STPM 化学问题 马拉松！

vloh8

小弟有一题不会，还请大家赐教。               (STPM 03 P1 Q39)

when 1 mol of compound X is heated with a concentrated solution
of potassium manganate 7 2 mol of compound Y with the molecular formula C2H4O2 is
produced.Compund X undergoes polymerisation in the presence of Al(CH3)3 to form compund Z.
The structure of Z could be ?


ANS:
-(CH(CH3)-CH2-CH(CH3)-CH2-CH(CH3))-


为何答案不是

-(CH(CH3)-CH(CH3)-CH(CH3)-CH(CH3)-CH(CH3))-

dunwan2tellu

X 应该是 but-2-ene CH(CH3)=CH(CH3) ,这样的话 oxidation + heat 就会给你 2 个 carboxylic acid(也就是 ethanoic acid) . X undergoes polymerisation with Ziegler-Natta catalyst

然后 form -(CH(CH3)-CH(CH3)-CH(CH3)-CH(CH3)-CH(CH3))-

我觉得可能答案有错吧？

[ 本帖最后由 dunwan2tellu 于 17-11-2006 09:26 AM 编辑 ]

ronloh94

原帖由 lowch1 于 15-11-2006 01:06 PM 发表


搞错。。。连我的名都打错。。。



Aliphatic carboxylic acid 好象有 Dark Red colour ....

能不能解释一下为什么有Dark Red colour?和Fe(3+)原本的颜色不同吗？谢谢。

dunwan2tellu

原帖由 ronloh94 于 17-11-2006 09:16 AM 发表

能不能解释一下为什么有Dark Red colour?和Fe(3+)原本的颜色不同吗？谢谢。

我的老师说 FeCl3 在 STPM 里只是用在organic 里来 test for phenol (有phenol就会有 purple colour complex) .至于其他的，他说  out of syllybus .

问题 83
Explain the following observation :
(i)Across the period from left to right, the property of oxide changes from basic oxide to acidic oxide .

(ii)Going down the group ,the property of oxide changes from acidic oxide to basic oxide

为什么没有人回答我的问题的

ronloh94

Tan Yin Toon的 Fajar Bakti 第462页有提到咧。
如果不用这个，用什么方法分辨benzoic acid and aliphatic carboxylic acid?

ronloh94

原帖由 dunwan2tellu 于 17-11-2006 08:59 AM 发表
X 应该是 but-2-ene CH(CH3)=CH(CH3) ,这样的话 oxidation + heat 就会给你 2 个 carboxylic acid(也就是 ethanoic acid) . X undergoes polymerisation with Ziegler-Natta catalyst

然后 form -(CH(CH3)-CH ...

我也觉得答案错。这本6-year series答案蛮多错的。
你看它的解释说答案是 -[-CH(CH3)-CH(CH3)-]- ,却说答案是B.
B 明明是-[-CH(CH3)-CH2-]-  

再见是为了明天

Which of the following oxides has a molecular structure as distinct from a giant structure ?

A.Na2O    B.MgO    C.SiO2   D.Cl2O7

lewisham

c silicon (iv)oxide exist as giant molecular

Faiz

C.SiO2....

keejoyce

hai...help me solve,,,   the concentration of silver ion Ag+ in a saturated solution of silver ethanedioat,Ag2C2O4 at 298 K is 2.3*10^-4 moldm-3.wat is solubility product of silver ethanedioat at same temp.
A.2.6*10^-8
B.5.3*10^-8
C.6.1*10^-12
D.1.2*10^-11

morphv02c01

原帖由 keejoyce 于 30/5/07 12:54 AM 发表
hai...help me solve,,,   the concentration of silver ion Ag+ in a saturated solution of silver ethanedioat,Ag2C2O4 at 298 K is 2.3*10^-4 moldm-3.wat is solubility product of silver ethanedioat at ...

应该是D吧？

morphv02c01

原帖由 dunwan2tellu 于 14/11/06 10:12 AM 发表
NH4OH 我上网查，看到 http://www.chem.uiuc.edu/webFunChem/bases/base6.htm . 我想它是存在的。

下一题

问题 83
Explain the following observation :
(i)Across the period from left to right, the ...

Erm, we relate basic properties to ionic, and acidic properties to covalent.
Across the period, screnning effect remains constant, therefore effective nuclear charge increases and the outermost shell of electrones are pulled nearer to the nucleus, as so the polarising power of the cation increases from left to right. Therefore the oxides changes from basic to acidic across the period.

Down a group, screening effect outweights the effective nuclear charge as electrones are added to the inner shell. Hence the attraction towards electrons decreases. When this happens the compound formed will be possesing more ionic character as the electron cloud of the anion is not distorted and causing overlap of the valance shell to form covalent bond. Therefore the oxides changes from acidic to basic down a group.

再见是为了明天

原帖由 keejoyce 于 30-5-2007 12:54 AM 发表
hai...help me solve,,,   the concentration of silver ion Ag+ in a saturated solution of silver ethanedioat,Ag2C2O4 at 298 K is 2.3*10^-4 moldm-3.wat is solubility product of silver ethanedioat at ...

Ag2CrO4 <===> 2Ag+ + (CrO4)^2-

Ksp Ag2CrO4 = [Ag+]^2 * [CrO4]
            = (2.3*10^-4)^2 * ((2.3*10^-4)/2)
            = 6.xx *10^-12

keejoyce

原帖由 morphv02c01 于 30-5-2007 12:42 PM 发表



应该是D吧？

answer is C

morphv02c01

原帖由 keejoyce 于 30/5/07 08:01 PM 发表


answer is C

哦，sorry sorry。。你楼上的对了。。hehe。。

再见是为了明天

0.05mol sodium benzoate(C6H5COONa) was dissolved in water in a 100cm^3 volumetric flask .What is the pH of the aqueous solution formed ?
[Ka for C6H5COOH is 6.5x10^-5 moldm^-3] ,[Kw of water is 1x10^-14mol^2 dm^-3]

A 8.9
B 8.4
C 3.9
D 2.9

huhuxboy

答案是 A

对吗？

[ 本帖最后由 huhuxboy 于 1-6-2007 09:48 PM 编辑 ]

huhuxboy

C6H5COONa dissociate completely in water to form C6H5COO- and Na+ ions.

C6H5COO- + H2O <==> C6H5COOH + OH-
Let the base dissociation constant of this reaction be Kb

C6H5COO- is almost equal to 0.5M as the equilibrium lies to the left

Ka x Kb = Kw

6.5x10^-5 x [OH-]^2 / 0.5 = 1x10^-14

[OH-] = 8.77 x 10^-6 M
pOH = - log 8.77x10^-6
        =5.06
pH= 14 - pOH
pH=14-5.06
pH=8.9

[ 本帖最后由 huhuxboy 于 1-6-2007 09:55 PM 编辑 ]

huhuxboy

The addition of NO2 to a mixture of methane and chlorine i the presence of light at temperature 140'C decreases the rate of the chlorination of methane. Which of the following statement correctly explains the above observation.?

A. NO2 reduces the number of chlorine radicals.
B. NO2 prevents the formation of the chlorine radicals.
C. NO2 prevents the collision of the chlorine radicals with the methane molecules.
D. NO2 breaks the C-H bond in methane.

E^e

A...........