Chemistry: Post your doubts here!

[saudha]

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

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]

AoA,

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

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:

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

 

[Hussnain]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_er.pdf
Paper 5
Q1 (e)
Q2. What is the mass of water in the saturated solution? How will we came to know about this?

Please reply ASAP.

 

[smzimran]

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.

 

[rehan751]

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

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.

 

[nonamehapazard]

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

 

[geek101]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s04_qp_1.pdf can someone please explain Q9. the answer is B

thank you

 

[étudiante]

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

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

 

[Chooi1993]

Anyone know how to do question 7 (a) ? How to draw the diagram ?
http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_w09_qp_42.pdf

 

[Scafalon40]

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

 

[srijitsharma]

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!

 

[smzimran]

Guys any guessing whats coming in the chemistry AS practical variant 33. That is taking place on may 10th. Plz help

No discussion about that here or this thread also gets locked by the mods!!!

 

[Scafalon40]

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).

Look at the equation even more closely, option A is that HSO3^- is acting as a base.

 

[Scafalon40]

No discussion about that here or this thread also gets locked by the mods!!!

Or removed because the mods can't take a joke...

 

[Chooi1993]

Anyone know how to do question 7 (a) ? How to draw the diagram ?
http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_w09_qp_42.pdf

 

[iKhaled]

need explanations to some questions in paper 1 nov/oct 10..
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_11.pdf

Q7....why is it C and not D
Q10

 

[Scafalon40]

need explanations to some questions in paper 1 nov/oct 10..
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf

Q7....why is it C and not D
Q10

Angle 1)109.5
Angle 2)120
Angle 3)104.5
For Q10
It forms a quadratic equation
The answers are 4 and 2/3

 

[iKhaled]

Angle 1)109.5
Angle 2)120
Angle 3)104.5
For Q10
It forms a quadratic equation
The answers are 4 and 2/3

for question 10 ik that it has something to do with algebra but can u please show me the work out if u dont mind bro..?

 

[Scafalon40]

for question 10 ik that it has something to do with algebra but can u please show me the work out if u dont mind bro..?

You'll have to wait a little: busy but i'll post in a few minutes

 

[Scafalon40]

lets do this, i'll need your input too because you'll learn it better...
What are the initial moles?
1,1,0,0 ( form the equation for the reaction)
what are the equilibrium moles?
1-x,1-x,x,x
What is the expression for the Kc?
What is the value of Kc?
Ring a bell?