STPM化学专区

Dicardo

原帖由 idontwant2b 于 24-11-2009 11:51 AM 发表


heating ammonium salt with strong base yields ammonia

2NH4Cl+ Ca(OH)2 -> 2NH3 + CaCl2 + 2H2O
虽然我也是错…紧张过度。

嘻嘻。。我对。。。
可是前面两题我不会。。。

idontwant2b

前面三题有谁要分享答案吗?

1. gas X:? explanation?
Line of Lower pressure?
line of negative deviation, reason?

2. deviation?
what is azeotrope?
45% ethanol - vapour composition of distillate and azeotrope

大概是这样。

2.

Dicardo

原帖由 idontwant2b 于 24-11-2009 11:56 AM 发表
前面三题有谁要分享答案吗?

1. gas X:? explanation? H2 , smallest mass and volume, can be ignore, nearly ideal
Line of Lower pressure? line with a smaller gradient
line of negative deviation, reason? volume cannot be ignore.

2. deviation? positive
what is azeotrope? :@
45% ethanol - vapour composition of distillat ...

this is what i wrote..

darksider

原帖由 idontwant2b 于 2009/11/24 11:26 AM 发表
第一题很奇怪…
什么意思？第三题a i 为什么bonus?

后面essay题蛮不错的。

Ca(OH)2(s)+NH4Cl(s)>CaCl2(s)+2NH3(g)+2H2O(l)
书里的。。幸好只是一分。

idontwant2b

原帖由 Dicardo 于 24-11-2009 12:03 PM 发表


this is what i wrote..

觉得能至少Ｂ－，
我对ｅｓｓａｙ比较有信心。

Dicardo

原帖由 idontwant2b 于 24-11-2009 12:08 PM 发表


觉得能至少Ｂ－，
我对ｅｓｓａｙ比较有信心。

我要A的！！！！:@

darksider

原帖由 idontwant2b 于 2009/11/24 11:56 AM 发表
前面三题有谁要分享答案吗?

1. gas X:? explanation?
Line of Lower pressure?
line of negative deviation, reason?

2. deviation?
what is azeotrope?
45% ethanol - vapour composition of distillat ...

Azeotrope is a mixture that has a constant boiling point and a fixed composition.

Vapour composition of after mixture containing 45% ethanol undergoes 2 fractional distillation is 83% ethanol and17% water.

Azeotropic 1 is 9x% ethanol and 100-9x% water.

positive deviation becuz the azeotrope has the lowest b.p

1) PV = nRT ; nRT kept constant , P decreases so V must increases. The line for gas X at pressure P' (P'<P) is above the line for gas X at pressure P.

gas Y shows negative deviation ; therefore it has occupies lower volume than X at 0 degree celcius ; reason : intermolecular forces operate between molecules of gas Y.

[ 本帖最后由 darksider 于 24-11-2009 12:17 PM 编辑 ]

Dicardo

原帖由 darksider 于 24-11-2009 12:12 PM 发表


Azeotrope is a mixture that has a constant boiling point and a fixed composition.

Vapour composition of after mixture containing 45% ethanol undergoes 2 fractional distillation is 83% ethanol a ...

.....
这整题我好像只拿 3 分。。

idontwant2b

我５ａ　ｉ　错了，没有ｋｅｙ　ｗｏｒｄ　＂against the attractive force＂
5b (ii)
6b (ii)
7a
9b(iii) (iv)
10a (ii)
b(iii)
谁要分享答案吗？

darksider

原帖由 idontwant2b 于 2009/11/24 12:20 PM 发表
我５ａ　ｉ　错了，没有ｋｅｙ　ｗｏｒｄ　＂against the attractive force＂
5b (ii)
6b (ii)
7a
9b(iii) (iv)
10a (ii)
b(iii)
谁要分享答案吗？

5b(ii) KBr is thermally stable. (just predict, no need explain ; if need , then it is due to strong ionic bonds)

6b(ii) According the Arrhenius equation , k = Ae^(-Ea/RT) , when temperature increases, k decreases and in this case, k for both forward and backward reaction increases. Therefore, rate of attainment of the equilibrium will increase as temperature increase.

