STPM化学专区

幸福蛋糕

好的..我会加油的~~!!

今年的ALUMINIUM 好象也很"红"~~~!!

幸福蛋糕

请问大家，
PCl5 + PCl 3 变什么？？

vinclam

原帖由 幸福蛋糕 于 2-12-2008 08:17 PM 发表
请问大家，
PCl5 + PCl 3 变什么？？

不会哦。。有这样的东西的 meh?
我还以为 PCl5 and PCl3 will react with ROH.. RCOOH.. 那些罢了..

幸福蛋糕

不懂列。。
我有做到这个问题。。

wahaha1

赞成~！！
我也爱化学~但很像有点给他们的回复吓倒下（讲笑啦）
加油把！！

x-treme

原帖由 幸福蛋糕 于 2/12/2008 08:17 PM 发表
请问大家，
PCl5 + PCl 3 变什么？？

PCL3+CL2=>PCL5

RachelT

中六化学最难的是？

Tarantino

原帖由 RachelT 于 24/12/2008 10:17 AM 发表
中六化学最难的是？

应该是Organic Chemistry吧？
有超多的reaction要记，记之前又要先弄明白概念（concept），要不然..

Ivanlsy

我朋友倒认为有机化学最简单！
见仁见智吧！

vinclam

原帖由 RachelT 于 24-12-2008 10:17 AM 发表
中六化学最难的是？

我觉得是 Physical 那些算的问题。很多时候都不知道要用什么方法，可能是缺少练习吧。。
Organic 的还好。。来来去去都是问变化和原因。。

星座小王子

原帖由 Ivanlsy 于 25-12-2008 12:24 AM 发表
我朋友倒认为有机化学最简单！
见仁见智吧！

我也这么觉得

organic最容易

然后是physical

然后才inorganic....

inorganic超难的，我读了n次，还是一知半解，太多东西要背了。。。

ps.但要注意咯，最近的stpm出越来越多inorganic了。。

RachelT

原帖由 星座小王子 于 29-12-2008 01:47 AM 发表


我也这么觉得

organic最容易

然后是physical

然后才inorganic....

inorganic超难的，我读了n次，还是一知半解，太多东西要背了。。。

ps.但要注意咯，最近的stpm出越来越多inorganic了。。

谢谢你们 我大概能了解了。

891108

我觉得inorganic最容易

丹尼斯九一

The frequencies,f,of the first four lines in the Lyman series are as follows.
24.53 × 10^14Hz
29.07 × 10^14Hz
30.66 × 10^14Hz
31.39 × 10^14Hz
Calculate the ionization energy of hydrogen using the information.
h=6.63 × 10^-34
我不會做這個…有誰可以解答???

wahaha1

请问有谁可以解释the uniqness of carbon atom AND hybridisation ??

darksider

原帖由 丹尼斯九一 于 2009/1/1 12:04 PM 发表
The frequencies,f,of the first four lines in the Lyman series are as follows.
24.53 × 10^14Hz
29.07 × 10^14Hz
30.66 × 10^14Hz
31.39 × 10^14Hz
Calculate the ionization energy of hydrogen using ...

Plot the graph of Difference in frequency against frequency.
你先找the difference in successive frequencies, eg, (29.07 - 24.53 ) x 10^14 Hz ... this value corresponds to 24.53 x 10^14 hz in the graph.

then you should find the value of frequency when difference in frequency = 0

Then use the value you found in this formula, energy = h x frequency (remember what u get here is jole per electron, you should give the answer in the form of kj per mole, so you have to multiply the answer by 6.02x10^23 and divide it by 1000 )

[ 本帖最后由 darksider 于 4-1-2009 11:24 AM 编辑 ]

darksider

原帖由 wahaha1 于 2009/1/3 03:58 PM 发表
请问有谁可以解释the uniqness of carbon atom AND hybridisation ??

Carbon exhibits allotropic properties, that is, it can exist in different forms under same condition, in this case, pressure and temperature.
They are graphite, diamond and also fullerene.

Graphite
When you take out a portion of graphite, you will see two layers of carbon rings connected by weak Van Der Waal's force.Because of this weak intermolecular force, graphite can be slided over easily. Hence, it can be used as lubricants.

The ring is formed by carbon using sp2 hybridisation , ie, one carbon forms covalent bonds with three neighbouring carbon atoms.
Since one valence electron is unused in the formation of bonds, it can move freely in graphite. This electron is said to be delocalised and it can conduct electricity. Therefore, it can be used as an electrode in electrochemical cell

Diamond
Diamond is another allotrope of carbon. It has a giant molecular structure which is why diamond has high melting points and boiling points. This is due to the strong covalent bonds in diamond. Carbons in diamond use sp3 hybridisation, ie, one carbon atom forms four covalent bonds with three neighbouring atoms. As a result, there is no delocalised electron and therefore, diamond cannot conduct electricity.

