Chemistry: Post your doubts here!

[strangerss]

answer is B
amount of sulphite use = conc x vol
= 0.1 x (25/1000)
=2.5x10^-3mol
2 electrons are lost
amount of electrons lost = 2 x 2.5 x 10^-3 ==== 5 x 10^-3 mol
amount of electorns gained by metallic salt = amount of electrons lost by sulphite
= 5 x 10^-3 mol
amount of metallic salt used = 0.1 x (50/1000) ==== 5 x10^-3
amount of electrons gained PER MOLE of salt = (5 x 10^-3)/(5x10^-3) = 1 unit
hence oxidation state of metallic salt decreases by 1 unit meaning the oxidation satate becomes +2 from +3!!!

thanks a lot

 

[darkxangel]

Can someone please help me with this question ?

 

[strangerss]

Noo Q19 (B) and Q28 (A) according to the mark scheme

Okay I rechecked and in Q19 the optical isomer of iii is C*H(I)CH3CH2I the Carbon with the asterisk is the chiral center and u figured out i and ii right? in Q 28 I messed up the double IS broken in A with the addition of hydrogen , but I didn't know that an adldehyde is also oxidised to a primary alcohol by hydrgenation I never studied that :/ and in C it's wrong because the double bond id broken by nabh4 which is wrong because it will only reduce the aldehyde to a primary alcohol.. Hope you got it now and sorry for the wrong answers :/

 

[cute97]

GUYZZZ CHECK THIS REPEATED QUESTION THE MARK SCHEME GAVE TWO DIFFRENT ANSWERS !!! HELP
Q12http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
and this is the mark scheme for JUNE 06
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_ms_1.pdf
Q11http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf
and this is the mark scheme for NOVEMBER 11
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_11.pdf
what is the correct answer ????

 

[Aries_95]

GUYZZZ CHECK THIS REPEATED QUESTION THE MARK SCHEME GAVE TWO DIFFRENT ANSWERS !!! HELP
Q12http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
and this is the mark scheme for JUNE 06
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_ms_1.pdf
Q11http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf
and this is the mark scheme for NOVEMBER 11
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_11.pdf
what is the correct answer ????

The answers are correct.
Look again at the options, they are shuffled. the option C in s_O6 is option A in w_11 hence the answers are C and A respectively.

 

[Dr.MMM]

C10H14O must be an ALCOHOL because an ALKENE is formed when this compound is dehydrated! and it must b a TERTIARY ALCOHOL, as only tertiary alcohols are not readily oxidised!!!!!
looking at the options:
A,B and C are secondary alcohols! as none of the carbon on which the double bond is fromed has an alkyl group!! a TERTIARY GROUP has an alkyl group left after the formation of a double bond! hence D is correct!

Thanks

 

[Dr.MMM]

Oh and ive got another question:
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s05_qp_1.pdf Q:40th

 

[daredevil]

GUYZZZ CHECK THIS REPEATED QUESTION THE MARK SCHEME GAVE TWO DIFFRENT ANSWERS !!! HELP
Q12http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
and this is the mark scheme for JUNE 06
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_ms_1.pdf
Q11http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf
and this is the mark scheme for NOVEMBER 11
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_11.pdf
what is the correct answer ????

yaar the options in both the papers are different. option C from Q12 is same as option A from Q11. these are the SAME and CORRECT answers.

 

[cute97]

yaar the options in both the papers are different. option C from Q12 is same as option A from Q11. these are the SAME and CORRECT answers.

hahahhahahhhaa its seems i must take a break now

 

[daredevil]

hahahhahahhhaa its seems i must take a break now

hahha.... that;s always a gud option

 

[darkxangel]

Can someone please help me with this question?
Nov2011 qp 12

 

[daredevil]

Two equilibria are shown below.
reaction I 2X2(g) + Y2(g--> 2X2Y(g)
reaction II X2Y(g)---> X2(g) + 1/2Y2(g)

The numerical value of Kc for reaction I is 2.
Under the same conditions, what is the numerical value of Kc for reaction II
ans is 1 / root 2 ??

subsitute the equation for kc of the first reaction into the kc of the second reaction. product changes into reactant so the Kc (2) will be reciprocalled too and become 1/2.
then in the first equation there were 2 mol of X2Y so it was squared in the equation. in the second reaction is is just one so does not need to be squared so square root is taken on both sides of the eq.
if u don't get it like this then tell me and i'll see if i can write out the eq. here.

