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Topic: Identification of ions and gases  (Read 9883 times)

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Offline alicia_tan2113

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Identification of ions and gases
« on: December 30, 2010, 07:50:29 AM »
Describe a simple test, other than displacement, that can be used to show that sea water contains iodide ions.
Test:
Result:______________________________________________________________________________________________________________________________________________

I got stuck at this last question in my exam paper so I just need someone to go through this with me:)

Offline Evaldas

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Re: Identification of ions and gases
« Reply #1 on: December 30, 2010, 08:06:33 AM »
Starch? Cos for example to prove that a potato contains starch you take tincture of iodine and put a few drops and the starch particles change color into a dark blue.

Offline Fluorine

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Re: Identification of ions and gases
« Reply #2 on: December 30, 2010, 08:14:50 AM »
Silver nitrate test will give a precipitate...though if you have other halides it may cause a bit confusion. I did a lab on this though I recall very little of the procedure.
I'm still learning - always check my work/answer.

"curse Pierre Jules César Janssen!"

Offline Evaldas

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Re: Identification of ions and gases
« Reply #3 on: December 30, 2010, 08:20:28 AM »
Silver nitrate test will give a precipitate...though if you have other halides it may cause a bit confusion. I did a lab on this though I recall very little of the procedure.
But "other than displacement".

Offline alicia_tan2113

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Re: Identification of ions and gases
« Reply #4 on: December 30, 2010, 08:27:49 AM »
Thats why i couldn't think of anything xD

Offline Fluorine

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Re: Identification of ions and gases
« Reply #5 on: December 30, 2010, 05:17:25 PM »
I read over that part somehow - oops.
I'm still learning - always check my work/answer.

"curse Pierre Jules César Janssen!"

Offline alicia_tan2113

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Re: Identification of ions and gases
« Reply #6 on: December 30, 2010, 08:32:35 PM »
I learnt chromatography,decanting, filtration, evaporating to dryness, crystallization, sublimation... I wonder if that helps.

Offline Twigg

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Re: Identification of ions and gases
« Reply #7 on: December 31, 2010, 11:04:53 PM »
Ooooh I used to know this. There's a soluble compound that changes color in the presence of different halogen ions but I can't remember it! I *think* it's AgNO3 or some other silver-based salt.

@Evaldas, that's what I was thinking. I don't think seawater would behave the same way as the tincture though. If it does... I am throwing out my Lugol's solution  ;D

Offline Evaldas

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Re: Identification of ions and gases
« Reply #8 on: January 01, 2011, 06:20:55 AM »
Ooooh I used to know this. There's a soluble compound that changes color in the presence of different halogen ions but I can't remember it! I *think* it's AgNO3 or some other silver-based salt.

@Evaldas, that's what I was thinking. I don't think seawater would behave the same way as the tincture though. If it does... I am throwing out my Lugol's solution  ;D

But we said that it's not AgNO3, because "other than displacement".

Offline vmelkon

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Re: Identification of ions and gases
« Reply #9 on: January 01, 2011, 04:26:06 PM »
Sea water doesn't contain much iodide ions. How could a visual chemical test show it? Most of it is chloride and to some minor extent, sulfate, some bromide, some nitrate, some borate.
It probably requires mass spectrometry which is much more sensitive and precise.

Offline Twigg

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Re: Identification of ions and gases
« Reply #10 on: January 01, 2011, 04:57:21 PM »
Vmelkon: point taken. I think you're on to the right answer. Mass spectrometry would give the identity of iodide ions by their unique mass-to-charge ratio.

Offline sci994

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Re: Identification of ions and gases
« Reply #11 on: January 01, 2011, 05:18:48 PM »
After adding HNO3 and Pb(No3)3 a yellow ptt is formed (PbI2)
Reaction:
Pb(NO3)2 (aq) + 2KI (aq)  :rarrow: PbI2 (s) + 2KNO3

Pb2++2I- :rarrow: PbI2

Offline cliverlong

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Re: Identification of ions and gases
« Reply #12 on: January 02, 2011, 04:36:57 AM »
Iodine / thiosulphate clock reaction, Hydrogen peroxide variation?

http://en.wikipedia.org/wiki/Iodine_clock_reaction

Offline Evaldas

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Re: Identification of ions and gases
« Reply #13 on: January 02, 2011, 06:05:10 AM »
After adding HNO3 and Pb(No3)3 a yellow ptt is formed (PbI2)
Reaction:
Pb(NO3)2 (aq) + 2KI (aq)  :rarrow: PbI2 (s) + 2KNO3

Pb2++2I- :rarrow: PbI2
Other than displacement!
Plus there are other halogen compounds in sea water, like NaCl which would also react with the nitrate and form a precipitate.

Offline alicia_tan2113

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Re: Identification of ions and gases
« Reply #14 on: January 02, 2011, 10:59:29 PM »
 ;D you guys get my pain xD

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