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Topic: Percent Composition Lab Procedure  (Read 13973 times)

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Offline AWK

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Re:Percent Composition Lab Procedure
« Reply #15 on: March 23, 2006, 04:56:06 AM »
Just add an excess of concentrated HNO3, even may be diluted, but reaction proceeds slower. The excess means in this case about 1.5 to 2 ml of concentrated HNO3 per 1 gram of an alloy.
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rach1023

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Re:Percent Composition Lab Procedure
« Reply #16 on: March 29, 2006, 01:15:55 AM »
This wouldn't happen to be an extra credit problem given in chem lab at the University of Texas, would it?  Because I definitely have the same one.  Thanks for the help guys!
« Last Edit: March 29, 2006, 01:31:14 AM by rach1023 »

onpeakhill

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Re:Percent Composition Lab Procedure
« Reply #17 on: March 30, 2006, 02:26:38 PM »
Alloy Ag2Cu does not react with NaCl

Start from dissolving of both metals (weighted sample of an alloy) in concentrated HNO3
Then precipitate AgCl and weight it after drying.
These data will be sufficient to calculate mass percent composition of this alloy

i don't see how you get AgCl if you said Ag2Cu does not react with NaCl?

onpeakhill

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Re:Percent Composition Lab Procedure
« Reply #18 on: March 30, 2006, 02:29:52 PM »
Ag(s) + 2HNO3 = AgNO3 + NO2(g) + H2O
Cu(s) + 4HNO3 = Cu(NO3)2 + 2NO2(g) + 2H2O

basically we are dissolving the alloy in the concentrated nitric acid
precipitating it and drying it
weighing it
and based on these equations
we find mass of Ag and Cu?
then find the mass percent composition of both?
i still don't see how (AgCl) was involved.

Offline Borek

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Re:Percent Composition Lab Procedure
« Reply #19 on: March 30, 2006, 02:34:31 PM »
AgNO3(aq) + NaCl(aq) -> NaNO3(aq) + AgCl(s)

or, in net ionic form

Ag+ + Cl- -> AgCl(s)

NaCl is a source of Cl- that will precipitate AgCl.
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onpeakhill

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Re:Percent Composition Lab Procedure
« Reply #20 on: March 30, 2006, 05:21:46 PM »
Alloy Ag2Cu does not react with NaCl

Start from dissolving of both metals (weighted sample of an alloy) in concentrated HNO3
Then precipitate AgCl and weight it after drying.
These data will be sufficient to calculate mass percent composition of this alloy

By calculating this,
i would get the % composition of the silver?
Like so (mass of Ag/mass of AgCl x 100) ?

Offline Borek

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Re:Percent Composition Lab Procedure
« Reply #21 on: March 31, 2006, 07:53:10 AM »
By calculating this,
i would get the % composition of the silver?
Like so (mass of Ag/mass of AgCl x 100) ?

Exactly. You dissolve alloy, precipitate AgCl and filtrate it - at this moment you have solid that you can weight (after drying), mass of this solid allows calculation of mass of Ag - and bingo, everything is done.
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