Chemistry: Post your doubts here!

[Harsh Poddar]

Really nice work and very user friendly.

Thanks

 

[AbbbbY]

its copy pasta from ur quote and not to get praises for my self becoz i myself asked u this question so thnq u again for explaining this question for me and many more whoo had a doubt on this u should be happy ur explaination is being passed ahead u did it to help others or u wanted ur name also to be mentioned.....srry next time i wont repeat.....

Lol. Where did I say you did that to get praises etc :fp1:
It's a help thread, and I pity people who answer to get praises, really.

I'm just saying, going thru the post, I was like, woahh. That sounds sooo much like the way I write, bolding out here are there and the general tone. Then I figured they were my own words -.-

 

[AbbbbY]

Thank You but do you know the logic that why cant we make methyl propane coplanar? Question also tells about rotation about C-C bond. Maybe this information might be useful in this question.

Rotation about the C-C bond wants you to apply the fixed pi bond vs free rotation logic. Since there are no pi bonds in the straight alkane chain, it says that one way or the other, you can rotate the carbons to lie in the same plane. In layman terms, with a branched alkane, how on earth can you possibly line up the branched carbon with the carbon it is connected to and in a same plane? Simply by analyzing the 3d structure you can tell that it's not possible. But, ofcourse, there's a scientific explanation behind this too.

Methyl propane cannot be co-planer because the question says so. Simple enough?

If you want the logic behind that, I can go rambling about it for an hour as to why the hybridization in the branched alkane + the bonding leads to the branched carbon on a different plane but it's NOT exam based, it doesn't have ANYTHING to do with the A Level syllabus and will only confuse you with a little over a week to the exams. If you really want to go on with it, let me know and I'll tell you. You've been warned though. If you end up more confused than before, don't blame me

 

[Namehere]

Rotation about the C-C bond wants you to apply the fixed pi bond vs free rotation logic. Since there are no pi bonds in the straight alkane chain, it says that one way or the other, you can rotate the carbons to lie in the same plane. In layman terms, with a branched alkane, how on earth can you possibly line up the branched carbon with the carbon it is connected to and in a same plane? Simply by analyzing the 3d structure you can tell that it's not possible. But, ofcourse, there's a scientific explanation behind this too.

Methyl propane cannot be co-planer because the question says so. Simple enough?

If you want the logic behind that, I can go rambling about it for an hour as to why the hybridization in the branched alkane + the bonding leads to the branched carbon on a different plane but it's NOT exam based, it doesn't have ANYTHING to do with the A Level syllabus and will only confuse you with a little over a week to the exams. If you really want to go on with it, let me know and I'll tell you. You've been warned though. If you end up more confused than before, don't blame me

Tell us, tell us!

 

[GCE As and a level]

hey guys
how are u all ?
i need a help in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_23.pdf
Q1 B.iii) and C) __ Here i got a correct answer but with a different method , so would i take the full mark,and can u plz tell me how to solve it?
Q2 a,i) and b,i) __ explain it plz
Q4 all __explain it plz
Q5 a,i) __ is CH3CH(OH)CH=CH2 same as CH2=CHCH(OH)CH3 ?
Q5 a,iii)__ could u plz draw the structure ??
____________________________________________________________
and in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_23.pdf
Q3 d)
Q 5 d)
____________________________________________________________
and in :
(unsolved questions) and can u check the solved questions to me?
View attachment 40989 View attachment 40990 View attachment 40991 View attachment 40992
____________________________________________________________
I really need your help
still waiting your help
thanks in advance
wish u all good luck

 

[snowbrood]

help people why is OH- first order?

 

[hope4thebest]

Rotation about the C-C bond wants you to apply the fixed pi bond vs free rotation logic. Since there are no pi bonds in the straight alkane chain, it says that one way or the other, you can rotate the carbons to lie in the same plane. In layman terms, with a branched alkane, how on earth can you possibly line up the branched carbon with the carbon it is connected to and in a same plane? Simply by analyzing the 3d structure you can tell that it's not possible. But, ofcourse, there's a scientific explanation behind this too.

