Chemistry's Question.

[Zishi]

Question number 36: http://www.xtremepapers.net/CIE/International A And AS Level/9701 - Chemistry/9701_s08_qp_1.pdf

I can 100% say that Nitrogen IS oxidized in it, but marking scheme says that it isn't. =/

 

[hassam]

ya agree wid u ,....oxygen is oxidised bt dont knw y ms says it is nt

 

[farrukh]

nitrogen is not oxidized it is reduced...oxidation number of nitrogen in NCL3 is +3 and in diatomic nitrogen it is 0...So nitrogen is reduced
Correct optionsare 2 and 3.

 

[UxaiR]

yes !
Remember that Stable diatomic atoms are Always having 0 (zero) oxidation state !
so Nitrogen is reduced !

ya agree wid u ,....oxygen is oxidised bt dont knw y ms says it is nt

it's Nitrogen , Not oxygen

 

[Zishi]

Well, the truth is Nitrogen's Electronegativity is greater than chlorine, so it would get its original oxidation number first, so its oxidation number SHOULD be -3. =/

 

[hassam]

ya zishi is rite.....go and check AS and a level chemistry by radcliffe...its written in electrochemistry chapter that the more electronegative element is given the
-ve oxidation state

 

[farrukh]

how can u be 100% sure that nitrogen has greater electronegitivaty than chlorine...According to textbook both have same value of 3.
so i applied the o level concept of all halogens always having -1 oxidation number

 

[Zishi]

Well, do check it out: http://en.wikipedia.org/wiki/Electronegativity

In the first periodic table they've given that electronegativity of Chlorine IS greater than Nitrogen, but in second periodic table they've shown that Chlorine has less electronegativity than nitrogen.

 

[farrukh]

hmm which one to chose?...lol

 

[hassam]

well for electronegativity chemists hav made a pauling scale according to which nitrogen has the highest en value of 3.98

 

[loly23]

yeah..nitrogen is reduced as its oxidation number decreases from +3 to 0.

 

[Zishi]

Well, I've searched on this a lot. The thing is some scientists say that Nitrogen and chlorine have very very less difference in their electronegativity, so they're considered to have same number 3.0. Whereas the new scales say that chlorine has greater electronegativity, and the old 'Pauling' scale says that nitrogen has greater electronegativity. And what I guess that CIE thinks that chlorine has more elctronegativity, so we'd have to be with new scale. :shock:

 

[kahynickel]

The electronegativity of nitrogen is 3.0 and that of chlorine is 3.25. Always remenber that there are only ATOMS which make chlorine partially positive (or drags its electrons) these are Fluorine(3.98) and Oxygen(3.5)-both are more electronegative than Chlorine.

The june 2008 question was correctly answered by Farrukh he also explained his answer.

Nitrogen has a formal charge of +3 in NCl3 and in the resulting compound N2 it 0. Therefore its oxidation number decreases means it gained electrons- it is redeced. this eleiminates choice 1 and thus 2 and 3 are correct means that C is answer.

Now some examples of Cl in combination with O and F.

NaClO (Na= +1 Cl = +1 O = -2) ClO2 ( Cl = +4 O= -4) for this go june 08/paper 4 Q.2a(iii)
ClF (Cl= +1 F= -1)