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Author Topic: Chemistry Help HERE ONLY !!  (Read 107204 times)

Offline Naruto

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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #90 on: May 26, 2009, 06:08:55 pm »
well i think that colour will be black ,because iodide is reduced to iodine and it is a black solid in colour... +rep if i m correct  ;)
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Offline Shogun

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Re: Chemistry Help HERE ONLY !!
« Reply #91 on: May 26, 2009, 06:36:16 pm »
hey lana

it goes like this


3 mols of co2 give 15 cm3
so what will 5 mols of oxygen give?
its simply cross multiplication

no. of mols                 volume
     3                            15
     5                              ?

so (5 x 15)
   ---------= 25cm3
        3

then to get the volume for propanol (C3H8) which is 1 mol ,do the same

no. of mols                   volume
      3                              15
      1                                ?
 
so    (1 x 15)
     ----------  = 5cm3
           3

so the answer is for oxygen=25     and   for  propanol=5

hope u understand, any confusion or difficluties or help, plz do ask me
« Last Edit: May 26, 2009, 06:38:06 pm by Shogun »
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Offline ap105

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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #92 on: May 26, 2009, 09:55:57 pm »
@ gonnagetana:

Hello ! I'm new here .... ermm ... Potassium iodide by itself is white in colour .... Aged and impure samples are yellow because of
oxidation of the iodide to iodine ...

Since the iodide ion is a mild reducing agent, I? is easily oxidised to I2 by powerful oxidising agents such as chlorine:

    2 KI(aq) + Cl2(aq) ? 2 KCl + I2(aq)

This reaction is employed in the isolation of iodine from natural sources. Even air will oxidize iodide as evidenced by the observation of a purple extract when aged samples of KI are rinsed with dichloromethane. As formed under acidic conditions, hydroiodic acid (HI) is a stronger reducing agent.[3][4][5]

Like other iodide salts, KI forms I3? when combined with elemental iodine.

    KI(aq) + I2(s) ? KI3(aq)

Unlike I2, I3? salts can be highly water-soluble. Through this reaction iodine is used in redox titrations. Aqueous KI3, "Lugol's solution," are used as disinfectants and as etchants for gold surfaces.

Potassium iodide is the precursor to silver(I) iodide, which are used for high speed photographic film:

    KI(aq) + AgNO3(aq) ? AgI(s) + KNO3(aq)

Hence, Chlorine is reacted with KI to obtain Iodine

KI + HCl (strong reducing agent - stronger than the iodide ion) --> No reaction -- both reagents are water soluble
 
Source: Wikipedia & http://answers.yahoo.com/question/index?qid=20070919134841AAUqbvK ... :P

Hope this helps !
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Offline Nanavel

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Re: Chemistry Help HERE ONLY !!
« Reply #93 on: May 26, 2009, 10:15:41 pm »
An alloy contains zinc and Copper . A small sample of this alloy was dissolved in acid to give a soluion containing zinc and copper ions.
Explain what would happen when an excess of each of the following reagents is separatly added to this solution.

i) Iron Fillings

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

------------------------------------------------------------------------------------------ [2]

ii) Sodium Hydroxide
------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------ [2]


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Offline MaNa

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Re: Chemistry Help HERE ONLY !!
« Reply #94 on: May 26, 2009, 10:31:15 pm »
i am not sure but
when NaOn is added to a solution contain Cu Deep dark blue solution is foremed
n even with Zn it forms White ppl :S
wite Iron filing i guess the solution turns into blue to grrenish/reddish :S
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Offline AS girl

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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #95 on: May 26, 2009, 10:35:52 pm »
Quote from: gonnagetana on May 26, 2009, 04:21:41 pm
Hey, does anyone know what colour change occurs when potassium iodide is reduced??? Its in the syllabus, you gotta know this!!!!