Methyl propane cannot be co-planer because the question says so. Simple enough?

If you want the logic behind that, I can go rambling about it for an hour as to why the hybridization in the branched alkane + the bonding leads to the branched carbon on a different plane but it's NOT exam based, it doesn't have ANYTHING to do with the A Level syllabus and will only confuse you with a little over a week to the exams. If you really want to go on with it, let me know and I'll tell you. You've been warned though. If you end up more confused than before, don't blame me

haha thanks man

 

[thats_me]

View attachment 41071 help people why is OH- first order?

For first order when the conc is doubled the rate is also doubled

Take experiment#2&3
Here the concentration of NaOH is doubled(from 0.1 to 0.2)but rate is not doubled this is due to the decrease in conc of phenacyl chloride(from 0.03 to 0.025)
The rate in experiment#3 should be 3 but instead it's a little less I.e 2.5

The same way if you take experiment#1&3
The rate is more than double again this is due to increase in conc of phencyl chloride

 

[GCE As and a level]

hey guys
how are u all ?
i need a help in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_23.pdf
Q1 B.iii) and C) __ Here i got a correct answer but with a different method , so would i take the full mark,and can u plz tell me how to solve it?
Q2 a,i) and b,i) __ explain it plz
Q4 all __explain it plz
Q5 a,i) __ is CH3CH(OH)CH=CH2 same as CH2=CHCH(OH)CH3 ?
Q5 a,iii)__ could u plz draw the structure ??
____________________________________________________________
and in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_23.pdf
Q3 d)
Q 5 d)
____________________________________________________________
and in :
(unsolved questions) and can u check the solved questions to me?
View attachment 40989 View attachment 40990 View attachment 40991 View attachment 40992
____________________________________________________________
I really need your help
waiting your help
thanks in advance
wish u all good luck

 

[sadiaali]

Please anyone help
In question 3 of M/J 07 chemistry practical ( here is link http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s07_qp_32.pdf ). It state that "Because the solution are coloured you will need to remove traces of solution from precipitates"
So my question is that how we can remove the traces of precipitates. I had done the whole practical in the lab but when i came home and read that. Anyone who had done or had idea about that please share. Thanks

 

[Namehere]

Please anyone help
In question 3 of M/J 07 chemistry practical ( here is link http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_32.pdf ). It state that "Because the solution are coloured you will need to remove traces of solution from precipitates"
So my question is that how we can remove the traces of precipitates. I had done the whole practical in the lab but when i came home and read that. Anyone who had done or had idea about that please share. Thanks

I´m not sure if I understand the question but... Filtre it maybe? Using filter paper or something.

 

[GCE As and a level]

hey guys
how are u all ?
solve as much as u can, even if only one question !!
i need a help in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_23.pdf
Q1 B.iii) and C) __ Here i got a correct answer but with a different method , so would i take the full mark,and can u plz tell me how to solve it?
Q2 a,i) and b,i) __ explain it plz
Q4 all __explain it plz
Q5 a,i) __ is CH3CH(OH)CH=CH2 same as CH2=CHCH(OH)CH3 ?
Q5 a,iii)__ could u plz draw the structure ??
____________________________________________________________
and in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_23.pdf
Q3 d)
Q 5 d)
____________________________________________________________
and in :
(unsolved questions) and can u check the solved questions to me?
View attachment 40989 View attachment 40990 View attachment 40991 View attachment 40992
____________________________________________________________
I really need your help
waiting your help
thanks in advance
wish u all good luck

 

[AbbbbY]

hey guys
how are u all ?
solve as much as u can, even if only one question !!
i need a help in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_23.pdf
Q1 B.iii) and C) __ Here i got a correct answer but with a different method , so would i take the full mark,and can u plz tell me how to solve it?
Q2 a,i) and b,i) __ explain it plz
Q4 all __explain it plz
Q5 a,i) __ is CH3CH(OH)CH=CH2 same as CH2=CHCH(OH)CH3 ?
Q5 a,iii)__ could u plz draw the structure ??
____________________________________________________________
and in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_23.pdf
Q3 d)
Q 5 d)
____________________________________________________________
and in :
(unsolved questions) and can u check the solved questions to me?
View attachment 40989 View attachment 40990 View attachment 40991 View attachment 40992
____________________________________________________________
I really need your help
waiting your help
thanks in advance
wish u all good luck

