STPM 化学问题 马拉松！

UnitedDream

原帖由 hvaly 于 18-9-2006 10:39 AM 发表


是不是因为germanium compound has a higher bond energy than the bond energy between atoms of germanium(catenation compound)?so it tends to form compound of germanium than catenation compound??

对了 。 The only element that form stable catenation compound in group 14 is carbon . this is because carbon-carbon bond is very strong .While Si , Ge , Sn , Pb , the bond energy between is own element is low .

对不起咯 ， dunwan2tellu  ，

我会很小心出题的

dunwan2tellu

问题44

Aluminium oxide is insoluble in water but is soluble in both dilute acid and concentrated alkaline . Which of the following best explain this observation ?

A.Aluminium oxide is amphoteric
B.The bond in aluminium oxide is partially ionic and partially covalent
C.Aluminium oxide  is an ionic compound
D.The lattice energy of aluminium oxide is high

QooLuo

原帖由 dunwan2tellu 于 23-9-2006 09:23 AM 发表
问题44

Aluminium oxide is insoluble in water but is soluble in both dilute acid and concentrated alkaline . Which of the following best explain this observation ?

A.Aluminium oxide is amphote ...

是B吗?

Shinrei

答案是A

dunwan2tellu

答案是 B (pass year) 来的。
Qoo Luo 可以放下一题。

QooLuo

The following observation were made when a compound X was reacted with the respective reagents.
(i) Forms a yellow precipitate with alkaline iodine solution.
(ii) Is oxidised to a carboxylic acid by acidified potassium manganate(VII)
(iii) Does not produce hydrogen gas when reacted with sodium.
Compound X may be
A. CH3CH2CHOHCH3
B. (CH3)3COH
C. CH3CH2CHO
d. C6H5COCH3

dunwan2tellu

The following observation were made when a compound X was reacted with the respective reagents.
(i) Forms a yellow precipitate with alkaline iodine solution.
(ii) Is oxidised to a carboxylic acid by acidified potassium manganate(VII)
(iii) Does not produce hydrogen gas when reacted with sodium.
Compound X may be
A. CH3CH2CHOHCH3
B. (CH3)3COH
C. CH3CH2CHO
d. C6H5COCH3

(i) 表示 give positive iodoform test ，所以有 R-CH(OH)(CH3) 或 R-COCH3
(ii)可以做 oxidation
(iii)没有 OH group

我觉得答案是 D
A,B 肯定错，因为有 OH group . C 则不能 give positive iodoform test.剩下 D. 不过 D 是 ketone ,所以一定要 reflux 才能成为 carboxylic acid .

[ 本帖最后由 dunwan2tellu 于 24-9-2006 07:50 PM 编辑 ]

dunwan2tellu

问题 46
Which of the following compounds , is fastest to form a precipitate with an aqueous solution of argentum nitrate ?

A.CH3CH2CH2Cl
B.CH3CCl3
C.CH3COCl
D.ClCH2COOH

lyt87

是C吗？？？？？？？？

dunwan2tellu

原帖由 lyt87 于 24-9-2006 10:01 PM 发表
是C吗？？？？？？？？

lyt87 阔别那么旧，又回来啦？对了就是 C 因为 alcyl chloride is very reactive compare to haloalkane and others .请放下一题。

lyt87

The same carboxylic acid is obtained either by hydrolysis of a nitrile X or by oxidation of alcohol Y. Which pair could be X and Y?
             X                    Y
A.        CH3CH2CN            CH3CHOH
B.        C6H5CH2CN           C6H5CH2CH2OH
C.        C6H5CH2CN           C6H5CH2OH
D.       (CH3)2CHCN           (CH3)3COH

UnitedDream

原帖由 dunwan2tellu 于 24-9-2006 07:47 PM 发表

(i) 表示 give positive iodoform test ，所以有 R-CH(OH)(CH3) 或 R-COCH3
(ii)可以做 oxidation
(iii)没有 OH group

我觉得答案是 D
A,B 肯定错，因为有 OH group . C 则不能 give positive iodoform ...

