STPM化学专区

Dicardo

so if it only written 'aqueous' , we can assume it is dilute ?

darksider

原帖由 Dicardo 于 2009/8/27 11:32 AM 发表
so if it only written 'aqueous' , we can assume it is dilute ?

Yes, most probably. If it never mentions concentrated salt, then it should be a dilute one.

darksider

做了些改正，有错的地方就提醒我吧！

@影子@

帮我解决这问题

A glass bulb contains 4.0g of gas at a pressure of 100kPa. If the pressure in the bulb is lowered to 0.1kPa by removing the gas in it,what is the number of molecules that will be left in the bulb?(Mr of gas=40 ; Avogadro constant = 6 X 10^23)

darksider

原帖由 @影子@ 于 2009/8/27 08:56 PM 发表
帮我解决这问题

A glass bulb contains 4.0g of gas at a pressure of 100kPa. If the pressure in the bulb is lowered to 0.1kPa by removing the gas in it,what is the number of molecules that will be lef ...

Take note that the volume of glass bulb is constant.
Initially, at pressure of 100kPa, there is 4.0g of the gas.
Hence, at 0.1kPa, there is x g of gas.

100000 Pa = 4g
        100Pa = xg
x= 4x100 / 100000
  = 4/1000 = 0.004g

mol of the gas = 0.004g / 40 g per mol
                         =  0.0001 mol

Therefore, number of molecules of the gas left = 0.0001mol x 6.022x10^-23 per mol
                                                                               = multiply yourself

@影子@

1.In temperature T K,1dm³ of an equilibrium mixture contains 0.60mol N2,0.50 mol O2 and 0.15 mol NO.
(a)Calculate the equilibrium constant Kc at T K for the following equilibrium:
                                   N2(g) + O2(g) ~~~~2NO(g)                          ~~~represent forward n backward reaction
(b)0.20 mol N2 is then added to the equilibrium mixture,whilst maintaining the temperature  at T K. Calculate the value of      (NO)²       at the moment when N2 is introduced into the mixture.
         （N2）（O2）
(c)Calculate the concentration of N2,O2 and NO at the new equilibrium.



2.                             2NO(g) + Cl2 ~~~~ 2NOCl(g)
At temperature T℃，the partial pressures of NO,Cl2 and NOCl in a 1dm³ equilibrium mixture are 60kPa, 50kPa and 80kPa respectively.
(a) Calculate the value of the equilibrium constant,Kp.
(b) When additional Cl2 is added so that its partial pressure is 70atm, the new equilibrium partial pressure of NOCl is 88atm.Determine the partial pressures of NO and Cl2 in the new equilibrium mixture if temperature remains constant.

darksider

http://www.youtube.com/watch?v=CGJjjm7-DJ4

@影子@

什么意思啊？

darksider

去看看
Reaction in Equilibrium
http://www.youtube.com/watch?v=C ... =player_profilepage

Intuition behind formula of Keq
http://www.youtube.com/watch?v=O ... =player_profilepage

Le Chatelier's principle
http://www.youtube.com/watch?v=4 ... =player_profilepage

那些问题都很简单，你去看这些video后明白了才做。

Tips for 1(c)  Calculate concentration at new equilibrium
                      N2        +            O2  <------>  2NO
Initial             6+2                      5                   1.5
Change          -x                       -x                  +2x
equilibrium   8-x                     5-x                  1.5+2x
(new)
Since Keq is only affected by changes in temperature, hence it remains constant when concentration of N2 increases.

Therefore, Keq = 0.075 = (1.5+2x)^2 / (8-x).(5-x)
Find x and you will get the answer but substituiting x into concentraton at new equilibrium.

@影子@

噢，好！
我不会再问！
谢谢你！

idontwant2b

请问
hydrolysis, condensation, hydration, dehydration分别在哪里？

premier66

hydration 是加 H2O ,dehydration 是把H2O 弄走 ， hydrolysis 是把H2O 分解， 有两种 alkaline hydrolysis :normally we use  sodium hydroxide ,NaOH to produce OH ions , another type is acidic hydrolysis :use sulphuric acid ,H2SO4 ,to get H ions.

大概是这样。。。

darksider

原帖由 idontwant2b 于 2009/10/9 08:52 PM 发表
请问
hydrolysis, condensation, hydration, dehydration分别在哪里？

Hydrolysis is a reaction that involves breaking down of water molecules.[Alkaline hydrolysis, acidic hydrolysis etc]

Condensation is a reaction involving formation of water molecules. [Condensation polymerisation etc]

Hydration is reaction involving addition of water molecules(act as ligands) to a molecule or compound.
eg, Cu2+ + 6H2O ----> [Cu(H2O)6]2+

Dehydration is a reaction that involves removal of H and OH atoms from a compound to form H-OH (water)

nkrealman

有什么简单的方法去读thermochemistry这课？
尤其是born-haber cycle.
还有 hybridisation要怎样看？

darksider

原帖由 nkrealman 于 2009/10/29 02:35 AM 发表
有什么简单的方法去读thermochemistry这课？
尤其是born-haber cycle.
还有 hybridisation要怎样看？

thermochemistry..
明白所有enthalpy change...可以去www.khanacademy.org参考。
你需知道怎样
-enthalpy change of reaction = enthalpy change of formation of product - enthalpy change of formation of reactant
-enthalpy change of combustion
-enthalpy change of solution = - Lattice energy + enthalpy change of hydration
-explain the enthalpy change of neutralisation of weak acid/base (energy absorbed to dissociate weak base/acid)
-hess's law ... enthalpy change is a state variable... enthalpy change of a reaction is independent of the route it takes to complete the reaction.
-born haber cycle is used to calculate ionisation energy.
若arrow向上，你用+sign，若arrow向下，你用negative sign.

in born haber cycle，
total energy in the LHS = total energy in the RHS
- assume all arrows are heading upwards in both sides(change sign if necessary). then equate both and you will be able to find the desired value.