i - C8H18 + 12.5 O2 -> 8CO2 + 9H2O (Be warned, decimals are not acceptable in equations in exams. either fractions, or whole numbers)

ii - 24.6 mol. (I've cut out the working to keep it short)

iii-
Look. You need the mass of CO2. Instead of finding moles of CO2 from that ratio, just work with masses. Keep it simple and short for yourself.

C8H18 : CO2
144 : 352
24.6*144 : x

x = 24.6 * 352 = 8659.2 = 8660g.

There are several other methods too, but I find this the easiest + shortest. Let me know if this sounds like complete gibberish to you.

C:

My answer to a(iii) is 1.2 x 10^7 tonnes.

100 km = 8660/(1000*1000) tonnes
x km = 1.2 x 10^7

x= 1.39 x 10^11 km

2ai) HCl gas so misty white fumes.
bi) Purple vapor. (The vapor is I2. The HI is oxidised as conc. H2SO4 is a strong oxidising agent. Recap: Group 7.


Q4
a i)
A: No Reaction
NaBH4 reacts with aldehydes to give you primary alcohols and ketones to give you secondary alcohols. This is an alcohol itself so no reaction.

B: No Reaction. Tollens reagent reacts with Aldehydes. This is a Ketone.

C: Ester + Base -> Alcohol + Salt, I guess. CH3COO-+K + (CH3)2CH(OH)

D: No Reaction. (Tertiary Alcohol)

E: CH3CH(OH)CH3

F: (CH3)3CCl

G: HOOCCOOH + CH3COOH

ii
Reaction G goes from Purple to Colorless.
There are other coloured tests too but none of them undergo a colour change as far as I can see.

5 a i) It is.

a iii) Had to do the first part by writing to get to this. I'll send you the whole thing that I did.

NOTE: I didn't have access to any of the marking schemes so please see and let me know if anything up there is incorrect.

3d:
i: Hydrogen bonding!
ii: It's really easy. All you need to do is draw two ethanol molecules and show hydrogen bonding between the Oxygen lone pair + H of the other molecule. Let me know if this doesn't make sense to you and I'll draw them out on a paper.

5d:
5aii tells us that F has a carboxylic group. This takes up 2 of the oxygens. One is left. So either it's a carbonyl or an alcohol. Make it up and all you can have is an alcohol.

Two isomers are possible.

CH3CH(OH)COOH
and
CH2(OH)CH2COOH.

And I don't get what you're asking at the very end + I can't open the attachments

 

[Suchal Riaz]

ZaqZainab
sister can you tell me that does NaBH4 reduces CHO group?

 

[mehria]

ZaqZainab
sister can you tell me that does NaBH4 reduces CHO group?

it reduces aldehyde into primary alcohol n ketone into secondary alcohol

 

[robinhoodmustafa]

ZaqZainab
sister can you tell me that does NaBH4 reduces CHO group?

Aldehyde to primary Alcohol
Ketones to Secondary alcohol

 

[Suchal Riaz]

it reduces aldehyde into primary alcohol n ketone into secondary alcohol

Aldehyde to primary Alcohol
Ketones to Secondary alcohol

sorry i meant does H2 and Ni catalyst reduce CHO?

 

[Suchal Riaz]

sorry i meant does H2 and Ni catalyst reduce CHO?

CH3CH=CHCHO
140 degree + Ni + H2
what will be result?
CH3CH2CH2CHO or CH3CH2CH2CH2OH

 

[kitkat <3 :P]

sorry i meant does H2 and Ni catalyst reduce CHO?

Aren't these the conditions for hydrogenation :/

 

[MiniSacBall]

sorry i meant does H2 and Ni catalyst reduce CHO?

Yes, both NaBH4 and H2 with nickel as catalyst.
H2 with nickel is a pretty powerful reducing agent or (H+)
They reduce almost all of the substances.