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Stereoisomer

Observations of Redox/Precipitation reactions

How can I tell what the color of a random chemical in a test without looking at it?It sounds really silly but that's what we have to do.


Here is a Redox Reaction from a textbook:

Pb2+(aq) + Fe(s) --------------> Pb(s) + Fe2+ (aq)
Observation: Solution stays colorless, dark gray shiny crystals formed
Why does the solution remain colorless? Shouldn't be green as Fe2+ is always green??

oh and another one:

2Fe3+(aq) + 2I- (aq) --------> 2Fe2+(aq) +I2(aq)
Observation: Solution changes from yellow to deep red brown.
OK so where did the yellow came from? (I thought all Fe3+ are orange brown) and how come it turned red brown? I know the Iodine turns brown and the Fe2+ SHOULD turn green but they don't make red brown do they?

Is there a way of knowing in exact?
thanks!!!

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[quote name='MistyRose' post='25684' date='Sep 29 2008, 01:20 AM']How can I tell what the color of a random chemical in a test without looking at it?It sounds really silly but that's what we have to do.

Is there a way of knowing in exact?[/quote]

Oh yes, that sounds silly. Observations cannot be determined before being observed... I mean, elsewise, it would not make any sense of observing. So no, there is no way of exactly knowing of what [i]should[/i] be, before you, yourself, observe the reaction in detail and express your interpretation in form of text. You may think that the precipitation is green, while I, on the other hand, think it is grey. Observations are thus highly individual.

Though, I know that there are some 'rules' to follow (this and this forms a prec. etc.), but they are only for calculation and hypothesis.

Sorry for not answering your question. :P

Complain.

Edit: My knowledge is limited :yahoo: , just started with Chemistry HL.

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you have to have studies the transition elements bit of the periodicity. learn what each transition metal's colour is in solution and you'll basically figure it out that way. It's all in the periodicity chapter, you basically need to memorize the colour changes and what not...

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[quote name='~Lc~' post='26587' date='Oct 11 2008, 12:08 AM']you have to have studies the transition elements bit of the periodicity. learn what each transition metal's colour is in solution and you'll basically figure it out that way. It's all in the periodicity chapter, you basically need to memorize the colour changes and what not...[/quote]

Oh yes, this sounds more correct.

:yahoo: :P

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