-------------------------------------------
hybridisation is the fusion of orbitals of different energy levels to degenerate orbitals in order to faciliatate bonding.
There are three types in our syllabus.... sp, sp2, sp3...

[ 本帖最后由 darksider 于 29-10-2009 08:24 AM 编辑 ]

idontwant2b

请问考试complex的颜色要背吗？
2008的好像要背的耶。

darksider

原帖由 idontwant2b 于 2009/11/8 11:03 PM 发表
请问考试complex的颜色要背吗？
2008的好像要背的耶。

对。。要背。。但是来来去去都是一样。。。

idontwant2b

可以列列哪几种吗？
本人inorganic原本都不好了，
现在才知道连那些reagent颜色也要背，
2008出了，2009还是可能出。

Dicardo

原帖由 idontwant2b 于 8-11-2009 11:03 PM 发表
请问考试complex的颜色要背吗？
2008的好像要背的耶。

重要的才要被。。。像CuSO4, CuCl4

darksider

原帖由 idontwant2b 于 2009/11/9 01:10 AM 发表
可以列列哪几种吗？
本人inorganic原本都不好了，
现在才知道连那些reagent颜色也要背，
2008出了，2009还是可能出。

Cr(3+)(aq)
Cr(OH)3 (green ppt) ;
add NaOH in excess---> [Cr(OH)6](3-) ... green solution
add NH3 in excess ---> [Cr(NH3)6(3+) ... green solution

Fe(2+)(aq)
Fe(OH)2 dark green ppt ;
add NaOH in excess ---> Fe(OH)3 dark brown ppt (oxidation)
add NH3 in excess --->  Fe(OH)3 dark brown ppt (oxidation)

Fe(3+)(aq)
add NaOH in excess ---　Fe(OH)3 dark brown ppt
add NH3 in excess --->  Fe(OH)3 dark brown ppt

Co(2+)(aq)
Add NaOH in excess ---> Co(OH)2 blue ppt
add NH3 in ecess ----> Co(OH)2 dissolves to form brown solution of [Co(NH3)6](2+)

Ni(2+）
Add NaOH in excess ---> green ppt of Ni(OH)2
Add NH3 in excess ----> green ppt of  Ni(OH)2 dissolves to form pale blue solution Ni(NH3)6](2+)

Cu2+
Add NaOH in excess ---> Blue ppt of Cu(OH)2
Add NH3 in excess ---> blue ppt of Cu(OH)2 dissolves to give deep blue solution of [Cu(NH3)4] (2+)

This also remember (in neutral solution) ; water acts as ligand
Copper
[Cu(H2O)6](2+) + NH3 (in excess) ----> [Cu(NH3)4]2+
pale blue                                                 deep/dark blue

[Cu(EDTA)]2+ --- light blue  ; CuCl4(2-) ---- yellow

Cobalt
[CoCl4]2- + 6H2O ---->  [Co(H2O)6]2+ + 4Cl-
blue                                         pink

[Co(NH3)6]2+ --- yellow ; [Co(H2O)6]3+ --- brown

Iron
*[Fe(H2O)6]2+ --- pale green ; [Fe(H2O)6]3+ --- yellow
[Fe(CN)6]4- & [Fe(CN)6]3- --- yellow
[Fe(H2O)5SCN]2+ --- blood red [ SCN(-)... Fe here is Fe3+]

Nickel
[Ni(H2O)6]2+ --- light green >>>>> [Ni(NH3)6]2+ --- light blue

Chromium
[Cr(H2O)6]2+ ---blue
[Cr(H2O)6]3+ ---green/violet
[Cr(OH)6]3-  ---bright green
[Cr(H2O)5Cl]2+ -- light green >> [Cr(H2O)4Cl2]+ --- dark green

Cr2O7(2-) --- orange [ stable in acidic condition ; K2Cr2O7 ]
CrO4(2-) --- yellow [ stable in alkaline condition]

Manganese
[Mn(H2O)6]2+ --- light pink
MnO4- --- Purple [ Stable in acidic condition ; KMnO4]
MnO4(2-) --Green [ stable in alkaline condition]

------------------------------------------------------------------------------------

你选那些比较重要的来记起来，比如那些colour change when displacement of ligands occurs.
如果要记住全部的话，也不难。一个一个去imagine,这要看你的想象力。〔visualise 它们〕

[ 本帖最后由 darksider 于 9-11-2009 10:31 AM 编辑 ]