Chemistry: Post your doubts here!

[hela]

Please help with the following questions:
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Q23 Q36
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Q13 Q22
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q10

Please help with the following questions:
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Q23 Q36
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Q13 Q22
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q10
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q 20

 

[hela]

Please help with the following questions:
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Q23 Q36
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Q13 Q22
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q10

Please help with the following questions:
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Q23 Q36
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Q13 Q22
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q10
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q 20​

 

[daredevil]

Please help with the following questions:​

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf ​

Q23 Q36​

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

Q13 Q22​

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q10​

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q 20​

i just got around to Q 36.
look if it is Nitrogen or Sulphur then all three options ought to be correct.
because they have told us that it is polutant gas so we know it will be an oxide of N or S.
if one more O is added to the molecule (the molecule is oxidised) then the oxidation number definitely increases by to :-
NO + O --> NO2 ox no. of N increases from 2+ to 4+
SO2 + O --> SO3 ox no. of S increases from 4+ to 6+

no matter if it is N or it's S .... the molecule will definitely have an unpaired electron in both the cases because not all valence electrons bind in S or in N.

as Y is a molecule of N/S and O so two different elements means it is polar. due to the electronegativity difference.

 

[Rahma Abdelrahman]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Please help with the following questions:
Q12
Q26, why 6 isomers, why not 5?
Q29 (If u can explain it here , if not no problemo )
Q30, Why answer is A and not B?
Q35.... In the first sentence, how does N undergo REDOX rx. ?? I guess it is only oxidised as oxidation state increases from -3 to zero
Thanks in advance..

 

[Rahma Abdelrahman]

Please help with the following questions:
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Q23 Q36
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Q13 Q22
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q10
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q 20

Q23--> I did this question just yesterday... They said the mole fraction of ethene is 0.5 meaning ethene is half of the products.. So if there are 8 C atoms, 4 must be from ethene and 4 are from methane and propene ..
If there are 6 C, then 3 must be ethene, then only 3 will remain from the six.. which is not possible as methane and propene together have 4 C atoms.. try like this for the others as well.. Answer is B
Q36 Explained
Q13--> Sorry no idea A small guess may be that as CO2 is produced twice, there shd be 2 compounds with carbonate.. so it's C or D But I don't know why it is C not D..
Q22--> I also have a problem with this question.. there was a similar one somewhere but i couldn't solve either.. I think you got an answer that is not in the choices.
Q10--> enthalpy change of neu. is same because NaOH and Ba(OH)2 are both strong alkalis while HCL and H2SO4 are both strong acids..
Similar to June 2012 P11 Q13 above (That I have no idea about )

 

[ahmed abdulla]

for question 8 u need to do a hess cycle diagram which will look like this....

the values of 590 and 1150 are the first and second ionisation energies!

for question 28 the answer is B because if u can see when we write skeletal formulas we dont include the hydrogen attached on the carbon. the only one that has that is B!

bro .. i posted the WRONG year !
its 2004 .. sorry for that ... http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s04_qp_1.pdf
q8 .... i kept thinking from wr the calcium any way can u help me out with this

 

[iKhaled]

bro .. i posted the WRONG year !
its 2004 .. sorry for that ... http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s04_qp_1.pdf
q8 .... i kept thinking from wr the calcium any way can u help me out with this

haha anyway its okay..

question (8)

you will need to make a hess cycle..see the enthalpy change of formation is when one mole of a compound is formed from its elements int heir standart conditions under standard conditions so we have formed one mole of aluminium oxide and 3 moles of iron (iii) oxide so here is the cycle

question 28

see u have been given 2 hints here. 1 is that that the compound is unreactive to oxidising agents and 2 is that it has been dehydrated so obviously its a third alcohol..now look at the compound which had a hydroxyl group attached to a carbon which is attached to 2 other carbons and the only compound which has this is D! because if u remove the double bond and add the H and OH instead u will see that the OH is tertiary..did u get it ?

 

[iKhaled]

yep bro!
thanks

anytime

 

[ahmed abdulla]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s05_qp_1.pdf
q 2 ..

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_1.pdf
q 2 ..

B!

2 mols of NaN3 give 2 mols of Na and 3 mols of N2

So, 1 mol of NaN3 will give 1 mol of Na and 1.5 mol of N2

10 mol of Na gives 1 mol of N2
So 1 mol of Na will give 0.1 mol of N2

Hence total N2 given is 1.6mol

 

[AbbbbY]

Is the unit for 1000/reaction time in seconds , s^-1 or 1000s^-1 ?

s^-1

 

[Rahma Abdelrahman]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Please help with the following questions:
Q12
Q26, why 6 isomers, why not 5?
Q29 (If u can explain it here , if not no problemo )
Q30, Why answer is A and not B?
Q35.... In the first sentence, how does N undergo REDOX rx. ?? I guess it is only oxidised as oxidation state increases from -3 to zero
Thanks in advance..

