Chemistry: Post your doubts here!

[Amy Bloom]

What is the product when (CH3)3CCH2OH is reduced by conc. sulphuric acid?

Normally the alcohol cannot be reduced into an alkane in one step because the -OH bond is reinforced by the 3 electron repelling methyl groups, so not easily removed.
So, no reaction.

 

[Amy Bloom]

http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s11_qp_11.pdf
MCQ 2
how is it A. Shoudnt it b D?

Let the oxidation number of N be x
For:
NO3- .............A............... NO2- .............B...........NO .............C...............N2O................D........ N2
x - 6 = -1 ......................... x - 4 = -1 ..................... x - 2 = 0 .................... 2x - 2 = 0 .................... 0
x = +5 ................................ x = +3 ........................ x = +2 ........................ x = 1 ...........................0
|___ Change = 2________| |__change =1____| |___change=1___| |___change=1___|

Since a change is seen only in A, the answer is A. The change in D is 1, so is in B and C. Hence D is wrong.

P.S Sorry I had to put dots coz when i post, the writings compact & mix up. Hope you'll understand. If you're confused, i'll post it as an image. ok?

 

[Amy Bloom]

Q19?
http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_w07_qp_1.pdf

Well i've tried to find optical isomers for each one of them, see attached file. Well i couldn't find an isomer for the (IV) one.
I think option B is correct.

 

[Amy Bloom]

Can anyone answer this for me:
1. Suggest why the relative atomic mass of Martian oxygen is different from that of oxygen obtained from Earth?
is that because of isotopes of oxygen???

2. The first ionisation energy of oxygen is 1310 Kjmol-1.
Suggest why there is little difference between the first ionisation energies of 16O, 17O and 18O?

 

[larina]

october/november 2011 paper 41
question 2, how do we find the order of reaction for [H+] ??

 

[TheDealer]

Well i've tried to find optical isomers for each one of them, see attached file. Well i couldn't find an isomer for the (IV) one.
I think option B is correct.

Oh yeah!! I totally forgot about the chiral centre part! *facepalm*
Thanks a lot for clearing that out for me Amy!

 

[Ashique]

Hey guys, I have a chemistry practical mock exam tomorrow. Any books, any files, any notes will be so much helpful right now. Any of you have any useful links?

 

[Dayyanah]

Try studyguide.pk its got alot of helpful stuff

 

[Ashique]

Thanks dude. Will look into it now.

 

[Dayyanah]

I kinda need help with chem
oct nov 2011 p53
Qn 1 e)
The ms says 5 marks for; names of gas, Mr, time of effusion, rate of effusion and the units of everything.. im sorta confused, wats the unit of rate of effusion? Grams per mol per second?

And oct nov 2011 p52
Qn 2a)
its says to calculate log (rate of reaction). How is that calculated, is it log (1/time)? Or are there other calculations to do? And how do u obtain a negative ans bcz thts was the ms requires

 

[melly713]

plz explain:
the difference between Sn1 and Sn2 reactions?
an intermediate in a reaction ?
in brief detail plz with examples thanku

 

[samwickz]

Which element has an equal number of electron pairs and of unpaired electrons within orbitals of
principal quantum number 2?
A beryllium
B carbon
C nitrogen
D oxygen

how to work it out? kinda stuck + i suck @ chem

 

[CaptainDanger]

plz explain:
the difference between Sn1 and Sn2 reactions?
an intermediate in a reaction ?
in brief detail plz with examples thanku

Read this : http://www.chemguide.co.uk/mechanisms/nucsub/whatis.html

 

[smzimran]

Which element has an equal number of electron pairs and of unpaired electrons within orbitals of
principal quantum number 2?
A beryllium
B carbon
C nitrogen
D oxygen

how to work it out? kinda stuck + i suck @ chem

Electronic configurations:
Be = 1s2 2s2
C = 1s2 2s2 2p2
N = 1s2 2s2 2p3
O = 1s2 2s2 2p4

In the second shell, the two orbitals are 2s2 and 2p6; the carbon atom is the only one having equal number of electrons in both....
So, the answer is B...

 

[smzimran]

I kinda need help with chem
oct nov 2011 p53
Qn 1 e)
The ms says 5 marks for; names of gas, Mr, time of effusion, rate of effusion and the units of everything.. im sorta confused, wats the unit of rate of effusion? Grams per mol per second?

And oct nov 2011 p52
Qn 2a)
its says to calculate log (rate of reaction). How is that calculated, is it log (1/time)? Or are there other calculations to do? And how do u obtain a negative ans bcz thts was the ms requires

It would be helpful if you attach the link to the papers...

 

[Amy Bloom]

Can anybody check that, i can't find the correct value for the rate constant.

 

[smzimran]

october/november 2011 paper 41
question 2, how do we find the order of reaction for [H+] ??

Compare with 1
[CH3CHO] remains same
[CH3OH] increases 1.6 times and we know its order of reaction is 1 so the rate increases by 1.00 * 1.60 = 1.60
[H+] increases 2 times and checking the rate, it also increases by 2 times (1.60 * 2 = 3.20)

Therefore, order of reaction is 1 for [H*]

 

[smzimran]

Can anybody check that, i can't find the correct value for the rate constant.

Your order of reaction for [NO] is wrong, it is not 0, it is 2
Check experiments 1 and 2:
[H+] is constant so lets check [NO]
[NO] increases 2 times and the rate increases (0.013/0.0033) = 4 times which is 2^2 times
Therefore order of reation w.r.t [NO] is 2
Iam sure you can solve rest of the parts easily...

 

[smzimran]

Can anyone answer this for me:
1. Suggest why the relative atomic mass of Martian oxygen is different from that of oxygen obtained from Earth?
is that because of isotopes of oxygen???

2. The first ionisation energy of oxygen is 1310 Kjmol-1.
Suggest why there is little difference between the first ionisation energies of 16O, 17O and 18O?

1. YOu are right that is because of isotopes..
2. I dont get your question

 

[Dayyanah]

http://www.mediafire.com/?dgcbc88stxh5f#ky26680wf3ich
I dont know if it will work.. the papers arent there on the papers area...

P52 and 53