9b(iii) 2,3,4-trimethylhexane ; the shorter the chain, the higher the octane number
9b(iv) to produce shorter chains of alkanes ; to produce useful alkenes [ not sure if it's correct]

10a (ii)test for phenolic group ; add Na(s) at room temperature to a solution of dopamine, if effervescence of gas/hydrogen gas which produces pop sound in lighted wooded splinter, then it means that dopamine has phenolic group. Write out the rxn equation

test for amino group ; add dopamine to a solution containing nitrous acid which is prepared in-situ by adding NaNO2 and HCl at room t. If N2 gas is evolved, it means that dopamine has an amino group .

10b(iii) because it softens on heating and hardens on cooling.

[ 本帖最后由 darksider 于 24-11-2009 12:33 PM 编辑 ]

idontwant2b

原帖由 darksider 于 24-11-2009 12:31 PM 发表


5b(ii) KBr is thermally stable. (just predict, no need explain ; if need , then it is due to strong ionic bonds)

6b(ii) According the Arrhenius equation , k = Ae^(-Ea/RT) , when temperature inc ...

ｆｏｒ　ｅｔｈａｎｏｌｉｃ　ｇｒｏｕｐ，ａｄｄ　ＦｅＣｌ３　可以吗？

darksider

原帖由 idontwant2b 于 2009/11/24 12:36 PM 发表


ｆｏｒ　ｅｔｈａｎｏｌｉｃ　ｇｒｏｕｐ，ａｄｄ　ＦｅＣｌ３　可以吗？

不是很懂因为dopamine有两个OH groups.
我记得如果用FeCl3的话，

FeCl3 + C6H5OH ------> (C6H5)3Fe + 3HCl
----------------------------------purple complex

idontwant2b

原帖由 darksider 于 24-11-2009 12:39 PM 发表


不是很懂因为dopamine有两个OH groups.
我记得如果用FeCl3的话，

FeCl3 + C6H5OH ------> (C6H5)3Fe + 3HCl
----------------------------------purple complex

好多错误…
拿ａ／ａ－的希望没了…

发现这次很少ｃａｌｃｕｌａｔｉｏｎ…
第六题大家拿到什么答案？

darksider

原帖由 idontwant2b 于 2009/11/24 12:43 PM 发表


好多错误…
拿ａ／ａ－的希望没了…

发现这次很少ｃａｌｃｕｌａｔｉｏｎ…
第六题大家拿到什么答案？

0.3xxxxx for [CO] and [H2] , [C] = 1 , [H2O] = 1-0.3xxxxxx

all answers in 3 s.f.

ylup

感觉上好像今年的很难叻....(也许是我没太用功吧...）
haiz....structure完了....太多来不及做了....完了完了....

idontwant2b

原帖由 ylup 于 24-11-2009 12:46 PM 发表
感觉上好像今年的很难叻....(也许是我没太用功吧...）
haiz....structure完了....太多来不及做了....完了完了....

我算到０．３２８，那应该对了！
七分耶！

其实也算容易了，
看去年的更难，
今年ｓｔｒｕｃｔｕｒａｌ蛮难的。

Dicardo

原帖由 darksider 于 24-11-2009 12:45 PM 发表


0.3xxxxx for [CO] and [H2] , [C] = 1 , [H2O] = 1-0.3xxxxxx

all answers in 3 s.f.

.....惨了。。。 我好像忘记看significan number...

idontwant2b

原帖由 Dicardo 于 24-11-2009 02:12 PM 发表


.....惨了。。。 我好像忘记看significan number...

即使如此，也是最后答案扣一分而已…

appletlv

原帖由 ylup 于 24-11-2009 12:46 发表
感觉上好像今年的很难叻....(也许是我没太用功吧...）
haiz....structure完了....太多来不及做了....完了完了....

你和我一样的状况

laiverson

明天math t paper 1 了 大家繼續加油吧...