Chemistry: Post your doubts here!

[Suchal Riaz]

wats expansion of octate rule ._. :'(

octet rule is wrong any ways so forget about it's expansion.
electron get attracted by all positive charged nucleus. and where there is larger attraction they move towards there. the electrons in between two nuetrons keep then together. and electrons will bond as long as it is energetically feasible and there is space to bond. octet rule works most of the time because we ignore transition metals and 4s is lower than 3p in energy level.

 

[Suchal Riaz]

Ohh thanks how stupid was that ! :/ .. .anyways Is it okay to draw the displayed formulae instead of the structure formulae in the exam ? or we should stick to structural formula as asked ? and will they reduce marks or what ?!

it is NOT okay to draw display instead of structural. it will show that u can't manage to squeeze the information into small space.

 

[Suchal Riaz]

it's ok...calm down brother

no its not okay
feeding wrong information to kids. babysitting small kids! duh. lower the marks for A so more people can get A. and the syllabus is so small that A should be on 99%.

 

[mehria]

no its not okay
feeding wrong information to kids. babysitting small kids! duh. lower the marks for A so more people can get A. and the syllabus is so small that A should be on 99%.

hmmm.... :/ but still most of the ppl find the syllabus difficult....

 

[Namehere]

no its not okay
feeding wrong information to kids. babysitting small kids! duh. lower the marks for A so more people can get A. and the syllabus is so small that A should be on 99%.

You must have a good teacher, because other people have **** "teachers" and therefore struggle to achieve the grades they are "supposed" to have. As always, being alone is better that being with someone who influences you badly.

And i disagree with your argument that an A should be on 99% ^^, since it would mean you are at an immense disadvantage on other people doing different, easier, examination boards.

 

[Haya Ahmed]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_21.pdf

Q3
i
ii
iv
v

 

[zackle09]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
can someone PLEASEEEE explain question 5b(iv)?!

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_21.pdf

Q3
i
ii
iv
v

the answers are available in markscheme. do u want explanation?

 

[Haya Ahmed]

the answers are available in markscheme. do u want explanation?

LOL of course .. I'm not that lazy to check ms !

 

[Suchal Riaz]

LOL of course .. I'm not that lazy to check ms !

first group metals have less density. so they ill float on water.
carbon monoxide is a reducing agent(we learned that in iron manufacturing in o level)
K has smallest ionisation energy becuase it is the biggest atom.
Carbon has a giant molecular structure(graphite, diamond) but CO2 is not giant. sillicon is also giant but SO2 is also giant so it is wrong.
Cl has smallest anion as all anions in period 3 have same number of electrons in outer shell. but chlorine has highest +ve charge. so it's electron will be attracted most strongly.
AlCL3 has low melting point. it vaporises on bunsen burner temperatures. but Al2O3 has much higher melting point.

 

[Haya Ahmed]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_21.pdf

Q5 (a) ... (C) part .. why the aldehyde is converted to CH2OH .. and Is that because we added Hydrogen so Hydrogenation process happened ?!

 

[Exo_luhan]

While we draw chiral compounds is there any specific rule as to which (CH3/OH/COOH etc) will be coming out of page and to which will be going into page?

 

[Exo_luhan]

Which all mechanisms do we need to know for P2?

 

[robinhoodmustafa]

No.

part ii is reaction with 2,4 DNPH.. which tells us if there is a carbonyl group present or not.

Carbonyl = Ketone AND Aldehyde both not just ketone..

I mean since you have already told in part i, that it's not a aldehyde the examiner might give you marks for it's not a ketone. But I wouldn't risk it.

The correct Answer for this will be. "The compound doesn't have a carbonyl group" or "No Ketone or Aldehyde present in compound R".

Can we just wri

i am talking after reading research papers from top universities including university of new york.
and that can NOT be wrong. I have even seen come textbook used in BS in chemistry in cambridge university containing things that are against our A level syllabus.
they know everything but they have simplified the things to the point of being wrong. and i can handle a syllabus 10X the current size. and i hate to learn wrong things.

Alevels chem is full of contradictions. Like they invented Ideal gas law but does any one of a gas exist which follow its condition?
we were told to ignore it as british are too much sensitive in this matter.

 

[Browny]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_qp_2.pdf

Can anyone explain why in Q3)b)ii) why they are saying in the marking scheme that bonding changes from covalent to ionic?
Because my opinion is that HCl is ionic.

 

[BeBeskii108]

I've done more than 10 Paper4's and I still get around 50-60. Any suggestions ? Those papers seem to vary from each other a lot. Very few straightforward answers. Can somebody please give a link of organic chemistry reactions required for A2 ?

 

[AbbbbY]

While we draw chiral compounds is there any specific rule as to which (CH3/OH/COOH etc) will be coming out of page and to which will be going into page?

It's a 3D structure so really, it makes no difference.

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_2.pdf

Can anyone explain why in Q3)b)ii) why they are saying in the marking scheme that bonding changes from covalent to ionic?
Because my opinion is that HCl is ionic.

HCl IONIC!???! Good Lord!

2 days to p2 mate! HCl isn't ionic, it's covalent. Cl has 7 outer electrons, H has a single electron. How can they ever be ionic.

It shows ionic character in water because it's polar-covalent. HCl + H2O -> H3O+ + Cl- [thus an acid.]

 

[robinhoodmustafa]

HCl IONIC!???! Good Lord!

2 days to p2 mate! HCl isn't ionic, it's covalent. Cl has 7 outer electrons, H has a single electron. How can they ever be ionic.

It shows ionic character in water because it's polar-covalent. HCl + H2O -> H3O+ + Cl- [thus an acid.]

If its ionic in water than it must show a base nature so why have to called the product an acid?

 

[AbbbbY]

If its ionic in water than it must show a base nature so why have to called the product an acid?

What?