Please someone reply! This is the third time I post these doubts

 

[ahmed abdulla]

B!

2 mols of NaN3 give 2 mols of Na and 3 mols of N2

So, 1 mol of NaN3 will give 1 mol of Na and 1.5 mol of N2

10 mol of Na gives 1 mol of N2
So 1 mol of Na will give 0.1 mol of N2

Hence total N2 given is 1.6mol

but didnt they say for NaN3 .. ? y we used the total moles produced of N2 ?

 

[AbbbbY]

but didnt they say for NaN3 .. ? y we used the total moles produced of N2 ?

It's a chain reaction so you have to consider both products since they're happening simultaneously. Getit?

 

[ahmed abdulla]

It's a chain reaction so you have to consider both products since they're happening simultaneously. Getit?

yep

 

[ahmed abdulla]

can someone help me with HESS LAW ... i always get stuck here in drawing , in getting answers ? ...

Q ) Iodine trichloride, ICl3, is made by reacting iodine with chlorine.
I2(s) + Cl2(g) → 2ICl(s) ; ΔH o = +14 kJ mol–1
ICl(s) + Cl2(g) → ICl3(s) ; ΔH o = –88 kJ mol–1
By using the data above, what is the enthalpy change of the formation for solid iodine trichloride?
A –60 kJ mol–1
B –74 kJ mol–1
C –81 kJ mol–1
D –162 kJ mol–1

AbbbbY

 

[AbbbbY]

can someone help me with HESS LAW ... i always get stuck here in drawing , in getting answers ? ...

Q ) Iodine trichloride, ICl3, is made by reacting iodine with chlorine.
I2(s) + Cl2(g) → 2ICl(s) ; ΔH o = +14 kJ mol–1
ICl(s) + Cl2(g) → ICl3(s) ; ΔH o = –88 kJ mol–1
By using the data above, what is the enthalpy change of the formation for solid iodine trichloride?
A –60 kJ mol–1
B –74 kJ mol–1
C –81 kJ mol–1
D –162 kJ mol–1

AbbbbY

ΔHf = ΔHp - ΔHr


You don't need the Hess Law for this.

Since enthalpy of formation is formation of 1 mol from constituent elements (which is a two-step reaction in this case)

So, ΔHf for 2ICl = +14, so ICl = +7

Add that to the second step you have your enthalpy change (In that, -88+7 = -81 thus C)

Wait a few mins I'll upload a handout on Hess's Law. It's very very easy.

 

[AbbbbY]

can someone help me with HESS LAW ... i always get stuck here in drawing , in getting answers ? ...

Q ) Iodine trichloride, ICl3, is made by reacting iodine with chlorine.
I2(s) + Cl2(g) → 2ICl(s) ; ΔH o = +14 kJ mol–1
ICl(s) + Cl2(g) → ICl3(s) ; ΔH o = –88 kJ mol–1
By using the data above, what is the enthalpy change of the formation for solid iodine trichloride?
A –60 kJ mol–1
B –74 kJ mol–1
C –81 kJ mol–1
D –162 kJ mol–1

AbbbbY

These three should cover AS and A2 energetics sufficiently. If you don't get it, let me know what you don't get and I'll explain.

 

[omarjaved619]

HELLLPPPPP!

S12_qp11 Question 1
Why is the answer BF3 and NOT CH3-? :S

And same paper, question 14. Thanks a ton!

 

[darknessinme]

Please someone reply! This is the third time I post these doubts

12. Going down periodic table, electronegativity decreases. Going right, electronegativity increases. So go right from Be, it increases, and go down one it decreases. These cancel so it's electronegativity is similar to Al.
Answer B

13. Did you consider the cis and trans isomers?

29. Two -OH group's add at the double bond with cold,dilute KMnO4. The carbon atoms attached to the -OH groups both become chiral, so +2.
With hot, conc. KMnO4, double breaks, and ketone group and carboxylic acid group form. The carbons still not chiral. The -OH group on the very left of the original molecule is oxidised to ketone, so that carbon becomes non-chiral, so -1.
Answer D.

30. B is acid hydrolysis of a nitrile. You would get ethanoic acid. Question says which would not give. A is base hydrolysis of nitrile, where you get the sodium salt sodium ethanoate.
Answer A.