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Chemistry: Post your doubts here!

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geek101

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gary221 said:
So doesnt ths mean tht although a ketone cnt hydrogen bond wth itself, it can wth othrs??
Click to expand...

ill chip in, hydrogen bonds are only formed when H is attached to F, O or N, otherwise if there is a bond with electronegativity difference (usually an atom attached to F, O, N, Cl, or Br) then the intermolecular forces will be permanent dipole-dipole interactions. So in a carbonyl group the bond is a C=O which is polar, thats why within the ketone you will find permanent dipole-dipole interactions and not hydrogen bonding. hope thats right :p
 
saudha

saudha

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melly713 said:
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_11.pdf #30 and # 29..plz explain thank u ;)
Click to expand...


i dint get 29.... but got 30
30 30 Which compound exhibits both cis-trans and optical isomerism?
A CH3CH=CHCH2CH3
B CH3CHBrCH=CH2
C CH3CBr=CBrCH3
D CH3CH2CHBrCH=CHBr

a compound which contains both optical isomer ( a C compound with 4 different group, a chiral centre) and a cis-trans isomerism

a- cannot be optical, as non of the carbon is a chiral centre,whereas it has cis-trans isomerism.
b-does not have cis-trans isomerism
c-has cis-trans but not optical isomerism
d -has both cis - trans and a chiral centre
you have to draw and workout , and you will get the right answer
so d is the answer.
hope you understand, if u dont pls ask the doubt
 
smzimran

smzimran

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AoA,
CaptainDanger said:
Q-40?
9701_s10_qp_11.pdf
9701_s10_ms_11.pdf


Q-40?
9701_s05_qp_1.pdf
9701_s05_ms_1.pdf


Q-38?
Why is B correct?
9701_s06_qp_1.pdf
9701_s06_ms_1.pdf
Click to expand...
june 10/ Q40:
This is reflux heating,
1 and 2 are correct because they are to be heated under reflux!
in 3, the reactant ethene is a gas! So, it cannot be done this way for ethene

june05 /Q40:
lplp.png
2 shows the acid obtained correctly (Na+ is due to the alkaline hydrolysis)
1 shows the correct alcohol
3 is wrong as it shows the breaking of the double bond, which is incorrect.
That is why B is the answer!

june06 / Q38
It is a single reaction they are talking about!
1 and 2 can be easily made in a single reaction
3 cannot, it is the transition state of Sn2
That is why B is correct
 
smzimran

smzimran

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These questions were asked by:
maleeha123

Q5:
See the pattern
There is a comparatively large gap b/w 3rd and 4th ionisation energies
2nd - 1st = 1800 - 950 = 850
3rd - 2nd = 2700 - 1800 = 900

4th - 3rd = 4800 - 2700 = 2100
See the difference
That means change of shell after 3rd electron and 3 electrons in last shell
So the oxidation state is +3
and the formula of the chloride is XCl3
The answer is C

Q32:
1 is false as increase in temperature may speed up or slow down a reaction but not totally stop it!!!
2 is correct using Le Chatilier principle
3 is also correct as seen from the endothermic enthalpy change
So, the answer is C

Q37:
1 is wrong because H. free radical is never produced in that reaction, consult a text book for detail.
2 and 3 are correct
C is the answer.
 
R

rehan751

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melly713 said:
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_11.pdf #30 and # 29..plz explain thank u ;)
Click to expand...

I don't know about 29's reason but I know that Alkene obtained from dehydration of but-2-nol will have 3 isomers so 3 alkenes. So B

For 30, Please view the picture in full size otherwise you'll find it too small:

http://img685.imageshack.us/img685/8421/001jwvf.jpg

Remember there is no need for writing down full structures as you obviously won't have enough time but I did to explain it. Just have a look at only the double bonded carbons for cis-trans isomerism, if they have any 1 similar element or group on both side it shows cis-trans isomerism.

Similarly only look at single-bonded carbon for optical and see if any carbon has 4 different groups or elements surrounding it.
 
N

nonamehapazard

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can any body give me some tricks to solve chemistry p1 questions? you know time always matters.how to tackle mcqs easily?
 
étudiante

étudiante

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geek101 said:
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s04_qp_1.pdf can someone please explain Q9. the answer is B

thank you :)
Click to expand...
HCl is a monobasic acid...
so options of sulphuric acid (its dibasic) and NaOH (alkali) are out...
ethanoic acid is a weak acid so it will not undergo too much dissociation like HCl... thus only nitric acid is possible as it is monobasic and strong and thus the concentration of H+ ions will be roughly same as HCl :)
urw :)
 
Scafalon40

Scafalon40

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Can anybody answer the question in my signature?
Scroll down, it'll be in coloured fonts...
 
srijitsharma

srijitsharma

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In chemistry p1, I heard there is a secrect way of solvin g the numerical problems without calculations, can anyone please tell me how can it be done!
 
Scafalon40

Scafalon40

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Jaf said:
It's A.
Look at this equation closely:
HSO3 (–) + H (+) <------> SO3 (2–) + 2H (+)
The resulting solution in the forward reaction has one more proton. Hence, HSO3 (-) is acting like a proton donor (Bronsted-Lowry Acid).
Click to expand...
Look at the equation even more closely, option A is that HSO3^- is acting as a base.
 
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