STPM 化学问题 马拉松！

Smithy

因为如果温度高,Rate of Reaction的提高会造成不只Nitrobenzene的诞生,
还会有 dinitobenzene 和 trinitrobenzene 。
（我不知道解释对不对，我不太会解释，惨～ 考试死了)

问题十四
Claculate the pH of a mixture of 100cm^3 of 1.00 x 10^-2 moldm-3 HCL and 100cm^3 of 5.00 x 10-3 mol dm^-3 NAOH

dunwan2tellu

原帖由 Smithy 于 19-5-2006 05:48 PM 发表
因为如果温度高,Rate of Reaction的提高会造成不只Nitrobenzene的诞生,
还会有 dinitobenzene 和 trinitrobenzene 。
（我不知道解释对不对，我不太会解释，惨～ 考试死了)

问题十四
Claculate the pH of a ...

大致上如你所解释的，因为我们不要 dwisubstitution of nitrate ion into benzene ring

Q14)
acid 的 mol > base 的 mol .所以 [H+]  excess 0.5 x10^(-3) mol

因此 pH of solution = -Log[H+] = 3.30

问题 15
When pure water boils , how does this affects its pH ?

[ 本帖最后由 dunwan2tellu 于 19-5-2006 06:05 PM 编辑 ]

Smithy

pH of Pure Water will Decrease when it boiled
it is because when the temperature increase ,
more water will dessociates into H+ and OH-,
the cencentration of H+ and OH- will increase and >10^-7 mol dm^-3.
Therefore, pH and pOH will become less that 7.

Question 16
What will happen when inert gas is added to a endothermic reaction at constant preassure ?

dunwan2tellu

原帖由 Smithy 于 21-5-2006 01:22 PM 发表
pH of Pure Water will Decrease when it boiled
it is because when the temperature increase ,
more water will dessociates into H+ and OH-,
the cencentration of H+ and OH- will increase and >10^ ...

加 Inert gas 的话，partial pressure of each species in original mixture 会减少。至于 endothermic 或 exothermic process , 我觉得应该没有关系吧？不知道对不对

hamilan911

原帖由 Smithy 于 21-5-2006 01:22 PM 发表
pH of Pure Water will Decrease when it boiled
it is because when the temperature increase ,
more water will dessociates into H+ and OH-,
the cencentration of H+ and OH- will increase and >10^ ...

加inert gas会使partial pressure减少。
endo 或exo不会受影响。
effect of lower pressure only depends on number of mole of product and reactants.

暂时没想到题目。

dunwan2tellu

问题 17

Write out the chemical reaction to prepare trichloromethylbenzene from methlybenzene . State also the reagent and conditions for the reaction .

[ 本帖最后由 dunwan2tellu 于 23-5-2006 11:42 AM 编辑 ]

多普勒效应

methylbenzene + Cl2
Catalyst 是 FeCl3.

可以吗？

dunwan2tellu兄和hamilan兄有参加 KKKM 吗？

dunwan2tellu

正确一点应该是 excess Cl2 , 因为要变成 " trichloro " .

我的班所有同学都有参加 Quiz Kimia Kebangsaan .请问你是指这个吗？

既然答对了，就贴个题目上来吧！

[ 本帖最后由 dunwan2tellu 于 23-5-2006 11:45 AM 编辑 ]

gsan

问题 18

Why the melting point of MgO is greater than Aluminium Oxide?

dunwan2tellu

原帖由 gsan 于 23-5-2006 12:35 PM 发表
问题 18

Why the melting point of MgO is greater than Aluminium Oxide?

照理来说应该是看 lattice energy 不过 MgO 的 lattice 却小过 Al2O3 ,所以能解释的就是 MgO has more closely packed lattice .

问题 19

Explain why AlCl3 is covalent bond rather than ionic bond?

哈贼

原帖由 dunwan2tellu 于 23-5-2006 01:06 PM 发表


照理来说应该是看 lattice energy 不过 MgO 的 lattice 却小过 Al2O3 ,所以能解释的就是 MgO has more closely packed lattice .

问题 19

Explain why AlCl3 is covalent bond rather than ionic bond?

it is due to the small difference of electronegativity between Al atom and Cl atom.therefore,it has more covalent characteristic than ionic characteristic.it is more likely to be covalent bond even it has ionic characteristic.

问题20：

Explain why the conductivity of metalloid increases when temperature increases?

dunwan2tellu

停了那么久是时候该继续了！

我觉得当温度提高时，more ion will move freely since they have energy .So more easier to conduct electricity ??

有错情纠正！

问题 21
What is the most common metal in Earth's crust?
A. copper
B. lead
C. iron
D. aluminium

哈贼

原帖由 dunwan2tellu 于 30-5-2006 03:20 PM 发表
停了那么久是时候该继续了！

我觉得当温度提高时，more ion will move freely since they have energy .So more easier to conduct electricity ??

有错情纠正！

metalloid is semiconductor.electron are not conducted by ion.as the temperature increase,more electrons may acquire enough energy to jump from valence band to conduction band.hence,higher thermal energy,more electrons can make the transtion.(refer to band theory)

[ 本帖最后由 哈贼 于 30-5-2006 11:17 PM 编辑 ]

dunwan2tellu

原帖由 dunwan2tellu 于 30-5-2006 03:20 PM 发表
停了那么久是时候该继续了！

我觉得当温度提高时，more ion will move freely since they have energy .So more easier to conduct electricity ??

