STPM化学专区

idontwant2b

可以列列哪几种吗？
本人inorganic原本都不好了，
现在才知道连那些reagent颜色也要背，
2008出了，2009还是可能出。

Dicardo

原帖由 idontwant2b 于 8-11-2009 11:03 PM 发表
请问考试complex的颜色要背吗？
2008的好像要背的耶。

重要的才要被。。。像CuSO4, CuCl4

darksider

原帖由 idontwant2b 于 2009/11/9 01:10 AM 发表
可以列列哪几种吗？
本人inorganic原本都不好了，
现在才知道连那些reagent颜色也要背，
2008出了，2009还是可能出。

Cr(3+)(aq)
Cr(OH)3 (green ppt) ;
add NaOH in excess---> [Cr(OH)6](3-) ... green solution
add NH3 in excess ---> [Cr(NH3)6(3+) ... green solution

Fe(2+)(aq)
Fe(OH)2 dark green ppt ;
add NaOH in excess ---> Fe(OH)3 dark brown ppt (oxidation)
add NH3 in excess --->  Fe(OH)3 dark brown ppt (oxidation)

Fe(3+)(aq)
add NaOH in excess ---　Fe(OH)3 dark brown ppt
add NH3 in excess --->  Fe(OH)3 dark brown ppt

Co(2+)(aq)
Add NaOH in excess ---> Co(OH)2 blue ppt
add NH3 in ecess ----> Co(OH)2 dissolves to form brown solution of [Co(NH3)6](2+)

Ni(2+）
Add NaOH in excess ---> green ppt of Ni(OH)2
Add NH3 in excess ----> green ppt of  Ni(OH)2 dissolves to form pale blue solution Ni(NH3)6](2+)

Cu2+
Add NaOH in excess ---> Blue ppt of Cu(OH)2
Add NH3 in excess ---> blue ppt of Cu(OH)2 dissolves to give deep blue solution of [Cu(NH3)4] (2+)

This also remember (in neutral solution) ; water acts as ligand
Copper
[Cu(H2O)6](2+) + NH3 (in excess) ----> [Cu(NH3)4]2+
pale blue                                                 deep/dark blue

[Cu(EDTA)]2+ --- light blue  ; CuCl4(2-) ---- yellow

Cobalt
[CoCl4]2- + 6H2O ---->  [Co(H2O)6]2+ + 4Cl-
blue                                         pink

[Co(NH3)6]2+ --- yellow ; [Co(H2O)6]3+ --- brown

Iron
*[Fe(H2O)6]2+ --- pale green ; [Fe(H2O)6]3+ --- yellow
[Fe(CN)6]4- & [Fe(CN)6]3- --- yellow
[Fe(H2O)5SCN]2+ --- blood red [ SCN(-)... Fe here is Fe3+]

Nickel
[Ni(H2O)6]2+ --- light green >>>>> [Ni(NH3)6]2+ --- light blue

Chromium
[Cr(H2O)6]2+ ---blue
[Cr(H2O)6]3+ ---green/violet
[Cr(OH)6]3-  ---bright green
[Cr(H2O)5Cl]2+ -- light green >> [Cr(H2O)4Cl2]+ --- dark green

Cr2O7(2-) --- orange [ stable in acidic condition ; K2Cr2O7 ]
CrO4(2-) --- yellow [ stable in alkaline condition]

Manganese
[Mn(H2O)6]2+ --- light pink
MnO4- --- Purple [ Stable in acidic condition ; KMnO4]
MnO4(2-) --Green [ stable in alkaline condition]

------------------------------------------------------------------------------------

你选那些比较重要的来记起来，比如那些colour change when displacement of ligands occurs.
如果要记住全部的话，也不难。一个一个去imagine,这要看你的想象力。〔visualise 它们〕

[ 本帖最后由 darksider 于 9-11-2009 10:31 AM 编辑 ]

morphv02c01

原帖由 Dicardo 于 27-8-2009 11:32 AM 发表
so if it only written 'aqueous' , we can assume it is dilute ?

aqueous IS NOT equal to dilute

RachelT

我刚做完一个实验，titration of KA1,KA2,KA3。
想问有没有人知道为什么这个实验不需要用indicator？？
我好想知道答案。。
有人写因为KMnO4本身会变色，所以可以act as indicator，但是这个答案是错的耶。。
所以正确答案是？？？？

idontwant2b

有些印象，是不是关于那个dissociation的？

morphv02c01

你的titrant和titrate是什么?

jenyeh90

想問下哦，一個REACTION,
我要如何知道他是REVISIBLE OR NT?

