Chemistry: Post your doubts here!

[Youssef Tawil]

ok,
according to the data,

the equation of the reaction is.
PbCl4 +4NaBr-->Pb+2Br2+4NaCl.

now
6.980g of PbCl4
calculate its moles,Mr=349
6.980/349
=0.02mol

now since mol ration is 1:2,
we have 0.04mol of Bromine.

to get the mass.
multiply moles with its mr
= 0.04X79.9
=3.196
^ your answer.

you did something wrong , the equation of reaction is PbCl4 +2NaBr--> Pbcl2+Br2+ 2NaCl.
moles of PbCl4 is 6.98/349= 0.02
1:1 ratio = 0.02 mole of Br2
multiply 0.02 by mr of Br2 = 0.02X(79.9+79.9)= 3.196

 

[ahmed faraz]

Srry man
Tom morning i will do the paper, So can i answer ur Q tom PLZ??!

ok !

 

[Exo_luhan]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Q27 PLZ EXPLAIN WHY CANT B be the answer

 

[..sacrifice4Revenge..]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf

q22,
is C, y not B?


and q40.
explain plz

 

[chishtyguy]

Oct/Nov 2012 variant 11
Guys please explain question 17 the answer is D
Q 11 answers 11 answer is A

Q 10 answer is C
Question 15 answer is B
Question 4 answer is A ?? How??
Please full explanation needed!!

Q4 A
N2+O2 > 2NO
Bond Energy (994 496)
Bond energy= Bond Breaking - Bond Form
rearrange it as Bond form= (994+496)- 180
U will get 1310 J that is for 2 molecules
And for 1 molecule 1310/2= 655

Q10
U have to make a born cycle in these kinds of question

use the formula -158-1560= 3(-268) + 2x
x=-430

Q11
Use the definition
Bond energy for the covalent bond (molecule) is the energy required to separate it in to it's constituent (atoms) all of them in gaseous state.... My wordings might not be correct... Only A confirms it

Q 15
Bit tricky
Use the equation X(NO3)2 -> XO + 2NO2+ .5 O2
if we have 2 g of reactants and 1.32 g of gases so XO will be .68
molar ratio of X(NO3)2 : XO = 1:1
now use the formula 2/(X+124) = .68/( X+16)
X is 40 that is the Ar of C

Q 17


eq 2X + O2 -> X2O
Reject A and B
now moles of O2 we know that 1mole = 24000cm3
so O2 is 300/24000=.0125
X should have same number of moles of if we take sodium than moles of 2X = 1.15/23
X= .0125 so answer is Na

 

[..sacrifice4Revenge..]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Q27) Ans is C Howwwwwww? Plz HElp

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Q27 PLZ EXPLAIN WHY CANT B be the answer

+1 to this.
anyone, help plz.
why not B?

 

[chishtyguy]

Man i have practiced most of P1 chemistry and still i am scoring in 20's :s
In p 21 , I think thatr i willlose 20 marks due to my silly mistakes in the silly questions
In p 32, i can lose up to 7-8 marks
so in P11,I need a high score to get an overall A incase{and for sure} the gt is high
Any way thanks man..and sure I will never lose hope...Inshallah Allah will help me
Allah kareem

Hmmmm...You have very little time left... Do u have David Ecaster,Chemistry Book... If u have Then revise maximum topics... Just try to clear as much concepts as u can... Revise ol pst paper and don't worry about the marks... Just try to clear ur concepts up... insha Allah u will do great...

 

[GCE As and a level]

Hmmmm...You have very little time left... Do u have David Ecaster,Chemistry Book... If u have Then revise maximum topics... Just try to clear as much concepts as u can... Revise ol pst paper and don't worry about the marks... Just try to clear ur concepts up... insha Allah u will do great...

U mean david Acaster. Roger Norris, Lawrie Ryan BOOK ?? Orange cover??!
I revise it,i am still scoring from 25 - 29
Thnx man
Inshallah i will

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Q10(B),25(C),28(D)

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf

Q28(B),31(B)

 

[Ahmed Aqdam]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Q27) Ans is C Howwwwwww? Plz HElp

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Q27 PLZ EXPLAIN WHY CANT B be the answer

+1 to this.
anyone, help plz.
why not B?

