STPM 化学问题 马拉松！

nikuang04

原帖由 huhuxboy 于 2-7-2007 22:49 发表
来推动一下这楼。。。
不然那么冷清清的

再一题：
(a) Write the mechanism for the following chlorination reaction.
      CH3CH2CH3 + 2Cl2 ----> CH3CH(Cl)CH2Cl + 2HCl

(b) Explain the form ...

2004年STPM题目
想问一下真正STPM的题目arrow上面有没有放hv（ultraviolet)?
the mechanism involved is free radical substitutuon.
initiation: Cl2 --->2Cl 。

Propagation:
CH3CH2CH3 + Cl。 ----〉CH3CHCH3。+HCl
CH3CHCH3。+ Cl2 ------〉CH3CHClCH3 + Cl。
CH3CHClCH3 + Cl。-----〉CH3CHClCH2。 + HCl
CH3CHClCH2。+ Cl2 -----〉CH3CHClCH2Cl + Cl。

Termination:
Cl。+ CH3CHClCH2。------〉CH3CHClCH2Cl

2个CH3CHCH3。就变成(CH3)2CHCH(CH3)2

nikuang04

我也来
An element has the following successive ionissation energies/kJ mol-1
762,1540,3300,4390,8950,11900
In which group of the periodic table is this element most likely to be found?
A.Group1
B.Group2
C.Group13
D.Group14
E.Group15

huhuxboy

D. Group 14 ???

nikuang04

原帖由 huhuxboy 于 4-7-2007 19:44 发表
D. Group 14 ???

对
因为第4和第5的IE相差最多
这里好冷清啊

Reaction Kinetics
What is the expression of the half life of a first order reaction?
A.ln2/k
B.1/ak where a is the initial concentration
C.a/2k

jeremy3232

Answer is A. half-life= ln2/k

B. 1/ak where a is the initial concentration (second order)

C. C.a/2k (zero order)

nikuang04

原帖由 jeremy3232 于 4-7-2007 21:00 发表
Answer is A. half-life= ln2/k

B. 1/ak where a is the initial concentration (second order)

C. C.a/2k (zero order)

全对
thermochemistry
which of the following ions has the most exothermic enthalpy change of hydration?
A.Na+
B.K+
C.Mg2+
D.Ca2+
E.Al3+

huhuxboy

E Al3+.....

huhuxboy

Which of the following exerts the highest pressure?
A. 1 mol of N2 at 0'C in 11.2dm^3
B. 1 mol of N2 at 27'C in 22.4dm^3
C. 1 mol of H2O at 27'C in 1dm^3
D. 1 mol of C4H10 at its normal boiling point.

nikuang04

原帖由 huhuxboy 于 5-7-2007 00:07 发表
E Al3+.....

对
因为charge最高和ionic radius最小

原帖由 huhuxboy 于 5-7-2007 00:12 发表
Which of the following exerts the highest pressure?
A. 1 mol of N2 at 0'C in 11.2dm^3
B. 1 mol of N2 at 27'C in 22.4dm^3
C. 1 mol of H2O at 27'C in 1dm^3
D. 1 mol of C4H10 at its normal boili ...

答案是不是A？这题好像做过，可是忘记怎样做了
为什么不是D？



再来！
What  are the mechanisms of the following reactions?
1. nitration of benzene
2.addtion of halogen to alkene
3.chlorination of alkane
4.hydrolysis of haloalkane

[ 本帖最后由 nikuang04 于 5-7-2007 02:02 PM 编辑 ]

huhuxboy

因为1 mol of C4H10 at its normal boiling point 的 pressure is equal to the atmospheric pressure as the condition is at normal boiling point.

jeremy3232

1. nitration of benzene (electrophilic substitution)
2.addtion of halogen to alkene (electrophilic addition)
3.chlorination of alkane (free radical substitution)
4.hydrolysis of haloalkane (nucleophilic substitution)

zxteh

Which of the following group is more electron withdrawing group?
A.CH3
B.NO2
C.COOH
D.OH

[ 本帖最后由 zxteh 于 14-7-2007 11:20 AM 编辑 ]

nikuang04

原帖由 zxteh 于 13-7-2007 17:26 发表
Which of the following group is electron withdrawing group?
A.CH3
B.NO2
C.COOH
D.OH

是B吗？
你在问arenes吧？感觉上你应该问resonance effect 或者是inductive effect
因为OH 也是electron withdrawing group (inductively)

which species acts as the electrophile in the addtion of hydrogen bromide to ethene?

