pantysky 2009-10-16 15:05
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som152 2009-10-16 15:13
goooooooooooooood
fuokho 2009-10-16 15:20
seesee!!!!!!!!!!!!!!!!!!!!!!
k13310 2009-10-16 16:48
good :verygood:
qwert5 2009-10-17 00:17
..............................
~岩石仔~ 2009-10-17 00:34
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footfreak 2009-10-17 00:39
:loveliness: :loveliness: :loveliness: :loveliness: :loveliness:
tommyko0121 2009-10-17 00:42
乙肝臟我們黨內地客戶群眾人
cdl1711 2009-10-17 00:44
thx for sharing:loveliness:
wayne9801 2009-10-17 00:44
let me see it.....thank you
瘋狂楊 2009-10-17 00:45
Thanks for sharing
pakyinhk 2009-10-17 00:48
let me see see sin la
abc169 2009-10-17 01:04
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bobotehao 2009-10-17 01:13
经典好图，看的流口水，thanks
grandpa.ying 2009-10-17 01:26
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tonyewing 2009-10-17 01:27
thank you for your sharing
Photograph 2009-10-17 01:28
Let me see!!!!!!!!!!!!!!!
3962677 2009-10-17 01:30
dddddddddddddddddddddddddddddddddddddddd
asdasdqqqq 2009-10-17 06:18
好誘惑
快來瞧瞧
pefe 2009-10-17 07:30
回復 1# 的帖子
[BeautyLeg] 09年 10月 No. 340 Jill [68 P]
chica5220 2009-10-17 07:56
goodgoodgood
goodgoodgood
x-trek 2009-10-17 08:01
thank you very much
610231 2009-10-17 08:21
thanks for sharing
610231 2009-10-17 08:22
thanks for sharing
snowcat031404 2009-10-17 08:33
Like her leg and also the pose- make me crazy.. :)
peterchan80 2009-10-17 11:07
great gerat let me ccc
kwong623 2009-10-17 11:39
hhhhhhhhhhhhhhhhhhhhhhh
14778520 2009-10-17 11:51
THANKS.........
KFC07 2009-10-17 15:50
:loveliness: :loveliness:
alfredqwe 2009-10-17 15:56
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唔係人 2009-10-17 16:08
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SW 2009-10-17 16:15
不错的主题，值得一看，谢谢
happykwong2006 2009-10-17 16:39
thx for sharing
kit913 2009-10-17 16:45
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KPC 2009-10-17 16:48
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kwan510ts 2009-10-17 17:37
goodgoodgood
撚樣 2009-10-17 17:42
ccccccccccccccccccccc
24557535 2009-10-17 17:46
thanks for sharing
lc0902 2009-10-17 18:02
回復 1# 的帖子
CCCCCCCCCCCCCCCCCCCCCCC
lonebell 2009-10-17 18:45
lllllllllllllllllllll
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5931 2009-10-17 20:10
cccccccccccccccccccccc
crazy123321 2009-10-17 21:54
cccccccccccccccccccccccccccc
pantam 2009-10-17 21:58
goodddddddddddddddddddd
smith100 2009-10-17 22:06
真想看是怎麼樣個舔法 有點噁心 又好像滿好玩的
simon_1l 2009-10-17 22:24
1. Safety precautions:
Safety goggles were worn because methanol solution of 2,4-dinitrtophenylhydrazine and bench dilute sulphuric(VI) acid is corrosive.
The experiment was done away from flame because 2,4-dinitrophenylhydrazine, methanol, ethanol, and many carbonyl compounds are flammable.
2. Sources of error:
The impurities such as pieces of filter paper, excess compound X1, 2,4-dinitrophenylhydrazine might lower the melting point of the derivative. The obtained value might be lower than the value listed in the table given.
3. Suggestions for improvement:
�� The insoluble impurities can be removed by dissolving the solution in ethanol and then being filtered. Then perform recrystallization.
�� The soluble impurities compound X1 and 2,4-dinitrophenylhydrazine might be present in the product before recrystallization. They can be removed in the recrystallization process because of different solubility in ethanol.
4. In selecting a suitable solvent in the recrystallization step, a solvent which the compound X¬ 1 is soluble in when hot and insoluble in when cold should be considered.
5. In the recrystallization procedure, the crystals were dissolved in only the minimum amount of hot ethanol to make the solution achieve saturation so that the yield of product is increased on cooling.
6. If the melting point of the 2,4-dinitrophenylhydrazone is 156℃ we can determine whether the compound X is propanal or pentan-3-one by determining its boiling point.
If the boiling point is 102℃, the compound X should be pentan-3-one;
if the boiling point is 48℃, the compound X should be propanal.
birdbird13 2009-10-17 23:04
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acy823 2009-10-17 23:24
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nickids 2009-10-17 23:39
gggggggggggggggggggg
peter_1234cn 2009-10-17 23:41
good good good....................
spsl2005 2009-10-17 23:45
:loveeyes: :loveeyes: