STPM化学专区

卡莉。谢

chemistry 的calculation 就快把我杀死了～

暴杀·憾雨泪

hydrochloric acid是不是ionic bond来的？
H和Cl都是非金属，
但为什么还能dissociate into ions之类的?
而且还能溶在water里，polarising的不是吗？

然后H是第几组的元素来的？

星星之玲

这是physical chemistry 的chapter12 phase equilibrium问题谁能帮我算一下啊?谢谢!

The partition coefficient of a substance X between ether and water is 8.0 .
An  aqueous solution containing 5.0g of X in 100cm^3 of water is extracted with 100cm^3 of ether .
What is the maximum mass of X that can be extracted into the ether layer?


The answer is 4.44g  who can show me the working...please! thank...

fovander

原帖由 wahaha1 于 3-1-2009 03:58 PM 发表
请问有谁可以解释the uniqness of carbon atom AND hybridisation ??

为何不可说catenation of C, ie ability 2 form single, double and triple bond?

wahaha1

原帖由 fovander 于 18-2-2009 06:17 PM 发表

为何不可说catenation of C, ie ability 2 form single, double and triple bond?

err~~
有请前辈指点～
晚辈刚开始自修～

wahaha1

一题对你们来说很简单的问题

bromine consists of two isotopes,79Br and 81Br.
if the Ar of bromine is 79.9
calculate the relative abundance of each of the isotopes.

Ivanlsy

原帖由 wahaha1 于 2-4-2009 07:50 PM 发表
一题对你们来说很简单的问题

bromine consists of two isotopes,79Br and 81Br.
if the Ar of bromine is 79.9
calculate the relative abundance of each of the isotopes.

Let the relative abundance of 79Br = n
therefore the relative abundance of 81Br = 1 - n

79n + 81(1 - n) = 79.9
79n + 81 - 81n = 79.9
(79 - 81)n = 79.9 - 81
-2n = -1.1
n =  0.55 = 55%
1 - n = 0.45 = 45%

Hence the relative abundance of 79Br and 81Br are 55% and 45% respectively.

wahaha1

原帖由 Ivanlsy 于 2-4-2009 08:45 PM 发表

Let the relative abundance of 79Br = n
therefore the relative abundance of 81Br = 1 - n

79n + 81(1 - n) = 79.9
79n + 81 - 81n = 79.9
(79 - 81)n = 79.9 - 81
-2n = -1.1
n =  0.55 = 55%
1 - n ...

thankssssssssss

wahaha1

有谁可以解释关于mass spectrum的东西吗？
要怎样知道是那某个Ion在其m/e的位子？
有方法预测/算到吗？
physical chemistry的第一课而已~

p/s:希望看得懂我讲什么

Allison

Cl-35 就在m/e 35
Cl-37 就在m/e 37
m/e 是mass/ electron

不知道这是不是你要的答案
老实说有点不明白你的题目。。。

wahaha1

原帖由 Allison 于 5-4-2009 04:25 PM 发表
Cl-35 就在m/e 35
Cl-37 就在m/e 37
m/e 是mass/ electron

不知道这是不是你要的答案
老实说有点不明白你的题目。。。

不是~
你讲的有谁不懂
可是如果做练习
我就不懂了~
题目有给specific molecule/comp和m/e
可是我不懂要怎样自己找出在某个m/e ratio时的ion阿~~

不好意思哦，我的问题有点含糊~

wahaha1

另外
m/e ratio也是nucleon no吧？
对吗？

Ivanlsy

原帖由 wahaha1 于 5-4-2009 05:38 PM 发表
另外
m/e ratio也是nucleon no吧？
对吗？

不是~
比如説Ca^(2+) ion，他的m/e ratio是20~
因爲Ca^(2+) ion的mass number (nucleon number)是40，但他的charge是2，所以m/e ratio是 40/2 = 20。

[ 本帖最后由 Ivanlsy 于 5-4-2009 08:39 PM 编辑 ]

cgcy

Mechanism :
NO + F2 -----> NOF + F*
F* + NO -----> NOF
Overall equation:
2NO + F2 -----> 2NOF
Question: Please justify the mechanism in term of reaction kinetics.

cgcy

How the reaction rate be affected by the partial pressure???

cgcy

Can pH affect the reaction rate??

末日审判

各位高手，帮帮下！
1.Selenium,Se,occurs in nature as a mixture of six isotopes having the relative abundance given below:
   nucleon(mass) number           %abundance
                 74                                     0.9
                 76                                     9.0
                 77                                     7.6
                 78                                   23.5
                 80                                   49.8
                 82                                     9.2
Determine the number of neutrons in the least abundant isotope of selenium and write down the electronic    configuration of the selenium atom.

2.In an atom Z,orbitals A and B are full but orbitals C and D are half-filled.
   (i)write down the electronic configuration of atom Z.
3.In an ion Y^2+,the orbitals A, B, C, D, and E are full.
   (i)What is the proton number of element Y?
   (ii)What is the likely relative atomic mass of element Y?

白羊座aries

Which of the following properties decreases when going across the third period from sodium to argon.
1 Density
2 Atomic radius
3 Metallic character

1  density到底是不是decreases when going acrosss period??请帮忙解释

chee_yong

what are the question mighth come out in 2009?
what is the most important thingsto notice when study phy.chem organic and inorganic chem?
heip pls.

秋分

rate=Ae-(EA/RT)
所以,自己看ph有没有影响rate