Colour changes from colourless to dark brown and a black solid may form as well ;)hope i helped
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Offline Nanavel

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Re: Chemistry Help HERE ONLY !!
« Reply #96 on: May 26, 2009, 10:40:18 pm »
I was thinking the same too but i thought i was wronge .. (+rep) Thanx for the help
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Offline MaNa

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Re: Chemistry Help HERE ONLY !!
« Reply #97 on: May 26, 2009, 10:46:18 pm »
Quote from: Nanavel on May 26, 2009, 10:40:18 pm
I was thinking the same too but i thought i was wronge .. (+rep) Thanx for the help
lol its ok which yr was this question in?
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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #98 on: May 26, 2009, 10:47:47 pm »
Quote from: IG girl on May 26, 2009, 10:35:52 pm
Quote from: gonnagetana on May 26, 2009, 04:21:41 pm
Hey, does anyone know what colour change occurs when potassium iodide is reduced??? Its in the syllabus, you gotta know this!!!!


Colour changes from colourless to dark brown and a black solid may form as well ;)hope i helped


+REP u for the 2nd time as i promised!!
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Offline AS girl

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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #99 on: May 26, 2009, 10:54:46 pm »
Quote from: Monica on May 26, 2009, 10:47:47 pm
Quote from: IG girl on May 26, 2009, 10:35:52 pm
Quote from: gonnagetana on May 26, 2009, 04:21:41 pm
Hey, does anyone know what colour change occurs when potassium iodide is reduced??? Its in the syllabus, you gotta know this!!!!


Colour changes from colourless to dark brown and a black solid may form as well ;)hope i helped


+REP u for the 2nd time as i promised!!



l ;D
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Offline AS girl

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Re: Chemistry Help HERE ONLY !!
« Reply #100 on: May 26, 2009, 10:58:40 pm »

An alloy contains zinc and Copper . A small sample of this alloy was dissolved in acid to give a soluion containing zinc and copper ions.
Explain what would happen when an excess of each of the following reagents is separatly added to this solution.

i) Iron Fillings
effervescenses-bubbles of colourless gas. With lighted splint it pops (Hydrogen)
------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------ [2]

ii) Sodium Hydroxide
------------------------------------------------------------------------------------------
zinc-white precipetation soluble in excess
------------------------------------------------------------------------------------------ [2]
Copper-blue ppt becomes soluble in excess solution changes to deep blue(royal)







I'm not sure of the answer!!
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Offline gonnagetana

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Re: Chemistry 2009!!! Paper 3 prep.....
« Reply #101 on: May 27, 2009, 02:13:45 am »
thats interesting, i got a whole bunch of different answers
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Offline archangel

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Re: Chemistry Help HERE ONLY !!
« Reply #102 on: May 27, 2009, 08:34:55 am »
Quote from: IG girl on May 26, 2009, 10:58:40 pm

An alloy contains zinc and Copper . A small sample of this alloy was dissolved in acid to give a soluion containing zinc and copper ions.
Explain what would happen when an excess of each of the following reagents is separatly added to this solution.

i) Iron Fillings
effervescenses-bubbles of colourless gas. With lighted splint it pops (Hydrogen)
------------------------------------------------------------------------------------------

------------------------------------------------------------------------------------------ [2]

ii) Sodium Hydroxide
------------------------------------------------------------------------------------------
zinc-white precipetation soluble in excess
------------------------------------------------------------------------------------------ [2]
Copper-blue ppt becomes soluble in excess solution changes to deep blue(royal)


I'm not sure of the answer!!

the first one:
the iron fillings would displace the copper while the iron filings would be displaced by zinc, bcoz it is more reactive than iron.
brown red solid will be found on the bottom on the beaker.

second one:
zinc- white ppt. souble in excess giving colourless solution
copper - light blue ppt. formed in excess
[blue ppt. soluble in excess giving dark blue solution is for aqueous ammonia]

i hope its correct and this helps =)
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Offline zubair_slipknot

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Re: Chemistry Help HERE ONLY !!
« Reply #103 on: May 27, 2009, 08:58:33 am »
Reactivity table    /\
                         |
Potassium            |
Sodium                |
Calcium               |
Magmesium          |
aluminium            |
carbon               |
zinc                   |
iron                   |
tin                    |    Increasing of reactivity
lead                  |
hydrogen           |
copper              |
silver                |
gold                  |
platinum            |


Sorry could not draw a good arrow for the increasing of reactivity...hope this helps
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Offline sweetsh

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Re: Chemistry Help HERE ONLY !!
« Reply #104 on: May 27, 2009, 09:01:41 am »
I know it like this
K
Na
Li
Ca
Mg
Al
Zn
Fe
Sn
Pb
Cu
Ag
Au
Pt
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