STPM 化学问题 马拉松！

hvaly

原帖由 jayck 于 24-8-2006 11:05 AM 发表
问题25In the line emission spectrum of hydrogen , how many lines can be accounted for by all the possible electron transition between the five levels of lowest energy within the atom.

A. 4                        B.  ...

D 10 gua

hvaly

原帖由 jayck 于 24-8-2006 10:48 AM 发表


答案是B
When electron falls from a higher level to a lower level ,excess energy is given out as radiation with certain frequency.
And this frequency is determine by the two level involve in t ...

这题我有做过。我也认为答案是C。结果答案是B。我觉得两个答案都好像是对的。有谁可以清清楚楚的告诉我为何答案是B而不是C？哪一个较tepat?

hvaly

好吧！是时后进入 23 ... [/quote]

Question 23 的答案是不是这样？
propan-2-ol 先undergoes dehydration变成propene.
then propene reacts with HCN(aq)[nucleophilic addition] to form
CH3CH(CN)CH3.
then CH3CH(CN)CH3.undergoes hydrolysis(dilute HCl+reflux)to form 2-methylpropanoic acid.对吗？

dunwan2tellu

alkene 应该不能做nuceophilic addition 吧？(electrophilic addition 才可以）

hvaly

原帖由 dunwan2tellu 于 24-8-2006 07:32 PM 发表
alkene 应该不能做nuceophilic addition 吧？(electrophilic addition 才可以）

对ho,paiseh electrophilic addition才对。谢谢提醒。。。

jayck

energy 的level 会随时改变的,absorb 和release的energy当然也是不定的及不连续的.

hvaly

原帖由 jayck 于 24-8-2006 08:47 PM 发表
energy 的level 会随时改变的,absorb 和release的energy当然也是不定的及不连续的.

paiseh...我还是不是很懂。。。。。
B 有解释到为何有 line spectrum吗？
就算是between 2 energy levels有energy but 如果没有emit出来怎样会有line spectrum呢？C的答案为何不被accept?

jayck

原帖由 hvaly 于 24-8-2006 03:00 PM 发表


D 10 gua

答案是对了
但我不明白为何是10哦..
有谁可解释

24题..我已无法给你更进一步的了解了.不好意思

dunwan2tellu

原帖由 jayck 于 25-8-2006 11:07 AM 发表


答案是对了
但我不明白为何是10哦..
有谁可解释

24题..我已无法给你更进一步的了解了.不好意思

因为你有 5 个 energy level , i.e n=1,2,3,4,5
所以你可以是  n=5-->1 , n=4-->1,n=3-->1,n=2-->1 ,n=5-->2,n=4-->2,n=3-->2,n=5-->3,n=4-->3,n=5-->4

以上是transition of electron from higher energy level to lower energy level 的方法．共有十种

２３题提示：先把 propan-2-ol convert to haloalkane 然后就能用 SN1/SN2 (nuceophilic substitution)加给他一个 C .

[ 本帖最后由 dunwan2tellu 于 25-8-2006 11:18 AM 编辑 ]

jayck

原帖由 dunwan2tellu 于 25-8-2006 11:15 AM 发表


因为你有 5 个 energy level , i.e n=1,2,3,4,5
所以你可以是  n=5-->1 , n=4-->1,n=3-->1,n=2-->1 ,n=5-->2,n=4-->2,n=3-->2,n=5-->3,n=4-->3,n=5-->4

以上是transition ...

好好..谢了.
下一题是什么..
谁提供

dunwan2tellu

问题26

What is the shape of
(i)H2O
(ii) H3O(+)

無聊人

没有人敢尝试galvanic cell的问题吗？

jayck

原帖由 dunwan2tellu 于 25-8-2006 04:06 PM 发表
问题26

What is the shape of
(i)H2O
(ii) H3O(+)

(i)H2O = V-shape
(ii)H3O+ = piramid

问题26
which one of the following has the same number of electron as an alpha     particle?

A. H
B. H+
C. H2
D. He
E. Li+

happytomato

问题26
which one of the following has the same number of electron as an alpha     particle?

A. H
B. H+
C. H2
D. He
E. Li+ [/quote]


B:H+

hvaly

原帖由 jayck 于 26-8-2006 09:19 AM 发表



(i)H2O = V-shape
(ii)H3O+ = piramid

问题26
which one of the following has the same number of electron as an alpha     particle?

A. H
B. H+
C. H2
D. He
E. Li+

question 25
i) V shape
ii) trigonal pyramid


Question 26
答案不是D Helium 吗？

hvaly

Question 27:

Which of the following has the least effect on the retention time of a component?
A relative molecular mass
B density of molecule
C polarity of molecule
D shape of molecule

jayck

原帖由 hvaly 于 26-8-2006 01:27 PM 发表


question 25
i) V shape
ii) trigonal pyramid


Question 26
答案不是D Helium 吗？

错了.
答案是B. H+
alpha particle is a helium necleus,i.e.He2+ and 是没有electron 的.

jayck

会是D吗?
...

hvaly

原帖由 jayck 于 26-8-2006 04:41 PM 发表
会是D吗?
...

答案是B。boiling point和volatility会影响retention time。
如果molecular mass高，higher boiling point, less volatile。
如果molecule是polar的, higher boiling point, less volatile。
如果molecule有branch,lower boiling point,more volatile....
so答案是B。

happytomato

Q28:
The bonding in compound XY tends to be more electrovalent than covalent if

A size of anion Y is small
B size of cation X is small
C charge of cation X is large
D ionisation potentials of X and Y are nearly the same
E X and Y have a small difference in their electronegativity