STPM 化学问题 马拉松！

nikuang04

原帖由 rickykhoo 于 28-8-2007 20:17 发表


对了啦。。
只不过少了一些 steps。。

0.02 mol of compound C is reacted。。
so 0.02 = 0.62/RMS
RMM stands for relative molecular mass。。
RMM = 31
RMM for methanol is 32。。
12 + 3 + 1 ...

答案错了
题目是这样：
When 0.62g of an unknown compound C reacts with PCL5, 0.448 dm3 (measured at stp) of white fumes are evolved and other products are formed.
a)        identify the white fumes.
b)        Identify C (Mr of C=0.62g mol-1, 1 mol of gas occupies 22.4 dm3 at stp)

There are several methods to prepare C. One of those is by using one of the products formed from the above reaction. Suggest the method. Name the mechanism involved.

Based on your knowledge on alkenes, suggest one other method to prepare C. Give the observation.

Relative molecular mass of C 是 62. 0.62g 是 0.62/62=0.01 mol

nikuang04

原帖由 Leong13 于 28-8-2007 20:23 发表
can give some tips

卡帖。。。。。
jiko的想法 diol对了

rickykhoo

原帖由 nikuang04 于 28-8-2007 08:04 PM 发表


答案错了

HAR??
错啊。。

觉得怪怪的。。如果gas evolved occupied 0.302 dm3 的话。。
c 就是 ethanol 咯。。

Leong13

ethane-1,2diol

nikuang04

原帖由 Leong13 于 28-8-2007 20:29 发表
ethane-1,2diol

对了

可以把其他部分都回答吗？

huhuxboy

原帖由 nikuang04 于 27-8-2007 07:02 PM 发表
When 0.62g of an unknown compound C reacts with PCL5, 0.448 dm3 (measured at stp) of white fumes are evolved and other products are formed.
a)        identify the white fumes.
b)        Identify C (Mr of C=0 ...

a) HCl
b) ethane-1,2-diol

product is 1,2-dibromoethane
this compound boiled under reflux with NaOH to form ethane-1,2-diol
nucleophilic substitution

CH2BrCH2Br +  2OH- ---------> CH2(OH)CH2(OH)

from alkene, use ethene.
ethene react with cold dilute  alkaline KMnO4.
decolourisation of purple colour solution and brown ppt is produced

CH2=CH2 + H2O + [O] -------> CH2(OH)CH2(OH)


对吗？？？

huhuxboy

nikuang04 的题目很好。。。
X 灵是名校ho。
我也是槟城的
什么学校应该不重要吧？

[ 本帖最后由 huhuxboy 于 28-8-2007 08:36 PM 编辑 ]

nikuang04

原帖由 huhuxboy 于 28-8-2007 20:30 发表



a) HCl
b) ethane-1,2-diol

product is 1,2-dibromoethane
this compound boiled under reflux with NaOH to form ethane-1,2-diol
nucleophilic substitution

CH2BrCH2Br +  2OH- --------->  ...

你的答案全对
只是product是 1,2-dichloroethane
不是bromine

你好聪明喔

huhuxboy

原帖由 nikuang04 于 28-8-2007 08:32 PM 发表


你的答案全对
只是product是 1,2-dichloroethane
不是bromine

你好聪明喔

不好意思。 想到 bromoethane 去

我忘记很多了。我再翻书看看复习一下。。。

rickykhoo

靠。。考试出浆的题目不就死？！

huhuxboy

这题是我想的题目，我不确定答案，大家来讨论一下。

in esterification between alcohol and carboxylic acid, why we use isotopic labelling using alcohol containing oxygen-18 instead of using carboxylic acid containing oxygen-18 in the -OH group???

rickykhoo

原帖由 huhuxboy 于 28-8-2007 08:42 PM 发表
这题是我想的题目，我不确定答案，大家来讨论一下。

in esterification between alcohol and carboxylic acid, why we use isotopic labelling using alcohol containing oxygen-18 instead of using carbox ...

OH group from carboxylic acid will form water together with the H from alcohol..
thus..isotopic labelling of oxygen-18 is used in alcohol..

[ 本帖最后由 rickykhoo 于 28-8-2007 08:53 PM 编辑 ]

huhuxboy

原帖由 rickykhoo 于 28-8-2007 08:51 PM 发表

OH group from carboxylic acid will form water together with the H from alcohol..
thus..isotopic labelling of oxygen-18 is used in alcohol..

根据你酱说，isotopic labelling of oxygen-18 in -OH group of carboxylic also can use to verify that carboxylic acid undergoes fission of C-O bond and alcohol undergoes fission of O-H bond as oxygen-18 in -OH group of carboxylic acid is found in water.