Diamond is usually made diamond-tipped tools such as cutting tools and also engraving tools. In addition, since diamond has high refractive index, it is made into jewellery products.

Fullerene (Buckminister fullerene)
Its structure is similar to that of a football, having 32 faces in which 12 faces are pentogonal and another 24 faces are hexagonal. It consists of 60 carbon atoms. Each carbon atoms in fullerene uses sp2 hybridisation, ie , forming covalent bonds with three neighbouring carbon atoms. Therefore, it has delocalised electrons and thus, it is an electric conductor.

With the mentioned properties, fullerene is usually used as superconductor , lubricant and also abrasive.

Hybridisation
Hybridisation is the mixing of atomic orbitals to form equivalent orbitals for bonding.
Why are atomic orbitals mixed? Before studying hybridisation, you need to understand VSEPR(Valence Shell Electron Pair Repulsion) first.
The basic principle of VSEPR theory is that valence electron pairs, whether they are bonding pair or lone pair, prefer to be as far from each other as possible. In other words, valence electron pairs always try to arrange themselves as far as possible from each other to MINIMISE the repulsion.

To explain the need of hybridisation using VSEPR, I use CH4 as an example. (Read this if you want to understand more, otherwise just ignore)
Look closer into the carbon atom in methane, it has 4 valence electrons. Its electronic configuration is 1s2 2s2 2px1 2py1.
Since it forms bond with the 1s orbital of another four hydrogen atoms, carbon atom will use its four valence electrons in its shell to form covalent bonds with them. Let say, Carbon atom is excited (when it receives energy, be it kinetic or heat energy), one of the electron in 2s jumps into 2pz which is empty. So the four electrons in our disposal are at 2s , 2px , 2py and 2pz respectively. Now it is ready to form bonds with hydrogen atoms , by pairing up them with electron found in 1s orbital of each hydrogen atoms.

So now, the four bonds formed are -
i)electron in 2s of carbon + electron in 1s of hydrogen
ii)electron in 2px of carbon + electron in 1s of hydrogen
iii)electron in 2py of carbon + electron in 1s of hydrogen
iv)electron in 2pz of carbon + electron in 1s of hydrogen               

As you know, methand has a tetrahedral shape with equal angles which is 109.5 deg.

Now you see, if using the orbitals I mentioned above, would it make them havin same angles in the shape?
The answer is not, because the size 2s orbital is smaller than that of 2px, 2py and 2pz, they simply cannot repulse each other to the same extent.

So what happens in the carbon atom of methane? How does it obtain its tetrahedral shape with four equal angles?
This is when hybridisation comes into play. Still remember that when carbon atom is excited, it has four electrons in four different orbitals (2s1, 2px1, 2py1 and 2pz1) ? These four electrons in these four orbitals are needed in the formation of methane, but they can't be used yet. In fact, they have to go through a process called HYBRIDISATION.

Ground state of carbon -  2s2 2px1 2py1 2pz0
Excited state of carbon -  2s1 2px1 2py1 2pz1 ( Cannot be used in formation of bonds, as explained above)
                                                            |
                                                            |  Hybridised (Since carbon needs to form four bonds, it uses sp3 (read as s - p - three) hybridisation )
                                                            |
                                                            |
    Hybridised state         sp3 sp3   sp3 sp3  ( each sp3 orbitals carries one electron, in this case)

These four sp3 orbitals are degenerate, meaning they have equal energy level. Four of them will each combine with the 1s orbital of hydrogen and they form methane.

There are three types of hybridisation, namely sp, sp2 and sp3.  ( read as s-p , s - p - two , s - p - three , very simple, sp because 1 s orbital combines with 1 p orbital , sp2 because 1 s orbital combines with 2 p orbital and same for sp3)

If carbon only forms 2 bonds, it uses sp hybridisation, if it only forms 3 bonds, it uses sp2 hybridisation.

Anything I explain wrongly pls correct me, thanks!

[ 本帖最后由 darksider 于 4-1-2009 12:36 PM 编辑 ]

卡莉。谢

chemistry 的calculation 就快把我杀死了～

暴杀·憾雨泪

hydrochloric acid是不是ionic bond来的？
H和Cl都是非金属，
但为什么还能dissociate into ions之类的?
而且还能溶在water里，polarising的不是吗？

然后H是第几组的元素来的？

星星之玲

这是physical chemistry 的chapter12 phase equilibrium问题谁能帮我算一下啊?谢谢!

The partition coefficient of a substance X between ether and water is 8.0 .
An  aqueous solution containing 5.0g of X in 100cm^3 of water is extracted with 100cm^3 of ether .
What is the maximum mass of X that can be extracted into the ether layer?


The answer is 4.44g  who can show me the working...please! thank...