STPM 化学问题 马拉松！

dunwan2tellu

原帖由 lyt87 于 28-9-2006 10:22 PM 发表
X is phenylmethanol, C:H is nearly 1:1, thus must got aromatic compound.. primary alcohol or any akyl group bonded to benzene ring will be oxidised to benzoic acid

对了！下一题！

lyt87

When compound P, C4H10 O is oxidised, it forms compound Q, C4H8O. Q produces a yellow precipitate when heated with an alkaline iodine solution. the molecular formula of P could be

A  CH3CH2CH2CH2OH
B (CH3)2CHCH2OH
C  CH3CH2CH(OH)CH3
D (CH3)3COH

dunwan2tellu

Answer : C

C4H10O = alcohol
C4H8O = aldehyde / ketone

give positive iodoform test ==> R-CH(OH) or R-C(CH3)O
=> ketone => R-C(CH3)O
=> P = secondary alcohol
=> C) butan-2-ol

dunwan2tellu

问题 50
A coumpound X has composition by mass C 64.88% , H 13.49% , O 21.63% .
2 mole of X reacts with sodium metal to liberate 1 mole of gas hydrogen .
X can be easily oxidised to Y with KMnO4/H+ solution upon heating .
Y can dissociate partially in water .

Identify X .

[ 本帖最后由 dunwan2tellu 于 29-9-2006 10:38 AM 编辑 ]

C011201

C : 64.88/12 = 5.4
H : 13.49/1  = 13.49
O : 21.63/16 = 1.35

C:H:O = 4:10:1

X; C4H10O ==>  alcohol

2 mole of X react with Na in ether to produce 1 mole of hidrogen
1 mole of X react with Na in ather to produce 1/2 mole of hydrogen
==> there is one -OH group in X.

X can be easily oxidised to Y with KMnO4/H+ solution upon heating .
Y can dissociate partially in water
Primary alcohol can be oxidised to carboxylic acid easily. carboxylic acid dissociate partially in water. X is an primary alcohol.

X: C4H9OH

对吗？

C011201

Which of the following can be use to differentiate between athylamine and ethanamide ?

1 hot and dilute sodium hydroxide
2 cold and dilute hydrochloric acid
3 ethanoyl chloride

dunwan2tellu

原帖由 C011201 于 29-9-2006 03:51 PM 发表
Which of the following can be use to differentiate between ethylamine and ethanamide ?

1 hot and dilute sodium hydroxide
2 cold and dilute hydrochloric acid
3 ethanoyl chloride

1,2,3

ethanamide is primary amide , so it can undergo hydrolysis with hot , dilute NaOH to give off ammonia gas(this is the confirmation test for primary amide also) ,whereas amine wont undergo hydrolysis with NaOH.
CH3CONH2 + NaOH(aq) --> NH3 + CH3COONa

ethlyamine can undergo neutralisation with cold and dilute hydrochloric acid , so it dissovle in dilute HCl to form salt and water whereas ethanamide cannot undergo neutralisation .

CH3CH2NH2 + HCl(aq) --> CH3CH2NH3(+) Cl(-)  

ethylamine can react vigorously with ethanoyl chloride to give white solid , N-ethylethanamide

2CH3CH2NH2 + CH3COCl --> CH3CH2NH3Cl + CH3CONHCH2CH3

CH3CH2NH3Cl is formed when HCl produced during the reaction react with excess ethylamine .
amide does not react with ethnoyl chloride.

[ 本帖最后由 dunwan2tellu 于 2-10-2006 11:42 AM 编辑 ]

dunwan2tellu

问题 52 (STPM pass year 2002)
In the reaction :

Cu(2+) + 4NH3 -->[Cu(NH3)4](2+)

the Cu(2+) ion acts as a

A.Lewis acid
B.Lewis base
C.Bronsted-Lowry acid
D.Bronsted-Lowry base

C011201

A Lewis Acid

Cu(2+) has empty d orbitals. Cu(2+) can receive electron pairs from NH3 to form dative bond

dunwan2tellu

原帖由 C011201 于 2-10-2006 12:54 PM 发表
A Lewis Acid

Cu(2+) has empty d orbitals. Cu(2+) can receive electron pairs from NH3 to form dative bond

答对！下一题！

C011201

Chlorine reatcs with all the compounds listed below. In which case is the mole reacting ratio between chlorine and the said reagent the highest?