但是书上大多数都用isotopic labbeling of oxygen-18 in alcohol....

nikuang04

我来解释一下我的题目，以便各位网友能够明白：
Neutralisation occurs between HCl and NaOH to produce NaCl and H2O.
HCl and NaOH --> NaCl + H2O delta H neu = -57KJ mol-1 (不好意思，那个三角形的delta不会放 ）
Base on your knowledge on organic chemistry, suggest a compound that shows the above reaction with NaOH.
Write down the equation.
Will the enthalpy of neutralisation be the same, smaller or greater than the above reaction? explain.

这题其实是老师教phenol的时候想到的。
当时老师说 phenol和NaOH的reaction是exothermic。我就不明白为什么negative
回家想想才知道原来这根本就是Neutralisation，而所有的nertralisation的reaction 都是exothermic的。
答案也可以这样：
C6H5OH + NaOH  C6H5Na + H2O


再来是这题：
When 0.62g of an unknown compound C reacts with PCL5, 0.448 dm3 (measured at stp) of white fumes are evolved and other products are formed.
a)        identify the white fumes.
b)        Identify C (Mr of C=0.62g mol-1, 1 mol of gas occupies 22.4 dm3 at stp)

There are several methods to prepare C. One of those is by using one of the products formed from the above reaction. Suggest the method. Name the mechanism involved.

Based on your knowledge on alkenes, suggest one other method to prepare C. Give the observation.

因为 PCl5是专门用来 test –OH group的。这里算算一下得到0.01mol of C 给了0.02mol of HCl。所以1mol of C会给2mol of HCl
所以C有2个-OH group，就是 diol啦！

算算一下，就知道C是 CH2OH-CH2OH了

而题目的最后一部分答案也可以是 leong 13网友给的加 Br2再hydrolysis
当时我只想到oxidation罢了，所以没有问mechanism。

原帖由 huhuxboy 于 28-8-2007 20:58 发表



根据你酱说，isotopic labelling of oxygen-18 in -OH group of carboxylic also can use to verify that carboxylic acid undergoes fission of C-O bond and alcohol undergoes fission of O-H bond as ...

对啊。所以为什么呢？

rickykhoo

原帖由 huhuxboy 于 28-8-2007 08:58 PM 发表



根据你酱说，isotopic labelling of oxygen-18 in -OH group of carboxylic also can use to verify that carboxylic acid undergoes fission of C-O bond and alcohol undergoes fission of O-H bond as ...

你读什么书？？做什么浆深的？？
有什么答案吗？？
还是其实either alcohol or carboxylic acid used the labelling oxygen will do?
还是因为there are two oxygen atoms in carboxylic acid..so it will be easier if insert oxygen-18 into O-H group in alcohol instead of carboxylic acid?

rickykhoo

原帖由 nikuang04 于 28-8-2007 09:05 PM 发表
因为 PCl5是专门用来 test –OH group的。这里算算一下得到0.01mol of C 给了0.02mol of HCl。所以1mol of C会给2mol of HCl
所以C有2个-OH group，就是 diol啦！

如果在考试时作到这题。。
一开始应该没人想到会是diol吧。。=.="
都是从HCl那边下手。。

jiko

原帖由 nikuang04 于 28-8-2007 09:05 PM 发表
我来解释一下我的题目，以便各位网友能够明白：
Neutralisation occurs between HCl and NaOH to produce NaCl and H2O.
HCl and NaOH --> NaCl + H2O delta H neu = -57KJ mol-1 (不好意思，那个三角形的del ...

方便把那题的calculation放出来吗？？？
我就是算不到。。。
就知道是-diol,没有Mr也算不到什么

nikuang04

原帖由 jiko 于 29-8-2007 14:33 发表


方便把那题的calculation放出来吗？？？
我就是算不到。。。
就知道是-diol,没有Mr也算不到什么

CH2OH-CH2OH加起来不是62么？
怎么算不到？

jiko

原帖由 huhuxboy 于 28-8-2007 08:42 PM 发表
这题是我想的题目，我不确定答案，大家来讨论一下。

in esterification between alcohol and carboxylic acid, why we use isotopic labelling using alcohol containing oxygen-18 instead of using carbox ...

不懂是不是要这样。。。
不是很明白题目

           O                               O
   //            18                 //
R-C        +  R'O   -H  〈======〉 R-C                +  H2O
   \                                \18
    OH                               O-R'
             18
By using the O isotope at alcohol,we can prove that esterification involves breakage of O-H bond at alcohol and C-O at carboxylic .
The ester obtained is found to be radioactive whereas water is not



O-18是放下去用来看alcohol 跟carboxylic acid那个会break -OH 的
如果要知道为什么会这样。。。应该没人懂呱。。
experiment做出来就是这样了。。。。

[ 本帖最后由 jiko 于 29-8-2007 03:06 PM 编辑 ]

jiko

原帖由 nikuang04 于 29-8-2007 02:39 PM 发表


CH2OH-CH2OH加起来不是62么？
怎么算不到？

你给的Mr 不是 0.62 gmol-1吗？？？？
其实是什么来的？？？
我就做不到这个阿

[ 本帖最后由 jiko 于 29-8-2007 03:00 PM 编辑 ]