[ 本帖最后由 nikuang04 于 13-7-2007 05:37 PM 编辑 ]

jiko

原帖由 zxteh 于 13-7-2007 05:26 PM 发表
Which of the following group is electron withdrawing group?
A.CH3
B.NO2
C.COOH
D.OH

我觉得Ｂ／Ｃ咯
ＯＨ跟ｂｅｎｚｅｎｅ时好像会变成ｄｏｎａｔｉｎｇ的。。。
ＮＯ２和ＣＯＯＨ好像都是ｅｌｅｃｔｒｏｎ　ｗｉｔｈｄｒａｗｉｎｇ哦。。。

jiko

原帖由 nikuang04 于 13-7-2007 05:35 PM 发表


是B吗？
你在问arenes吧？感觉上你应该问resonance effect 或者是inductive effect
因为OH 也是electron withdrawing group (inductively)

which species acts as the electrophile in the addtion of ...

ＨＢｒ？？？？？

jovene

which species acts as the electrophile in the addtion of hydrogen bromide to ethene?


hydrogen bromide has a permanent dipole
When ethene  reacts with hydogen bromide,
step 1: the attacks H+ ion in HBr on the double bond to form a carbonium ion.
step 2: the attack of the negative ion,the bromide ion (Br-) on the carbonium ion to form bromoethane.

therefore, the electrophile izit should be H+?

对吗？

huhuxboy

我觉得是HBr 是 electrophile
因为是整个HBr attack ethene double bonds, not the H+ ions from HBr attack ethene. HBr has permanent dipole with H is delta positive and Br is delta negative. When HBr attacks ethene, electrons from double bond attack H from HBr causing heterolytic fission of HBr with the bonded electrons move to the Br, producing Br-. Then also corbonium ions are produced. Then the Br- and the carbonium ion react immediately as carbonium ions are unstable.
Therefore, electrophile is HBr.

我觉得是酱

nikuang04

原帖由  jiko 于 13-7-2007 20:06 发表

我觉得Ｂ／Ｃ咯
ＯＨ跟ｂｅｎｚｅｎｅ时好像会变成ｄｏｎａｔｉｎｇ的。。。
ＮＯ２和ＣＯＯＨ好像都是ｅｌｅｃｔｒｏｎ　ｗｉｔｈｄｒａｗｉｎｇ哦。。。

所以我说题目应该写的清除写
4个选择中只有CH3是donating
OH是inductive electron withdraw，但是它有lone pair，can interact with the delocalized pi electron in the benzene ring.所以又resonance electron donating.

NO2 和COOH都是resonance electron withdrawing 吧？

原帖由  jiko 于 13-7-2007 20:07 发表

ＨＢｒ？？？？？

原帖由 huhuxboy 于 13-7-2007 20:54 发表
我觉得是HBr 是 electrophile
因为是整个HBr attack ethene double bonds, not the H+ ions from HBr attack ethene. HBr has permanent dipole with H is delta positive and Br is delta negative. When HBr ...

对啦。就是HBr。
既然mechanism 叫electrophilic addition
其实intermediate的carbocation也是electrophile



再来！
Phase equilibria:
A mixture of ethanol and water shows positive deviation from raoult's law.
Is the  boiling point composition curve for a mixture of ethanol and water show maximum or minimum?

The azeotrope of the solution contains 95.6% of ethanol.
What is the first distillate  of the 50% of the mixture?

想请问各位，你们学校的化学教到哪里了？感觉上我们学校好像很慢这样
我们才教完physical chemistry + organic 到 alcohol一半 + inorganic的group 2 罢了

zxteh

原帖由 nikuang04 于 13-7-2007 05:35 PM 发表


是B吗？
你在问arenes吧？感觉上你应该问resonance effect 或者是inductive effect
因为OH 也是electron withdrawing group (inductively)

which species acts as the electrophile in the addtion of ...

true..是B.

zxteh

表于 13-7-2007 08:24 PM  资料  个人空间  短消息  加为好友   
which species acts as the electrophile in the addtion of hydrogen bromide to ethene?


hydrogen bromide has a permanent dipole
When ethene  reacts with hydogen bromide,
step 1: the attacks H+ ion in HBr on the double bond to form a carbonium ion.
step 2: the attack of the negative ion,the bromide ion (Br-) on the carbonium ion to form bromoethane.

by following Markonikoff's rule
which C have more H atom,
the H will go through to the C which have more H atom
n then the Br will go to the C which have less H atom..

But in this case both C have same amount of H atom...
then how..?

it must follow the Stezeff's rule,
H atom will go to the H atom in the upper position
n Br will go to the lower position of C atom..

the electrophile is HBr...
Is it true...

[ 本帖最后由 zxteh 于 14-7-2007 11:21 AM 编辑 ]