A cold aqueous sodium hydroxide
B hot aqueous sodium hydroxide
C aqueous potassim iodide
D dry ammonia

[ 本帖最后由 C011201 于 3-10-2006 06:58 AM 编辑 ]

dunwan2tellu

Chlorine reatcs with all the compounds listed below. In which case is the mole reacting ratio between chlorine and the said reagent the highest?

A cold aqueous sodium hydroxide
B hot aqueous sodium hydroxide
C aqueous potassim iodide
D dry ammonia

A : Cl2 + 2NaOH --> NaClO + NaCl + H2O
B : 3Cl2 + 6NaoH -->NaClO3 + 5NaCl+3H2O
C : 2KI + Cl2 -->2KCl + I2
D : Cl2 + 2NH3 --> NH4Cl + NH2Cl ????

A,B,C 的 ratio 都一样，我猜是 D 不过不知道是什么reaction 哈哈。

C011201

对了， 不过是这样：
3Cl2 + NH3 --> NCl3 + 3HCl
ratio 1:3

dunwan2tellu

原帖由 C011201 于 3-10-2006 11:40 PM 发表
对了， 不过是这样：
3Cl2 + NH3 --> NCl3 + 3HCl
ratio 1:3

怎么那么陌生

问题 54

Explain why all group 14 tetrachloride undergoes hydrolysis except CCl4 ?

ronloh94

原帖由 dunwan2tellu 于 4-10-2006 11:39 AM 发表




问题 54

Explain why all group 14 tetrachloride undergoes hydrolysis except CCl4 ?

During hydrolysis of group 14 tetrachloride, the atoms of silicon, germanium, tin and lead make use of the empty d-orbital in their valence shells to form dative bonds with water molecules.
Carbon is an period 2 element, does not have empty 2-d orbital in its valence shell. It cannot expand its valancy to form dative bonds with water molecules. Hence, CCl4 cannot be hydrolysed.

ronloh94

How many isomers are there for an acyl chloride with the molecular formula of C5H9OCl?

A 3
B 4
C 5
D 6

ronloh94

How many isomers are there for an acyl chloride with the molecular formula of C5H9OCl?

A 3
B 4
C 5
D 6

dunwan2tellu

How many isomers are there for an acyl chloride with the molecular formula of C5H9OCl?

A 3
B 4
C 5
D 6

Answer B
CH3CH2CH2CH2COCl
CH3CH(CH3)CH2COCl
CH3CH2CH(CH3)COCl
CH3C(CH3)2COCl

dunwan2tellu

问题 56
Which property of the group 2 elements(Mg -> Ba) or their compounds increase with increasing proton number ?

A.Stability of the carbonate when heat
B.magnitude of the enthalphy change of hydration of the metallic ion
C.standard electrode potential of group 2 metal
D.acidity of an aqueous solution of its chloride .

ronloh94

原帖由 dunwan2tellu 于 4-10-2006 06:16 PM 发表

Answer B
CH3CH2CH2CH2COCl
CH3CH(CH3)CH2COCl
CH3CH2CH(CH3)COCl
CH3C(CH3)2COCl

你中骗了~ 答案是 C 5

因为
CH3CH2CH2CH2COCl  (1个)
CH3CH(CH3)CH2COCl   (1个)
CH3C(CH3)2COCl  (1个)
CH3CH2C*H(CH3)COCl《—有一个chiral carbon,所以有optical isomer(2个)                                                                        

所以总共有五个isomer.