In the actual ion, CH3 is attached to O from CO2 but in this arrangement it is attached to the C from CO2 so orientation is not correct and ion is different.

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Q10(B),25(C),28(D)

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf

Q28(B),31(B)

Q10:
all the basic stuff: oxygen is more electronegative than Cl and carbon.
in C the dipoles of O and Cl will cancel a little but out to leave a smaller overall dipole. in B it is not the case. C=O means carbon has other groups bonded to it which can share it's charge. o
Q25
in the transition state the OH would have bonded to C but the Cl would have been removed -- yet. overall it will have a negative charge as OH ion had a negative ion. exampleNu represent OH ion)


Q28
a very rough diagram:

 

[_Ahmad]

Q10:
all the basic stuff: oxygen is more electronegative than Cl and carbon.
in C the dipoles of O and Cl will cancel a little but out to leave a smaller overall dipole. in B it is not the case. C=O means carbon has other groups bonded to it which can share it's charge. o
Q25
in the transition state the OH would have bonded to C but the Cl would have been removed -- yet. overall it will have a negative charge as OH ion had a negative ion. exampleNu represent OH ion)
View attachment 45070

Q28
a very rough diagram:
View attachment 45071

THANKS ALOT!!!

 

[Ahmed Aqdam]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf

q22,
is C, y not B?


and q40.
explain plz

22: In B it will form CH2OHCH2OH so H and OH are not in correct ratio and it is saturated anyway so it will not be polymerised.

40:

40: A would mean polymer has same number of molecules as monomer and would be identical to it so not possible.
If all 6.02x10^23 molecules react, it will form one molecule but 1/6.02x10^23 moles.

I'll just add on to Q40 since Ahmed Aqdam has addressed the other questions.

Q40. Requires a bit of reasoning, if 1 mole of monomer join together, we will get less than 1 mole of polymer.
If we end up with 1 mole of polymer in the end, it means none of the monomer has joined to any other!

Its like 1000 bricks (monomer) will build one house (polymer) , the number of monomer is expected to be more than polymers.
Hope it makes sense.

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf

Q28(B),31(B)

Q28
This kind of diagram only appears if there were two steps. in one step a less stable intermediate product was made which was then converted into another product. such as CH2CH2Br --> CH2CH2(positive) + Br(negative) and then an attack by, say, OH(negative)
this does not happen in Sn2 reaction where there is a transition state but no intermediate products. Sn2 reaction happen with primary halogenoalkanes. secondary can have both.
All other reaction have an intermediate. so (B) is answer.
Q31
you must be having problem why (3) is wrong. actually the T in the equation is in kelvin. so the temperature does not double but actually increase by 25. so it is wrong. to double it the temperature must double means 2X(273+25=596K=323°C
All others are correct. if you want to know how ask me freely.

 

[SIstudy]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Q10(B),25(C),28(D)

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf

Q28(B),31(B)

See Q31 is B cuz the 3rd statement is completely incorrect, according to ideal gas law
gas molecules have negligible vol
so temp shouldn't really affect the vol here
and the other questions are my doubts as well :/

 

[Suchal Riaz]

THANKS ALOT!!!

if you still have any confusion ask freely.

 

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Number 20? answer is A how do u know the number of carbon double bonds?

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf

Q4(C),9(D),39(C)

 

[Ahmed Aqdam]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Number 20? answer is A how do u know the number of carbon double bonds?

If all are single bonds then total hydrogen 42 according to the general formula: CnH2n+2O.
1 aldehyde so 2 less H. 1 ring so another 2 less H. Remaining H are 38.
5 double bonds as for every double bond, 2 less H. So remaining are 28.

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Q10(B),25(C),28(D)

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf

Q28(B),31(B)

and one more thing. in question 31 (2) statement is correct because density is proportional to n/V and rearranging equation we get n/v = p/(RT) which shows inverse relation.