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Dicardo

1. The lattice enery of NaF and NaCl are -981 kJ mol and -780 kJ mol respectively. Which of the following statement explain the diffrence between the lattice energu of the 2 compound?
A. Fluorine is more electronegative than clorine
B. NaF is more stable than NaCl
C. The charge density of the fluoride ion is higher than that of chloride ion.
D. NaF is more stable than NaCl.

2. In which of the following liquids the particle are held together by weak Van de Waals force?
A. water
B. silver
C. Sodium Chloride
D. silicon dioxide

3. A mixture of N2O4 and NO2 at 323K and 101kPa has a molar mass of 60.0 gmol^. Calculate the Kc for it when it is in equilibrium.
A. 1.6 X10^5 Pa
B. 3.6 X10^5 Pa
C. 5.7 X10^4 Pa
D. 1.2 X10^4 Pa

4. In the anodisation of aluminium,
A. the aluminij object is made an anode of the electrolytic cell
B. oxygen gas is bubble into the cell to oxidese the aluminiu object
C. the electrolyte used is dilute chromic acid
D. a current of about 40000A is used to keep the cell at 900"C

5. Which if the following statements regarding dinitrogen tetraoxide and nitrogen dioxide is true ?
A. N2O4 is yellowish and NO2 is reddish-brown
B. NO2 is an electron deficient molecule
C. N2O4 molecule has two sigma and two pi bond
D. The hybridisation of the nitrogen atom in NO2 molecule is sp3.

6. Chromium III ion forms a complex with ligand L. It was found that a 5.0cm3 of 0.05M aqueous chromium III sulphate reacts with exactly 15.0 cm3 of 0.05M aqueous solution of ligand L. L could be
A. C2O4 (2-)
B. EDTA (4-)
C. H2NCH2CH2NHCH2CH2NH2
D. F (-)

7. Which sequence of the compound according to the ascending order of thier reactivity towards nucleophilic substitution, is correct?
1 - CH3CH2CH2CH2C
2 - CH3COCl
3 - C6H5Cl
A. 1-2-3
B. 3-2-1
C. 2-1-3
D. 3-1-2


帮帮忙。。。

书里的答案是：
1-C  2-D  3-A  4-C  5-B  6-A  7-D

游戏女王

答案都给了你还要问什么 ？

Dicardo

原帖由 游戏女王 于 4-12-2009 01:50 PM 发表
答案都给了你还要问什么 ？

都是不明白。。。希望有人可以解释。。

游戏女王

第一题是group １７的问题 。。。
第二题 water 是 hydrogen bond ，silver 又没有给molecule ，应该是atom ，NaCl 是ionic bond ，所以是silicon dioxide SiO２ ...

Dicardo

原帖由 游戏女王 于 4-12-2009 01:57 PM 发表
第一题是group １７的问题 。。。
第二题 water 是 hydrogen bond ，silver 又没有给molecule ，应该是atom ，NaCl 是ionic bond ，所以是silicon dioxide SiO２ ...

isnt water got Hydrogen bonb and V.dW force ?

游戏女王

water = 2 atom hydrogen and one atom of oxygen .....
ur question is water oni ... u oni care about the h2o molecule ..
hydrogen bond bind two hydrogen one oxygen together ...
and ...
van der waals force actually is exist in all molecules ..
but since ur question ask van der waals force , the posible answer is oni SiO2 ...

游戏女王

其他的不懂啦 。。

四月一日的小皮

4.answer should be a & c,anode is aluminium object,so that it can react with oxygen.chromic acid=acidifed dicromate acid,H2Cr2O7,which give out oxygen.
5.nitrogen in NO2 got 2 bonding pair but with 1 unpaired electron.
6.FIND RATIO OF MOLE BETWEEN THIS TWO MIXTURE.
  2.5x10^-4:7.5x10^-4= 1:3,which mean 1 chromium (iii) ion form complex ion  
   with 3 ligands molecules.
7.you can refer tis page...
   http://www.recom.org/forum/showthread.php?t=7922&page=43

[ 本帖最后由 四月一日的小皮 于 4-12-2009 07:28 PM 编辑 ]

Dicardo

5. >> why NO2 is an electron deficient molecule ?
               
                   O
                   ||
                 . N --> O

isnt NO2 is like this ?
there is an electron which is unpair.. so it should not be electron deficient, right ?