EG:
A + B ﹣﹣﹣﹥ C    OR
A + B ﹤﹣﹣﹥ C

darksider

这我们要看那个reaction的entropy change.如果entropy change =0 ,那个reaction是reversible.

我们在stpm没有学到ｅｎｔｒｏｐｙ。

jenyeh90

那寫equation的時候要怎么辦？

darksider

原帖由 jenyeh90 于 2009/11/16 12:17 AM 发表
那寫equation的時候要怎么辦？

原来你问这个。。。如果那个arrow是有两个箭头的，那就是reversible reaction
如果一个箭头就irreversible.

A <-----> B

phoebie

请帮我解答

1.如果一个complex ion with 4 coordination number....我要怎样分他是tetrahedral 还是square planar???
plzzzzzzzzzzzzzzzz.....thxxxxxxxxxxxx

四月一日的小皮

low spin state和high spin state。
Tetrahedral and square planar complexes are the most common.
Small ions and/or large ligands prevent high coordination numbers (Mn(VII) or Cr(VI)).

Many d0 or d10 complexes have tetrahedral structures (only consider bonds).
exp MnO4- and [Ni(CO)4]

In stpm，you nd to know about square planar complex。

phoebie

楼上的。。。谢谢。。。可是我不明白耶。。。。有没有简单点的？？？

darksider

原帖由 phoebie 于 2009/11/19 01:55 PM 发表
楼上的。。。谢谢。。。可是我不明白耶。。。。有没有简单点的？？？

Why are they square planar?
When we talk about molecular geometry, we first consider their axial position (imagine it as y-axis going across the central atom) and the equatorial position (on the same plane as the central atom)

we know the VSEPR states that electron pairs will repel each other so that they are as far from each other as possible (minimum repulsion).

If there are four covalent bonding on the equatorial position and that the central atoms have 2 lone pairs on its axial position, its molecular shape will look like a square, thus square planar (square on the same plane) since lone pair is very small and cannot be seen.

So why don't the lone pair stay at the equatorial position? Why don't the covalent bond (dative bond) stay at the axial position?
To answer this u need to know in what kind of arrangement will they get minimum repulsion.
If you exchange one of the lone pair with one of the bonding pair, it will distort the square shape on the equatorial position, since repulsion btw lone pair -bonding pair > repulsion btw bonding pair- bonding pair, the square shape will be altered into a rhombus. This gives to non-minimum repulsion so it isn't possible.

The lone pairs must stay on the axial position in order for the repulsion to be minimum. Remember, electron pairs in the axial position will not have effect on the electron pairs in the equatorial position.

idontwant2b

原帖由 darksider 于 20-11-2009 12:57 AM 发表


Why are they square planar?
When we talk about molecular geometry, we first consider their axial position (imagine it as y-axis going across the central atom) and the equatorial position (on the  ...

我们老师说这种low spin / high spin / axial position 的东西不需要读，是真的吗？

darksider

原帖由 idontwant2b 于 2009/11/20 12:29 PM 发表


我们老师说这种low spin / high spin / axial position 的东西不需要读，是真的吗？

不会叫我们解释。但是如果要明白molecular geometry的话，就要懂，不然就一定要背。。。背这个比明白容易。。。

可以参考这个http://intro.chem.okstate.edu/1314F97/Chapter9/VSEPR.html
有animation,比较容易明白。

你可以那PCl5来当例子，过后你exchange a lone pair with one of the bondng and think about which bonding pair should be substituted to give minimum repulsion. (see-saw)

Then try substitute 2 lone pair and think they should replace which. (T shape)

Allison

PbO2 + conc.HCl 的product是什么？

darksider

原帖由 Allison 于 2009/11/20 03:10 PM 发表
PbO2 + conc.HCl 的product是什么？

PbCl4 and H2O... PbO2 is amphoteric... just treat it like an alkali when it reacts with acid.

ginny

Zaitsev's rule & Saytzeff's rule is same?