Term 1-Chemistry讨论区

晨曦_1515

Allmaths 发表于 21-6-2014 06:35 PM
1) Calculate:

a) 1g/mL = density of water

书本的答案是a)5.56 x 10^23  b)3.34 x 10^25 耶 是答案错了吗？?

Allmaths

晨曦_1515 发表于 21-6-2014 07:07 PM
书本的答案是a)5.56 x 10^23  b)3.34 x 10^25 耶  是答案错了吗？?

靠谱。。差这么远

paiseh的说一句，  答案是google出来的

doeramon

晨曦_1515 发表于 21-6-2014 07:07 PM
书本的答案是a)5.56 x 10^23  b)3.34 x 10^25 耶  是答案错了吗？?

第二题什么答案？
你有打错字吗？dibasic acid?

晨曦_1515

Allmaths 发表于 21-6-2014 07:44 PM
靠谱。。差这么远

paiseh的说一句，  答案是google出来的

没关系啦~ 还是谢谢你哦

晨曦_1515

doeramon 发表于 21-6-2014 07:47 PM
第二题什么答案？
你有打错字吗？dibasic acid?

没打错啊~ 我确认了~  2.的答案是93.8哦

doeramon

晨曦_1515 发表于 21-6-2014 05:49 PM
哈喽~ 又来问多两题了 stpm自修真的好辛苦 学校老师又经常不见人影 希望能够撑得下去 ...

2)我google search了，才知道dibasic acid是H2SO4
H2SO4 +2NaOH ———>Na2SO4+ 2H2O

no of mol NaOH :32 x 0.1/1000=3.2x10^-3 mol
1 mol of H2SO4 react with 2 mol of NaoH
? mol of H2SO4 react with 3.2x10^-3mol of NaoH
要找H2SO4的mol就要把NaOH 的mol除2 ，就会找到1.6x10^-3mol

H2SO4
1.6x10^-3 =0.15/ atomic mass
atomic mass=93.8

doeramon

1) 为什么B 是3个single covalent bond?而不是2 single covalent+ 1 double covalent?
3 个single covalent都只有6个e
2 single covalent+ 1 double covalent(把其中一个Cl的2个e share给 B)才有8个eB)

2）S为什么有10个valence electron?
S 为什么不可以3个single covalent bond?

上一次的问题还没人解答
1)为什么ionic bond 的metal会是low ionisation energy,而不是high ionisation energy?
2)为什么MgO 的melting point高过NaCl？
3）在form ionic bond 的时候，为什么是large size cation and small size anion?
4) excited state的时候做么electron要分开画，不可以有pair?
  .                  .
. C ..   ---->  . C .
                      .
Ground       excited
state            state

树熊123

doeramon 发表于 30-6-2014 08:36 PM
1) 为什么B 是3个single covalent bond?而不是2 single covalent+ 1 double covalent?
3 个single covalen ...

希望帮得到你(^_^)

polygon0121

想问问第4题该怎么做啊？？？我这么做对吗？

题目

我做的。。。

MichelleLow

help explaining the below question:
-How many spectral lines can be produced by the electronic transitions between the three lowest energy levels in hydrogen atom? The answer is 3.
-Why not 2 ??

doeramon

树熊123 发表于 4-7-2014 04:53 PM
希望帮得到你(^_^)

为什么不可以这样画？

doeramon

MichelleLow 发表于 5-7-2014 04:56 PM
help explaining the below question:
-How many spectral lines can be produced by the electronic tran ...

我借polygon 发出来的图片跟你解释
hydrogen只出现在balmer和lyman series罢了
问题说three lowest energy就是n=1,2,3 ,所以n=4,5,...就不需要看了

树熊123

doeramon 发表于 6-7-2014 07:45 PM
为什么不可以这样画？

顺便问下这里谁有用微信？
我建议大家在微信开个组讨论(^_^)
如果有开请加我，微信号wcyabc0603，谢谢！

aktf

doeramon 发表于 30-6-2014 08:36 PM
1) 为什么B 是3个single covalent bond?而不是2 single covalent+ 1 double covalent?
3 个single covalen ...

这些解释是google search出来。。不知道能不能帮你解释

1）The general pattern of the ionization energy as they are in regard to the period table is that the IE increases across a period, and decreases down a group. Because it requires more energy to remove an electron from a stable atom, the noble gases are usually associated with the highest IE1. Because their valence shells are already filled and stablized, they will require much more energy to disrupt that stability. The first electron that is expelled is the most loosely held to the atom.

2）其实他有很多原因能影响它的melting point。
Both compounds are ionic.  As such they are held together by the electrostatic attractions between cations and anions.  In MgO, the cations are Mg²⁺ and the anions are O²⁻; in Na Cl it's Na⁺ and Cl⁻.  The greater charge in MgO means that the Coulomb attrasctions are 4 times bigger (2 × 2, assuming equal distances).  Therefore, MgO ionic bonding is much stronger than NaCl ionic bonding.

3）Cations are formed when an electron is lost.  When this occurs there are less electron-electron repulsions and there is a greater net nuclear attraction per electron. So, the newly formed ion becomes a more condensed version of its neutral atom.  Anions are formed when an electron is gained.  When this occurs there are more electron-electron repulsions and there is a lower net nuclear attraction per electron.  This will cause the electrons push each other away and spread out, causing the atom to become larger.  

4）这题应该是要看他的hybridisation，通常都是一个electron一个electron excited 的

polygon0121

话说我又来问问题了，请问第(a)题的part (ii)要怎么写equation？？？还有那个 number of mole of helium gas要怎么找？？？求指教。。。

题目：

weston123453

chemistry refference bk which one better ,LONGMAN or OXFORD FAJAR?

MichelleLow

How can i know which molecule should undergo sp hybridisation, sp^2 hybridisation or sp^3 hybridisation??
For example is CO2, why the textbook wrote it undergoes sp hybridisation not sp^3? Didn't it have 8 electrons so it has 4 orbital, than undergoes sp^3??
-Help explanning ><, and pls show me how the energy level diagram change and cause there is have one unhybridise

doeramon

MichelleLow 发表于 18-7-2014 07:35 PM
How can i know which molecule should undergo sp hybridisation, sp^2 hybridisation or sp^3 hybridisat ...

..                ..
O  =   C =  O
..               ..
hybridisation是看centre atom 的
画了lewis structure ,就可以看到centre atom有多少个bond
double bond 也算成1个 S
another double bond   P
hybridise SP

MichelleLow

doeramon 发表于 18-7-2014 07:56 PM
..                ..
O  =   C =  O
..               ..

那如何知道有unhybridise in the molecule?

MichelleLow

weston123453 发表于 18-7-2014 12:38 AM
chemistry refference bk which one better ,LONGMAN or OXFORD FAJAR?

still hav longman, this publisher??i just saw pelangi and oxford only..
For my teacher's opinion said that oxford is basically while the content in pelangi quite difficult to know what the contents say becos those quite straight forward to give information only, not further explanation..
so up to u lor~