夜神锋

no1
we need to compare the energy released,
the lattice energy of NaF is higher than NaCl

lattice energy is depends on the charge and the atomic radius, since the charge is same, -1,so we look on the atomic radius.the smaller atomic radius the higher lattice energy,the atomic radius of fluorine is smaller than chlorine,and also we know the smaller the size, the higher the charge density,
so we can infer that the charge density of F- ion is higher than Cl- ion

lawrenceleong88

楼主目前还不明白哪一题呢？
原来和大学预科班的课程几乎相同。。。可能他们也能帮到你的。。。

四月一日的小皮

原帖由 Dicardo 于 4-12-2009 03:15 PM 发表
5. >> why NO2 is an electron deficient molecule ?
               
                   O
                   ||
                 . N --> O

isnt NO2 is like this ?
there is an electron which is u ...

nitrogen atom in the NO2 only have 5 electron,which mean it lack 3 electron to have stable octet configuration.it is known as electron-deficient molecules.

idontwant2b

7. chlorobenzene有aromatic group close to chlorine, render it hard to undergo nucleophilic substitution,
so must be least reactive among the 3.

acyl chloride is very reactive due to chlorine, a good leaving group attached to a group easily attacked by incoming species.

meiling

1.lattice energy的改变是可以用formula来看的
lattice energy is directly proportional to the product of charge and inverly proportional to the product of the radius，那么charge over radius就是charge density了，所以答案就跟charge density有关系。那么两个的cation都一样的，所以就是看anion，fluorine比较小粒，charge又跟chlorine一样，所以NaF的charge density比较高

2. In which of the following liquids the particle are held together by weak Van de Waals force?
A. water（hydrogen bond）
B. silver（strong metallic bond）
C. Sodium Chloride（electrostatic force）
D. silicon dioxide（weak van de waals force）

3. A mixture of N2O4 and NO2 at 323K and 101kPa has a molar mass of 60.0 gmol^. Calculate the Kc for it when it is in equilibrium.
A. 1.6 X10^5 Pa
B. 3.6 X10^5 Pa
C. 5.7 X10^4 Pa
D. 1.2 X10^4 Pa

这题我不理解，给的molar mass不是N2O4 也不是 NO2的，问Kc却要我们给Kp

4. In the anodisation of aluminium,
A. the aluminium object is made an anode of the electrolytic cell
B. oxygen gas is bubble into the cell to oxidese the aluminiu object
C. the electrolyte used is dilute chromic acid
D. a current of about 40000A is used to keep the cell at 900"C

其实这题A和C都对，没得解释，自己读nota然后背起来

5. Which if the following statements regarding dinitrogen tetraoxide and nitrogen dioxide is true ?
A. N2O4 is yellowish and NO2 is reddish-brown
（Pure N2O4 is colourless, N2O4 seems to be yellowish in nature because it will dissociate into NO2 which is brown until it reach equilibium. ）
B. NO2 is an electron deficient molecule
（very clear, N only hav 7 electrons surrounding it, it has only 1 electron in it's lone pair, tat's why it can form N2O4）
C. N2O4 molecule has two sigma and two pi bond
（it has 5 sigma, 2 pi bond. Wan to know y? just draw the structure）
D. The hybridisation of the nitrogen atom in NO2 molecule is sp3.（it is sp only）

6. Chromium III ion forms a complex with ligand L. It was found that a 5.0cm3 of 0.05M aqueous chromium III sulphate reacts with exactly 15.0 cm3 of 0.05M aqueous solution of ligand L. L could be
A. C2O4 (2-)
B. EDTA (4-)
C. H2NCH2CH2NHCH2CH2NH2
D. F (-)

（transition metal我还没读^^）
7. Which sequence of the compound according to the ascending order of thier reactivity towards nucleophilic substitution, is correct?
1 - CH3CH2CH2CH2C（it's normal, firstly do not bother about it）
2 - CH3COCl（it is known that acyl chloride is a very reactive compaund, so it must be the most reactive）
3 - C6H5Cl（something of chlorine will delocalise in to the ring, so the bond between Cl and the benzene is apparently a double bond, the bond length is shorter then a single bond but longer then a double bond, so it is the strongest 1）
from all the explanation above, we know the reactivity increase from 3-1-2

我都后面懒惰了，全部用英文了

Dicardo

大概动了。。
原来我一直误解NO2 electron deficeint的意思...

idontwant2b

你好像从longman 6 years series那边看来的是吗？
其实那本书很多错误的。

Dicardo

没参考书..

idontwant2b

那祝你好运了！

p/s: longman那本历年考题的书错误蛮多的，

Dicardo

我用oxford fajar 那本可可色的。。。