 

[daredevil]

Can someone please help me with this question?
Nov2011 qp 12

umm i think an aldehyde will be formed bcz it is distilled (and not refluxed) so write out an eqation for the formation of an aldehyde from this alcohol.
calculate the moles of ethanol according to the mass given and then use mole ratio (as in the equation) to find moles of aldehyde. use moles and Mr of aldehyde to find mass. use the percentage yield formula and incorporate the theoretical yield and the percentage yield in it to find the practical - or actual - yield of the product i.e. aldehyde.
if u cant solve it then tell me and i'll do it. i don't have a pen and paper handy ryt now

 

[ahmed abdulla]

can u write it in the format : (for second question)
intial:
difference:
at equilibrim : >?
for first question no idea at all (ATTACHED)

 

[shaikh]

The equation below represents the combination of gaseous atoms of non-metal X and of
hydrogen to form gaseous X2
H6 molecules.
2X(g) + 6H(g) → X2
H6(g) ∆H = –2775kJmol–1
The bond energy of an X–H bond is 395kJmol–1
.
What is the bond energy of an X–X bond?
A –405.0kJmol–1
B –202.5kJmol–1
C +202.5kJmol–1
D +405.0kJmol–1


Can someone plz answer this ?

 

[Rahma Abdelrahman]

Nov 09 P12, can someone explain Q 18 , Q20 , Q22_Why not B? And Q40 ...
And in June 2010 P11 Q35?!!! How is it C?!! How is Carbon wrong while Sulfur is right?!!! I really don't get it!
Please reply asap ...

 

[soso247]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_11.pdf
please help
question 21, 23, 28, 29, 31

 

[soso247]

I guess someone already helped... may be another time

here is another one can you help me with it please

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_11.pdf
please help
question 21, 23, 28, 29, 31

 

[Fma 07]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_11.pdf

Q6. Answer is D
Q9. Answer is C (im getting 2.952 grams)
Q11. Answer is A
Q20. Answer is C
Q21. Answer is C (im getting 5? )
Q22 Answer is B
Q28 Answer is D
Q29 Answer is B
Q30 Answer is D ( which one is the chiral centre? )
Q32 Answer is D which one is reduction?
Q35 Answer is C.

( I realise theyre alot of questions..sorryy )

 

[soso247]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_11.pdf

Q6. Answer is D
Q9. Answer is C (im getting 2.952 grams)
Q11. Answer is A
Q20. Answer is C
Q21. Answer is C (im getting 5? )
Q22 Answer is B
Q28 Answer is D
Q29 Answer is B
Q30 Answer is D ( which one is the chiral centre? )
Q32 Answer is D which one is reduction?
Q35 Answer is C.

( I realise theyre alot of questions..sorryy )

hey
so Question 6
NH4NO3→ N2O + 2H2O
treat NH4+ and NO3- as separate and get the oxidation state on each ..... N in NH4+ has the oxidation state of -3 and in NO3- it has an oxidation state of +5 and since in N2O the oxidation state is 1 you get from -3 to 1 which is +4 and from +5 to +1 is -4

question 9
i am getting 2.995 and hence it is the only one closest to 3 so it is right and so it is C

question 11
when you add acid the H+ react with OH- to form water and hence the equilibrium of the equation shift to the right to create more HOCl and so reducing OCl- and hence it cannot for cl- under uv light

question 20
anything flammable burns in oxygen and because oxygen cannot burn in oxygen (obviously) then oxygen is non-flammable

question 21
i will post a picture for explanation later

question 22
later

question 28
only tertiary halogenoalkane are unaffected by the concentration of OH- and D is the only tertiary halogenoalkane

Q29
but-1-ene, cis-but-2-ene, trans-but-2-ene are all isomers of butene formed from but-2-ol

Q30
the 3rd Carbon is the chiral centre