STPM 化学问题 马拉松！

ronloh94

问题 63

An aqueous solution of ammonium chloride has a pH < 7.0 because

1  the ammonium ion is a Bronsted-Lowry acid
2  the chloride ion reacts with water to form hydrochloric acid
3  of the presence of coordinate bond in the ammonium ion.

dunwan2tellu

An aqueous solution of ammonium chloride has a pH < 7.0 because

1  the ammonium ion is a Bronsted-Lowry acid
2  the chloride ion reacts with water to form hydrochloric acid
3  of the presence of coordinate bond in the ammonium ion.

1
NH4(+) <==> NH3 + H(+)

2,3应该没关系吧？

Bernardtan87

原帖由 ronloh94 于 10-10-2006 03:30 PM 发表

哪里有得看正式的skema？

我没看到skema.但我老师有给我们答案。那本six years series有蛮多错误的

dunwan2tellu

原帖由 Bernardtan87 于 13-10-2006 05:58 PM 发表


我没看到skema.但我老师有给我们答案。那本six years series有蛮多错误的

针对哪个题目，我问了我学校的老师。他说如果题目只是说ｉｓｏｍｅｒ　而不是ｇｅｏｍｅｔｒｉｃａｌ／　ｏｐｉｃａｌ／ｓｔｒｕｃｔｕｒａｌ　ｉｓｏｍｅｒ　的话，我们要考虑全部可能。　

STPM没有学ethyne吗？

那抱歉，不过yawwu答对了

[ 本帖最后由 xiaoqiang88 于 15-10-2006 01:32 PM 编辑 ]

ss_sky87

原帖由 xiaoqiang88 于 15-10-2006 01:30 PM 发表
STPM没有学ethyne吗？

那抱歉，不过yawwu答对了

有啊．．．ｏｒｇａｎｉｃ的。
R-CHO 不是aldehyde麽？
如果沒記錯的話。

dunwan2tellu

问题 64

What deviation does a mixture of solution of propanone and trichloromethane show by Raoult's Law ? Explain your answer .

C011201

- Mixture of propanone and trichloromethane is a non-ideal solution which show negative Raoult's law.
- The total vapour pressure of the solution abtain is less than the total vapour pressure calculate from Raoult's Law.
- This is because the intermolecular force between propanone and trichloromethane in the mixture is stronger than the intermolecular force between propanon-propanone in pure propanone and the intermolecular force between trichloromethane-trichloromethane in pure trichloromethane.
- The intermolecular force between trichloromethane-trichloromethane in pure trichloromethane is weak Van der Waals force
- The intermolecular force between propanon-propanone in pure propanone is weak Van der Waals force.
- But the the intermolecular force between propanone and trichloromethane  is stronger hydrogen bonding.

Hydrogen bonding is stonger than Van der Waals force

dunwan2tellu

原帖由 C011201 于 16-10-2006 03:12 PM 发表
- Mixture of propanone and trichloromethane is a non-ideal solution which show negative Raoult's law.
- The total vapour pressure of the solution abtain is less than the total vapour pressure calc ...

哈哈。除了一些小小的 spelling mistake 之外，其他都 ok

下一题。

C011201

What deviation does a mixture of solution of methanol and ethanol show by Raoult's Law ? Explain your answer .

dunwan2tellu

原帖由 C011201 于 17-10-2006 10:47 PM 发表
What deviation does a mixture of solution of methanol and ethanol show by Raoult's Law ? Explain your answer .

-Methanol and ethanol does not show deviation from Raoult's Law .
-The mixture of the solution is ideal solution .
-Intermolecular force between the mixture is same as the intermolecular force between the pure liquid.
-The total vapour pressure of the mixture is equal to the total vapour pressure of each pure liquid .

dunwan2tellu

问题66

It is obsevered that the enthalphy change of solution of Berilium Sulphate is exothermic whereas the enthalphy change of solution of Barium Sulphate is endothermic . Explain this observation  .