有错情纠正！

问题 21
What is the most common meta ...

没有继续太可惜了....
Q21 ) D Aluminium

问题 22

When a compound X is refluxed with propanol , two compound Y,Z with molecular formula (C_6)(H_12)(O_2) and (C_5)(H_10)(O_2) respectively is formed . Identify compound X .

独帆

1.Kenapa CH3–CH–COOH mungkin wujud dalam campuran rasemik secara semulajadi?          |
           Cl            

2. O = C – O – C3H7
       |            
  CH3—CH2         NAMA MOLEKUL INI IALAH …..a)1-propil propanoat
                                              b)2-propil propanoat
                                         a) dan b) yang mana satu betul?

3.Apabila 10 cm3 suatu sebatian M diletupkan dalam 100 cm3 oksigen dan disejuka n ke  suhu bilik,isipadu gas ialah 95 cm3.isipadu ini dikurangkan kepada 75 m3 apabila digoncangkan dengan larutan kalium hidroksida.M ialah……
Jawapan: CH3 – CHO

[ 本帖最后由 独帆 于 17-7-2006 03:23 AM 编辑 ]

dunwan2tellu

.Kenapa CH3–CH–COOH mungkin wujud dalam campuran rasemik secara semulajadi?          |
           Cl            

if it is racemic mixture then it has chiral carbon , 看看
      Cl
      |
CH3 - C - COOH
      |
      H

所以是 racemic mixture .

2. O = C – O – C3H7
       |            
  CH3—CH2         NAMA MOLEKUL INI IALAH …..a)1-propil propanoat
                                              b)2-propil propanoat
                                         a) dan b) yang mana satu betul?

这是 ester 。照你的写法只能知道是 propyl propanoat.

3.Apabila 10 cm3 suatu sebatian M diletupkan dalam 100 cm3 oksigen dan disejuka n ke  suhu bilik,isipadu gas ialah 95 cm3.isipadu ini dikurangkan kepada 75 m3 apabila digoncangkan dengan larutan kalium hidroksida.M ialah……
Jawapan: CH3 – CHO

你确定没有少给资料吗？

独帆

原帖由 dunwan2tellu 于 17-7-2006 04:55 PM 发表

if it is racemic mixture then it has chiral carbon , 看看
      Cl
      |
CH3 - C - COOH
      |
      H

所以是 racemic mixture .

这是 ester 。照你的写法只能知道是 propyl propanoat.
...

answer is 2-propil propanoat.why is 2?

Apabila 10 cm3 suatu sebatian M diletupkan dalam 100 cm3 oksigen dan disejuka n ke  suhu bilik,isipadu gas ialah 95 cm3.isipadu ini dikurangkan kepada 75 m3 apabila digoncangkan dengan larutan kalium hidroksida.M ialah……
A. CH3 – CHO
B. CH3CH2OH
C.CH3COOH
D.CH2=CH2

ANSWER:A .HOW TO DO?

         H
         |
benzena--C--O--H
         |
         H
apakah sudut ikatan H--C--O?

tertib keasidan menurun : CH2ClCOOH > CH2BrCOOH > CH3COOH > C6H5OH > CH3OH
mengapa?

[ 本帖最后由 独帆 于 18-7-2006 03:21 PM 编辑 ]

happytomato

Cl is an electron-withdrawing group, so it increase the acidity of CH2COOH.CH3 is an electron-donating group, so it stronger the O-H bond in COOH,hence it becomes less acidicty compare to CH2COOH.In the carboxylate ion(R-COO-), the negative charge is delocalised over both the electronegativity oxygen atoms, so it is more acidity than phenol.Phenol is more acidity than alcohol because benzene ring is an electron-withdrawing group.

electron-withdrawing group: increase acidicty
                            Eg: benzene ring, NO2
electron-donating group:decrease acidicty
                        Eg: CH3, OH
我这样解释对吗?

happytomato

Cl is an electron-withdrawing group, so it increase the acidity of CH2COOH.CH3 is an electron-donating group, so it stronger the O-H bond in COOH,hence it becomes less acidicty compare to CH2COOH.In the carboxylate ion(R-COO-), the negative charge is delocalised over both the electronegativity oxygen atoms, so it is more acidity than phenol.Phenol is more acidity than alcohol because benzene ring is an electron-withdrawing group.

electron-withdrawing group: increase acidicty
                            Eg: benzene ring, NO2
electron-donating group:decrease acidicty
                        Eg: CH3, OH
我这样解释对吗?

happytomato

Cl is an electron-withdrawing group, so it increase the acidity of CH2COOH.CH3 is an electron-donating group, so it stronger the O-H bond in COOH,hence it becomes less acidicty compare to CH2COOH.In the carboxylate ion(R-COO-), the negative charge is delocalised over both the electronegativity oxygen atoms, so CH3COOH more acidity than phenol.Phenol is more acidity than alcohol because benzene ring is an electron-withdrawing group.

electron-withdrawing group: increase acidicty
                            Eg: benzene ring, NO2
electron-donating group:decrease acidicty
                        Eg: CH3, OH
我这样解释对吗?