Author Topic: ALL CIE CHEMISTRY DOUBTS HERE !!  (Read 122965 times)

Offline Deadly_king

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #315 on: December 09, 2010, 08:09:48 am »
http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w04_qp_1.pdf

Question 13. I understand the answer is D and that you need a strong acid and base, but why ? What is the chemistry behind all of this ?

Why wouldnt a strong acid and weak base give a SHARP colour change ?

What chapter does this appear in the chem book by Brian Ratcliff ?

A strong acid and a strong alkali gives the sharpest end-points. Weak bases or acids take more time to dissociate and hence the end-point is not as sharp as that using strong solutions.

It appears in the chapter Equilibria ---> The part in A2 where you deal with indicators.

elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #316 on: December 10, 2010, 01:00:41 pm »
http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w05_qp_1.pdf

Question 3

I know the answer is B... I actually got this question correct. However, I want to check if my reasoning is correct and that I didnt get this by some fluke.

Once the p electron in option B is removed a fully filled s orbital is left. This orbital has a stable arrangement of electrons because it is filled and hence requires a larger IE to remove these electrons.

Is this correct ?

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #317 on: December 10, 2010, 01:11:29 pm »
http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w05_qp_1.pdf

Question 3

I know the answer is B... I actually got this question correct. However, I want to check if my reasoning is correct and that I didnt get this by some fluke.

Once the p electron in option B is removed a fully filled s orbital is left. This orbital has a stable arrangement of electrons because it is filled and hence requires a larger IE to remove these electrons.

Is this correct ?

Yes , I chose B too because the Element is in Group 1 , ur explanation ,hence the Highest I.E. among the other =]
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Offline Master_Key

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #318 on: December 10, 2010, 01:29:39 pm »
Yes , I chose B too because the Element is in Group 1 , ur explanation ,hence the Highest I.E. among the other =]

To remove the first electron is easy as it is the only electron, but next shell is full, sheilding effect is higher and thus requires higher energy.

elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #319 on: December 21, 2010, 08:07:15 am »
When the yellow liquid NCl3 is stirred into aqueous sodium hydroxide, the reaction that occurs
can be represented by the following equation.

2NCl3(l) + 6NaOH(aq) ---> N2(g) + 3NaCl (aq) + 3NaOCl (aq) + 3H2O(l)

What will be the result of this reaction?

1 The nitrogen is oxidised.
2 A bleaching solution remains after the reaction.
3 The final solution gives a precipitate with acidified silver nitrate.

The MS says 2 and 3 are correct only.

Why isnt 1 also correct ? It is obvious that Nitrogen goes from an oxidation state of -3 in NCl3 to 0 in N2. Hasnt the Nitrogen been oxidised?

Offline Deadly_king

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #320 on: December 21, 2010, 11:15:16 am »
When the yellow liquid NCl3 is stirred into aqueous sodium hydroxide, the reaction that occurs
can be represented by the following equation.

2NCl3(l) + 6NaOH(aq) ---> N2(g) + 3NaCl (aq) + 3NaOCl (aq) + 3H2O(l)

What will be the result of this reaction?

1 The nitrogen is oxidised.
2 A bleaching solution remains after the reaction.
3 The final solution gives a precipitate with acidified silver nitrate.

The MS says 2 and 3 are correct only.

Why isnt 1 also correct ? It is obvious that Nitrogen goes from an oxidation state of -3 in NCl3 to 0 in N2. Hasnt the Nitrogen been oxidised?

Dude the oxidation number of nitrogen in NCl3 is +3 and not -3. Therefore it gets converted to 0 which means it is reduced. ;)

elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #321 on: December 21, 2010, 11:15:45 am »
http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s10_qp_11.pdf

I must be really daft.... but I cant figure out why the answer is as stated in the MS.

Question 1
« Last Edit: December 21, 2010, 11:28:18 am by Ari Ben Canaan »

elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #322 on: December 21, 2010, 11:18:24 am »
Dude the oxidation number of nitrogen in NCl3 is +3 and not -3. Therefore it gets converted to 0 which means it is reduced. ;)

Damn, right. Can you answer my other question ?

Offline Deadly_king

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #323 on: December 21, 2010, 11:55:00 am »
http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s10_qp_11.pdf

I must be really daft.... but I cant figure out why the answer is as stated in the MS.

Question 1

1.What could be the proton number of an element that has three unpaired electrons in each of its
atoms?
A 5
B 13
C 15
D 21

You just have to write the electronic configuration of the elements.
5 -----> 1s22s22p1 : Only one unpaired electron.

13 -----> 1s22s22p63s23p1 : Only one unpaired electron at all.

15 ------> 1s22s22p63s23p3 : 3 unpaired electrons only.

21 ------> 1s22s22p63s23p64s23d1 : Only one unpaired electrons.

So answer is C. ;)

Is it right?

elemis

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #324 on: December 21, 2010, 12:03:02 pm »
I got answer C too.... I think I was looking at the wrong MS at the time -_-

Offline Deadly_king

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #325 on: December 21, 2010, 12:05:58 pm »
I got answer C too.... I think I was looking at the wrong MS at the time -_-

Hehe.........no worries br0. :)

Just be a bit more careful next time. :D

Offline Sue T

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #326 on: December 28, 2010, 04:31:27 pm »
A2 question:
does it matter wether th reagent used for the hydrolysis of an amide is said as :
(A) aq acid/alkali and reflux
or
(B) H3O+ or  H+  or  OH-?
does it differ if we're talkin bout a protein or normal amide -- cuz in th past pprs sometimes it says smthin n others ts smthin else. i ignored it at first but its gettin on my nerves now...
ny ideas?
n also they cnt decide wether they want us 2 say reflux or simply heat  >:(
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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #327 on: December 31, 2010, 08:39:21 pm »
A2 question:
does it matter wether th reagent used for the hydrolysis of an amide is said as :
(A) aq acid/alkali and reflux
or
(B) H3O+ or  H+  or  OH-?


No, it doesnt matters. They act. mean the same thing. ::)
Although, an equation for this reaction is simply written as (for eg:-)

Ch3CONHCH3 +H2O +H+(aq)----------> CH3COOH + CH3NH2

Quote
does it differ if we're talkin bout a protein or normal amide -- cuz in th past pprs sometimes it says smthin n others ts smthin else. i ignored it at first but its gettin on my nerves now...
ny ideas?

Have a look at this  ;) http://www.chemguide.co.uk/organicprops/aminoacids/proteinhydrolysis.html

Quote
n also they cnt decide wether they want us 2 say reflux or simply heat  >:(

Amides may be hydrolysed by heating under the reflux with either an acid or an alkali. :-X
« Last Edit: December 31, 2010, 08:47:50 pm by Amelia »

Offline Sue T

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #328 on: January 02, 2011, 03:15:09 pm »
thanks amelia!
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Amelia

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Re: ALL CIE CHEMISTRY DOUBTS HERE !!
« Reply #329 on: January 02, 2011, 07:04:24 pm »
thanks amelia!

Glad to be of help, mate. :)