl groups attatched to it. This can be seen in the mechanism. During the mechanism, a carbo cation is formed which makes it relatively unstable, so to make it stable, the H should go and bond with the carbon containg lower alkyl groups to make more alkyl groups bonded to the carbocation which will reduce the charge density of it and hence, finally, making it stabiluzed.

THANKYOUUU VERY MUCH! !!!!

 

[insharah]

Your answer is correct, but if you look in the Data Booklet, In the Bond Energies section in polyatomic molecules section: there are different values for C double bond C and C Double Bond C in CO2.

It depends on booklet to booklet. old booklet which is used for papers 2016 below have only one bond energy value for carbon=carbon bond which is 740 and the new booklet which is used for papers above 2016 has two bond values 740 and 805

and ur question is from 2013 paper so they assumed the bond value as 740
thats y they got -688 kj per mole
hope this helped you

 

[sarmadimran]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_11.pdf
q27 why ratio is 3:1?

 

[Mstudent]

It depends on booklet to booklet. old booklet which is used for papers 2016 below have only one bond energy value for carbon=carbon bond which is 740 and the new booklet which is used for papers above 2016 has two bond values 740 and 805

and ur question is from 2013 paper so they assumed the bond value as 740
thats y they got -688 kj per mole
hope this helped you

OH, I didnt know about this, thanks for informing me about it!!

 

[Mstudent]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf
q27 why ratio is 3:1?

The formula for propane is CH3CH2CH3, so chlorine can replace each hydrogen atom in ch2 or each hydrogen atom from the two ch3 groups. so the chances of chlorine replacing two hydrogens in ch2 is 2 (2 hydrogens) and 6 for the two ch3 groups (6 hydrogens)

6/2 = 3/1

 

[insharah]

https://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_12.pdf
Q15 Shouldnt the answer to this be D?
Cl +7 O -8 overall -1 ??

remember this equation
CHLORINE IN HOT ALKALI
3CL2+6NaOH-->5NaCL+NaCLO3+3H20

so according to ur question one CL- WHICH IN THIS EQUATION IS NaCL and the other product will be NaCLO3 WHICH IS CLO3- in ur question
HOPE IT HELPED

 

[insharah]

OH, I didnt know about this, thanks for informing me about it!!

welcome

 

[Brisingr]

may 02-NO-2,6,8,21,30,34,39 do help me please THANKYOU

 

[Mstudent]

may 02-NO-2,6,8,21,30,34,39 do help me please THANKYOU

Plz post the qp cuz i cant find it anywhere!

 

[Holmes]

volume of M = V
volume of N = 3 V.
Total volume = 4V.
P1V1=P2V2.
(1 x 10^5)(V)=P2(4V)
P2 = 25000 Pa

Change in temp ; 20 to 100 degree Celsius.
New pressure P2/T1=P3/T2.
25000/293=P3/373
Hence, P3 is 3.18 x 10^4 Pa.

Thanks .
By the way, what is this formula P2/T1=P3/T2.
Can you tell me.
Thanks again

 

[Holmes]

N2(g) + 3H2(g) 2NH3(g)
N2 = 7.2g/6dm3 = 1.2 mol/dm3
H2 = 12g/6dm3 = 2 mol/dm3

Kc= (NH3)^2/((H2)^3*(N2))
6*10^-2= x^2/ (2^3* 1.2)
x=0758=0.76 which is B

Live long amina1300

 

[anastasia grey113]

may 02-NO-2,6,8,21,30,34,39 do help me please THANKYOU

q2
the eq will be CH2O -> H2O + CO2
first find the number of moles of carbs digested
Mr of CH2O = 30
moles = 1.8/30 = 0.06
using mole ratios the number of moles of CO2 r also 0.06
to calculate mass of CO2 multiply the number of moles by CO2 molar mass
thatll be 44 x 0.06
the answer will be 2.64 i.e D

q6 is a bit tough for me too

q8
for enthalpy change of formation of CO2 the equation is
C + O2 -> CO2
n for enthalpy change of combustion of carbon it is the same equation so both the enthalpy changes r for same reaction n must be equal
so its A

q21
1- C2H5Cl
2- C2H4Cl2 (these should be 2 cuz it may be dichloromethane or 1,2- dichloromethane)
3- C3H3Cl3 (same goes for this...all Cl may be attached to one C only or there may be 2 atached to 1 C n 1Cl to the other C)
4- C2H4Cl2 (same is the case with this)
5- C2H5Cl
6- CCl6
so as 3 compounds have two structural isomers the total should be 9.
answer is C.

q30
its an ester so the COO bond will be broken to give one alcohol n one acid
the side linked to C=O will break to form COOH so the acid formed will be HCOOH
while the side linked with O-C will become an alcohol
so the answer is D

 

[amina1300]

Thanks .
By the way, what is this formula P2/T1=P3/T2.
Can you tell me.
Thanks again

P3 is the final pressure and P2 is the answer I got before. I just set up a variables.

The real formula is p1V1/T1 = p2V2/T2 Mstudent says that this gives a correct answer too but I couldn't get one so, I did P1V1 = P2V2 1st and then P2/T1 = P3/T2 (T2 being the new temperature) It just made more sense to me.