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Author Topic: IGCSE CHEMISTRY DOUBTS  (Read 27989 times)

Offline sarasa

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #150 on: June 06, 2010, 03:37:45 pm »
Wat is da structural formula of Germanium oxide?
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Offline Ghost Of Highbury

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #151 on: June 06, 2010, 03:45:25 pm »
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divine intervention!

Offline NidZ- Hero

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #152 on: June 06, 2010, 08:56:49 pm »
It is now known that the smell of the seaside is due to the chemical dimethyl sulfide,
(CH3)2S.
(i) Draw a diagram that shows the arrangement of the valency electrons in one
molecule of this covalent compound.
Use x to represent an electron from a carbon atom.
Use o to represent an electron from a hydrogen atom.
Use ? to represent an electron from a sulfur atom.

 i m alwasy confused by this


thanz 4 de help
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Offline Vin

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #153 on: June 06, 2010, 09:01:47 pm »
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Offline Lariemeeva

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #154 on: June 06, 2010, 09:12:28 pm »
Can anyone explain in terms of ions and electrons why steel does not rust when covered with zinc. I think I have some misconceptions on this part.
Thanks in advance.
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Offline NidZ- Hero

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #155 on: June 06, 2010, 09:17:53 pm »
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Offline Vin

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #156 on: June 06, 2010, 09:23:25 pm »
Quote from: Lariemeeva on June 06, 2010, 09:12:28 pm
Can anyone explain in terms of ions and electrons why steel does not rust when covered with zinc. I think I have some misconceptions on this part.
Thanks in advance.

OK,zinc is welded over iron (in case of a ship). It is more reactive so it gives up e- to form +ve ions more readily. So the zinc dissolves..

2Zn ----> 2Zn2+  +  4e-  (oxidation)

The electrons flow to the iron, which passes them on..

O2  +  2H2O  +  4e-  --->  4OH-

Adding the incomplete reactions

2Zn  +  O2  +  H2O ----> 2Zn(OH)2
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Offline Vin

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #157 on: June 06, 2010, 09:24:51 pm »
Quote from: Nidzzz on June 06, 2010, 09:17:53 pm
thanz n hw wuld do u draw structure of diamond

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Offline TheLonelyIsland

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #158 on: June 06, 2010, 09:27:55 pm »
Zinc forms positive ions more easily than iron (more reactive), basically it gets oxidized faster in a reaction with oxygen from air to form zinc oxide. When oxidized, it loses electrons (always) to the metal it protects, so iron in this case has a constant supply of electrons, therefore isn`t in a danger of losing them. The same is with cathodic protection in which electricity connected to the metal supplies it with electrons... Basically preventing the metal to form positive ions, aka, give electrons away... I hope this explanation is sufficient  ;)
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Offline Lariemeeva

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #159 on: June 06, 2010, 09:29:43 pm »
Thanks VIN and TLI~
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Offline TheLonelyIsland

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #160 on: June 06, 2010, 09:31:52 pm »
also, plz, when a gas is collected from a reaction, why does it have to pass through a liquid, and then finally be collected, and what role does the type of a liquid play in all this? Help, plz, don`t get it...
 :)
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Offline TheLonelyIsland

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #161 on: June 06, 2010, 09:51:39 pm »
Anyone?... Pretty please?
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Offline Vin

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #162 on: June 06, 2010, 09:57:36 pm »
Quote from: TheLonelyIsland on June 06, 2010, 09:31:52 pm
also, plz, when a gas is collected from a reaction, why does it have to pass through a liquid, and then finally be collected, and what role does the type of a liquid play in all this? Help, plz, don`t get it...
 :)

Er, I don't really know the exact reason but a gas is collected over because it is insoluble in water and it is more convenient. Sorry I couldn't help you much. i would be waiting for an accurate answer too. :-[
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Offline TheLonelyIsland

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #163 on: June 06, 2010, 10:04:02 pm »
Thanks anyway! You know what I mean though, right? For example in catalytic cracking, when an alkene is collected, the delivery tube first passes through water... why? Why not just downward delivery? That`s just an example though, there are other reactions involving another liquid, not water...

Anyway, good luck!   
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Offline NidZ- Hero

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Re: IGCSE CHEMISTRY DOUBTS
« Reply #164 on: June 06, 2010, 10:49:02 pm »
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