ALL CIE CHEMISTRY DOUBTS HERE !!

[Deadly_king]

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]

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 ?

[The Golden Girl =D]

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 =]

[Master_Key]

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]

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?

[Deadly_king]

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]

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

[elemis]

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 ?

[Deadly_king]

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]

I got answer C too.... I think I was looking at the wrong MS at the time -_-

[Deadly_king]

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.

[Sue T]

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 

[Amelia]

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

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

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.

[Sue T]

thanks amelia!

[Amelia]

thanks amelia!

Glad to be of help, mate.