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Author Topic: Chemistry Help HERE ONLY !!  (Read 106273 times)

Offline ramezamgad

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Re: MOLES
« Reply #360 on: May 30, 2009, 01:28:06 am »
the 3 rules for moles

1) No. of moles = Mass / (Mr or Ar)          -----> for solids
2) No. of moles = Volume x concentration  -----> for liquids
3) No. of moles = Volume / 24                 -----> for gases

in the second eq. the volume should be in dm3 and conc. in mol/dm3
24 is the volume in dm3 of 1 mole of any gas at room temperature and pressure
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Offline Nanavel

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Re: Chemistry Help HERE ONLY !!
« Reply #361 on: May 30, 2009, 03:12:39 am »
you all are SUPERB ! lil wyne >> you are guranteed an A* already ... I wish i was this awesome as you are  ..  double + rep

so is shogun .. I learned alot of things from you guys .. Thanx alot for helping all of us out .. Insha'llah i will get A* too  >> very optimistic >> did alot of sillyness in paper 6 actually in chemistry and Biology i screwed in them  not because i dont know the anwers because i am all doing the paper with hurry and excitment and i dont read full questions .. so i mess up alot

I hope i wont do any stupidity this time
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Offline aquarian93

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Re: Chemistry Help HERE ONLY !!
« Reply #362 on: May 30, 2009, 04:38:27 am »
u guys
"what property of SO2 enables it be used as a bleaching agent?"
thanks!
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Offline hell_devil

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Re: Chemistry Help HERE ONLY !!
« Reply #363 on: May 30, 2009, 04:59:46 am »
what r da imprtant things dat we ned 2 learn frm application part???????i don undrstand anythin frm da part....
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Offline aquarian93

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Re: Chemistry Help HERE ONLY !!
« Reply #364 on: May 30, 2009, 05:02:16 am »
Quote from: ~M.J~ on May 29, 2009, 06:15:50 pm
Quote from: kam on May 29, 2009, 06:07:19 pm
Quote from: abdulrahman101 on May 29, 2009, 05:39:03 pm
Quote from: ZeroZero82 on May 28, 2009, 10:48:27 am
how do we know if a reaction is endothermic?!

The temp would fall, this is because it takes more energy/heat to break the bonds between the atoms, if it was exothermic, then more energy would be used to form new bonds, and the temp. raises

correct me if im wrong but i thought it was the other way round
cuz endo takes in heat so temp rises(positive)
and exo gives out heat go temp falls(negative)
the heat source always has a higher temperature than the surrounding
in a redox reaction heat is not displaced it is either produced or used up
here the temperature is referred to the surrounding not the reagents
so in an exothermic reaction heat is produced which increasaes the temp. of the surrounding   so the temperature is increased

so do u mean dat is according to the surrounding?
so exothermic (even if heat is given out) the temp increases
and endothermic (even if heat is absorbed) the temp decreases

so its abt the surrounding rite?  ???
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Offline AN10

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Re: Chemistry Help HERE ONLY !!
« Reply #365 on: May 30, 2009, 05:18:06 am »
Quote from: aquarian93 on May 30, 2009, 04:38:27 am
u guys
"what property of SO2 enables it be used as a bleaching agent?"
thanks!
sulphur dioxide is a good reducing agent. In the presence of water, it is able to decolourize substances.
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Offline guru007

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Re: Chemistry Help HERE ONLY !!
« Reply #366 on: May 30, 2009, 05:40:33 am »
Quote from: Q80BOY on May 21, 2009, 06:22:57 pm
hey guys,

as the chemsitry exam is on the 1st of june, u must all be revising, and u MUST have some questions,

so if u have any CHEMISTRY questions, post them here and hopefully some one will help.

Gd Luck  :)



Hey Q80BOY
can u plz explain me extraction of aluminium ???
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Offline aquarian93

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Re: Chemistry Help HERE ONLY !!
« Reply #367 on: May 30, 2009, 05:43:45 am »
Quote from: AN10 on May 30, 2009, 05:18:06 am
Quote from: aquarian93 on May 30, 2009, 04:38:27 am
u guys
"what property of SO2 enables it be used as a bleaching agent?"
thanks!
sulphur dioxide is a good reducing agent. In the presence of water, it is able to decolourize substances.
thank you! :)
+REP
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Offline guru007

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EXTRACTION OF METALS
« Reply #368 on: May 30, 2009, 05:50:53 am »
Can someone help me in extraction of zinc and aluminium ???
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Offline thukon

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Re: EXTRACTION OF METALS
« Reply #369 on: May 30, 2009, 06:55:06 am »
for zinc, u heat the ore (zinc blende, or zinc sulphide) and it will become zinc oxide and sulphur dioxide. Then u reduce the zinc oxide with carbon monoxide. For aluminium, u have to add sodium hydroxide to the aluminium ore (bauxite) get rid of the iron III oxide impurities. The result is alumina or aluminium oxide. Dissolve this alumina in molten cryolite (to lower the temperature needed for the electrolysis) and then electrolyse it. U get aluminium. The anode is graphite. The cathode is steel i think.
« Last Edit: May 30, 2009, 06:58:30 am by thukon »
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Offline aquarian93

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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #370 on: May 30, 2009, 07:04:59 am »
do we need to noe the % of carbon, properties and uses of carbon steels?
and do we need to noe the metals added, properties and uses of alloy steels?
???
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Offline saifalan

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Re: MOLES
« Reply #371 on: May 30, 2009, 07:12:58 am »
1 mole,n = 6.023 x 10^(23) of any gas particles.

6.023 x 10 ^(23) is also called the Avogardo Constant, NA.

Total no. of particles, N= nNA
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Offline aquarian93

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Re: Chemistry Help HERE ONLY !!
« Reply #372 on: May 30, 2009, 08:12:58 am »
do we need to noe the % of carbon, properties and uses of carbon steels?
and do we need to noe the metals added, properties and uses of alloy steels?
???
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Offline X Abdulrahman X

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Re: Chemistry Help HERE ONLY !!
« Reply #373 on: May 30, 2009, 08:27:58 am »
Quote from: aquarian93 on May 30, 2009, 08:12:58 am
do we need to noe the % of carbon, properties and uses of carbon steels?
and do we need to noe the metals added, properties and uses of alloy steels?
???

Yup it does come up sometimes, and they are easy 2-4 marks :)
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Offline ig_kid

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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #374 on: May 30, 2009, 08:29:50 am »
Yes...u need 2 noe all these stuff. ;)
Its annoying cz we hv alot 2 study and not enough time.
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