STPM 化学问题 马拉松！

紫色的黑蝴蝶

Air contains 20% volume by oxygen.
If V cm3 of air is mixed with V cm3 of pure oxygen at the same pressure,that is at 2x 10^5 Pa,what will be the partial pressure of oxygen in the gaseous mixture?

lowch1

原帖由 紫色的黑蝴蝶 于 10-11-2006 08:54 PM 发表


A neutral compound Z, has the empirical formula, Co(Cl)x(NH3)y. The percentage conposition by mass in the complex is as follows.
Co, 23.52%
N, 28.00%
Cl, 42.53%
H, 5.95%
When an aqueous so ...

答案满准确的。。

lowch1

做摸好象很乱将的。到底轮到那一题？

JamesTea

原帖由 lowch1 于 11-11-2006 01:55 AM 发表
做摸好象很乱将的。到底轮到那一题？

就给紫色黑蝴蝶先吧，到他那题了

紫色的黑蝴蝶

Air contains 20% volume by oxygen.
If V cm3 of air is mixed with V cm3 of pure oxygen at the same pressure,that is at 2x 10^5 Pa,what will be the partial pressure of oxygen in the gaseous mixture?

lowch1

原帖由 紫色的黑蝴蝶 于 11-11-2006 02:06 AM 发表
Air contains 20% volume by oxygen.
If V cm3 of air is mixed with V cm3 of pure oxygen at the same pressure,that is at 2x 10^5 Pa,what will be the partial pressure of oxygen in the gaseous mixture?

er... try only

partial pressure of O2=((0.2V+V)/2V)* 2x10^5 Pa
                      = 120000Pa

lowch1

现在应该是James的那题了吧？

紫色的黑蝴蝶

Aqueous ammonia is gradually added to an aqueous solution containing a mixture of iron(II),copper(II) and zinc ions>Which of these ions will form a precipitate?

请解释喔..

lowch1

原帖由 lowch1 于 11-11-2006 02:13 AM 发表


er... try only

partial pressure of O2=((0.2V+V)/2V)* 2x10^5 Pa
                      = 120000Pa

其实我的答案到底对不对？

枫之子

怎么只有你们三人？我都不知你们再问什么，死定了

lowch1

原帖由 JamesTea 于 11-11-2006 12:04 AM 发表
Q79 :

Ammonia is a very important ingrediant in the manufacture of fertilizers. Its synthesis from nitorgen may be represented by the following equations.

N2 (g)   +  3H2(g)   <----->   2NH3(g)

(i)  why is a high pressure used in this process ?
(ii) name the catalyst used in the process and explain its action .

就这题吧。。好象还没答。。

JamesTea

原帖由 lowch1 于 11-11-2006 10:32 PM 发表


就这题吧。。好象还没答。。

紫色的黑蝴蝶不是已经回答了吗 ？？我也有补加一些 points


Next Question :

Explain the following observations, by giving the structural formula of possible species involved .

I) Three crystalline compounds X Y Z with the molecular formula CrCl3.6H2O is purple , light green and dark green respectively. When these three compounds in the same amount are reacted separately with excess aqueous silver nitrate at room temperature, the mass of the white precipitate formed is in the ratio of 3:2:1.

II) When a solution of ammonium metavanadate,  NH4VO3 , in the dilute sulphuric acid is shaken with zinc, the colour of the solution changes from yellow to blue, then green, and finally purple.

dunwan2tellu

I) Three crystalline compounds X Y Z with the molecular formula CrCl3.6H2O is purple , light green and dark green respectively. When these three compounds in the same amount are reacted separately with excess aqueous silver nitrate at room temperature, the mass of the white precipitate formed is in the ratio of 3:2:1.

white ppt = AgCl .
Ratio of 3:2:1 means that the ligand of compounds X,Y,Z are Cl3 ,Cl2 , Cl respectively . Hence X = [Cr(H2O)6]Cl3 ; Y = [CrCl(H2O)5]Cl2 ; Z = [CrCl2(H2O)4]Cl

II) When a solution of ammonium metavanadate,  NH4VO3 , in the dilute sulphuric acid is shaken with zinc, the colour of the solution changes from yellow to blue, then green, and finally purple.

我猜测是 V(5+) is yellow colour and is reduced by dilute H2SO4 and zinc into V(4+) (blue) -->V(3+) (green) -->V(2+) (purple) .

QooLuo

有一题不是很会,题目大概是这样：
based on the electronic configuration of the nucleus of nitrogen atom, explain why NH4OH cannot exist.

dunwan2tellu

原帖由 JamesTea 于 10-11-2006 11:54 PM 发表







1) answer is A . F is the most electronegative element ,therefore the bond between F2 molecule are held strongly . C6H5OH is ortho and para directing compound and it will reacts with  ...

我觉得 A 是因为 F2 和 Br2 都是 oxidising agent . 所以他们俩不可能 react

F2 + Br2 --> ?? nothing

JamesTea

原帖由 dunwan2tellu 于 13-11-2006 07:48 PM 发表

white ppt = AgCl .
Ratio of 3:2:1 means that the ligand of compounds X,Y,Z are Cl3 ,Cl2 , Cl respectively . Hence X = Cl3 ; Y = Cl2 ; Z = Cl



我猜测是 V(5+) is yellow colour and is reduce ...

答对了 ^^

JamesTea

原帖由 dunwan2tellu 于 13-11-2006 09:59 PM 发表


我觉得 A 是因为 F2 和 Br2 都是 oxidising agent . 所以他们俩不可能 react

F2 + Br2 --> ?? nothing

哦，原来是酱的解释 ，没有想到是这各 explanation

JamesTea

原帖由 QooLuo 于 13-11-2006 08:02 PM 发表
有一题不是很会,题目大概是这样：
based on the electronic configuration of the nucleus of nitrogen atom, explain why NH4OH cannot exist.

electronic configuraton of Nitrogen atom and  Hydrogen atom:

N : 1s2 2s2 2p3
H : 1s1

ammonia is form when each of the 3 H atoms are sharing a single electron with 2p orbital of N atom forming NH3.
when NH3 is dissolve in water , the lone lone pair of 2s in Nitrogen willl be donated to the H atom of water molecule forming NH4+ ion and leave out OH- ion
notice that all the orbitals in N atom are occupied, that is the 2p orbital of Nitrogen is now fully-filled . There is no 2d orbitals therefore the OH- ion cannot donate its lone pair to the NH4+ ion . So this is why NH4OH does not exist .
To indicate ammonia in aqueous state, NH3(aq) is normally used .




应该是这样吧 ？

[ 本帖最后由 JamesTea 于 14-11-2006 12:02 AM 编辑 ]

ronloh94

如果这样解释，为什么NH4Cl能exist？奇怪~

dunwan2tellu

原帖由 JamesTea 于 14-11-2006 12:00 AM 发表






electronic configuraton of Nitrogen atom and  Hydrogen atom:

N : 1s2 2s2 2p3
H : 1s1

ammonia is form when each of the 3 H atoms are sharing a single electron with 2p orbital of N ...

我相信 NH4(+) 和 OH(-) 之间应该是 electrostatic force 吧？不会和 dative bond 有关。我猜题目是要问为什么 ammonium hydroxide 只能 exist as NH4(+) aq 和 OH(-) aq 而不是 NH4OH aq ??