[ 本帖最后由 dunwan2tellu 于 18-10-2006 03:34 PM 编辑 ]

ronloh94

原帖由 dunwan2tellu 于 18-10-2006 02:56 PM 发表
问题66

It is obsevered that the enthalphy change of solution of Berilium Sulphate is exothermic whereas the enthalphy change of solution of Barium Sulphate is endothermic . Explain this observation  .

Decrease down the group2, the latice energy and the hydration energy decrease. However, the lattice energy does not decrease much because the sulphate ion is much bigger then M(2+) ion,so the inter-ionic distance is almost constant.Hence, the decrease is small.
So, the inter-ionic distance of Berilium Sulphate and Barium Sulphate is almost
the same.

But the hydration energy of the cations decrease(less exothermic) much significantly as the ionic radius of cations increases (charge density decreases) down the group 2.
So, the hydration energy of the Be(2+) is much more exothermic than that of Ba(2+)

The enthalpy change of solution= -(enthalpy change of lattice energy[almost constant])+( enthalpy change of hydration[become less exothermic down the group])

therefore the enthalpy of solution become less exothermic down the group.

thus, the enthalphy change of solution of Berilium Sulphate is exothermic whereas the enthalphy change of solution of Barium Sulphate is endothermic .

ronloh94

我讲到乱七八糟，如果错告诉我。


问题67

Explain why aluminium carbonat cannot be prepared by mixing aqueous solutions of sodium carbonate and aluminium salts. Write the equation of the reaction involved.   [3 marks]

[ 本帖最后由 ronloh94 于 19-10-2006 08:45 PM 编辑 ]

dunwan2tellu

原帖由 ronloh94 于 19-10-2006 08:31 PM 发表
我讲到乱七八糟，如果错告诉我。


问题67

Explain why aluminium carbonat cannot be prepared by mixing aqueous solutions of sodium carbonate and aluminium salts. Write the equation of the reac ...

我只是猜测是不是因为
Al(3+) ion has high charge density and can polarise the electron from CO3(2-) and hence weaken the C-O bond causing Al2(CO3)3 to decompose into Al2O3

Al2(CO3)3 --> Al2O3 + 3CO2

ronloh94

原帖由 dunwan2tellu 于 20-10-2006 10:22 AM 发表


我只是猜测是不是因为
Al(3+) ion has high charge density and can polarise the electron from CO3(2-) and hence weaken the C-O bond causing Al2(CO3)3 to decompose into Al2O3

Al2(CO3)3 -->  ...

错~这题蛮难的。我给答案吧。

问题67的答案如下：
When aluminium salts dissolve in water, [Al(H2O)6](3+) ions are formed. Due to the high polarising power of Al(3+) ion, H3O(+) ions are formed as follows:
[Al(H2O)6](3+) + H2O ->  [Al(H2O)5 OH](2+) + H3O(3+)


When a bes like Na2CO3 is added, more H(+) ions are eliminated and [Al(OH)3.3(H2O)](s) is precipitated instead of Al2(CO3)3 (s)

2[Al(H2O)6](3+) (aq) + 3CO3(2-) (aq) ->  2[Al(OH)3.3(H2O)] (s) + 3H2O (l)+ 3CO2 (g)

Bernardtan87

对不起，借贴用一下。
请问如果observation要写
gas yang MENGERUHKAN air kapur
英文怎么写？

dunwan2tellu

原帖由 Bernardtan87 于 23-10-2006 09:50 AM 发表
对不起，借贴用一下。
请问如果observation要写
gas yang MENGERUHKAN air kapur
英文怎么写？

gas which turns lime water chalky .

Bernardtan87

原帖由 dunwan2tellu 于 23-10-2006 11:18 AM 发表


gas which turns lime water chalky .

谢谢你啦！！

dunwan2tellu

问题 68
Which of the following is/are true about electrolysis?

A.Reduction occurs at anode .
B.Electron travels from cathode to anode in external cicuit.
C.The readiness of a cation to discharge while electrolysis is inversely proportional to the reactivity of the metal
D.the amount of substance obtained while electrolysis is directly proportional to quantity of electricity used and its ionic charge.

[ 本帖最后由 dunwan2tellu 于 26-10-2006 04:23 PM 编辑 ]