D 虽然是ketone， 但它attach to a phenyl group , 所以照normal的oxidation condition 就可以oxidise 它

QooLuo

原帖由 dunwan2tellu 于 24-9-2006 07:47 PM 发表

(i) 表示 give positive iodoform test ，所以有 R-CH(OH)(CH3) 或 R-COCH3
(ii)可以做 oxidation
(iii)没有 OH group

我觉得答案是 D
A,B 肯定错，因为有 OH group . C 则不能 give positive iodoform ...

对了，答案是D.

mingann

explain:
1)magnesium chloride is much soluble in water than barium sulphate

2)beryllium oxide is amphoteric but magnesium oxide is ionic

3)magnesium chloride and aluminium chloride differ in volatility

4)why boiling point of oxygen(-183C) is higher than nitrogen(-196C)

谢谢回答。。我真的很需要这些答案。。。

dunwan2tellu

1)magnesium chloride is much soluble in water than barium sulphate

solubility 是看 hydration energy - lattice energy
MgCl2 因为 product of charge < BaSO4 ,所以 MgCl lattice energy lower , 所以 solubility higher

2)beryllium oxide is amphoteric but magnesium oxide is ionic

beryllium oxide is high charge density at beryllium ion , 所以 form amphoteric

3)magnesium chloride and aluminium chloride differ in volatility

volatility 看 boiling point .MgCl 是 strong ionic bond , 所以 boiling point higher .AlCl3 has intermolecular weak van der waals force(due to high charge density at Al(3+)) , so it has lower boiling point

4)why boiling point of oxygen(-183C) is higher than nitrogen(-196C)

both are bonded by weak intermolecular van der waals force . Bigger the molecule size , stronger the force .Size of oxygen > size of nitrogen(因为 porton no increase,attraction between nucleus and electron valens become stronger)

UnitedDream

补充一下this is due to diagonal relationship . Li will have similiar chemical properties as Mg , Be and Al

UnitedDream

原帖由 mingann 于 25-9-2006 08:59 PM 发表
explain:
3)magnesium chloride and aluminium chloride differ in ...

补充一下
Magnesium chloride is ionic compound , therefore it's ions is held by strong ionic bond in giant ionic lattice while aluminium chloride is simple covelent molecule with covelent bond with ionic characterisic between it's atoms due to high charge density of Al3+ and weak van der walls force between it's molecule .

[ 本帖最后由 UnitedDream 于 26-9-2006 07:03 PM 编辑 ]

snowball

原帖由 dunwan2tellu 于 12-9-2006 07:14 AM 发表


正确的答案是 (ii) > (iii) > (i)

因为 NO2 is electron withdrawing group ,when bonded to benzoic acid will make it more stable .Equilibirum will shift to right causing more proton to be  ...

(i) 2-phenyl-benzoic acid
(ii)2-nitro-benzoic acid
(iii)benzoic acid

应该是 (ii)>(i)>(iii) 吧？

(ii) has the highest strength of acidity because NO2 is electron withdrawing groups.
(iii) stronger strength than (i) because it got phenyl group which is electron withdrawing groups than Benzoic acid?

dunwan2tellu

(i) 2-phenyl-benzoic acid
(ii)2-nitro-benzoic acid
(iii)benzoic acid

应该是 (ii)>(i)>(iii) 吧？

(ii) has the highest strength of acidity because NO2 is electron withdrawing groups.
(iii) stronger strength than (i) because it got phenyl group which is electron withdrawing groups than Benzoic acid?

我在 #131 已经解释是我疏忽，打错了。

The same carboxylic acid is obtained either by hydrolysis of a nitrile X or by oxidation of alcohol Y. Which pair could be X and Y?
             X                    Y
A.        CH3CH2CN            CH3CHOH
B.        C6H5CH2CN           C6H5CH2CH2OH
C.        C6H5CH2CN           C6H5CH2OH
D.       (CH3)2CHCN           (CH3)3COH

B  C6H5CH2CN   hydrolysis 成为 C6H5COOH
C6H5CH2CH2OH oxidatize to C6H5COOH

其他的都不会得到同样的 product.

问题 48
C7H8O , on heating with acidic solution potassium manganate(VII) , gives X with formula C7H6O2 . Identify X .

lyt87

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