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Topic: Problem of the week - 29/04/2013  (Read 31130 times)

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Offline Borek

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Problem of the week - 29/04/2013
« on: April 29, 2013, 05:20:52 PM »
1.000 g of a roasted salt decomposes producing three oxides - 0.878 g of a solid one, 0.0354 g of a liquid one and 0.0866 g of a gaseous one (at STP).

Determine the salt identity.
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Offline Rutherford

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Re: Problem of the week - 29/04/2013
« Reply #1 on: April 30, 2013, 01:17:36 PM »
I got Pb(OH)2·PbCO3 or (PbOH)2CO3, not quite sure  :-\.

Offline Big-Daddy

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Re: Problem of the week - 29/04/2013
« Reply #2 on: April 30, 2013, 01:41:04 PM »
(PbOH)2CO3,

Surely this can't exist ... That would mean the (PbOH)+ ion exists which I doubt.

Offline Rutherford

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Re: Problem of the week - 29/04/2013
« Reply #3 on: April 30, 2013, 02:35:45 PM »
Okay, then maybe the first one.

Offline Big-Daddy

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Re: Problem of the week - 29/04/2013
« Reply #4 on: April 30, 2013, 02:38:44 PM »
Borek when you say oxides do you just mean the salt contains oxygen in some form, or specifically the O2- ion? (Or can you not tell us?)

Offline Borek

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Re: Problem of the week - 29/04/2013
« Reply #5 on: April 30, 2013, 03:28:08 PM »
Borek when you say oxides do you just mean the salt contains oxygen in some form, or specifically the O2- ion? (Or can you not tell us?)

No idea what you are asking about. Have you seen gaseous oxide containing O2-?
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Offline Big-Daddy

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Re: Problem of the week - 29/04/2013
« Reply #6 on: April 30, 2013, 04:27:16 PM »
Borek when you say oxides do you just mean the salt contains oxygen in some form, or specifically the O2- ion? (Or can you not tell us?)

No idea what you are asking about. Have you seen gaseous oxide containing O2-?

No, but then Raderford is suggesting a carbonate, which I would not normally class as an oxide. So by oxide you mean any salt containing O somewhere?

Offline Borek

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Re: Problem of the week - 29/04/2013
« Reply #7 on: April 30, 2013, 04:42:38 PM »
No, but then Raderford is suggesting a carbonate, which I would not normally class as an oxide. So by oxide you mean any salt containing O somewhere?

Have you read the question?
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Offline Big-Daddy

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Re: Problem of the week - 29/04/2013
« Reply #8 on: April 30, 2013, 05:20:20 PM »
No, but then Raderford is suggesting a carbonate, which I would not normally class as an oxide. So by oxide you mean any salt containing O somewhere?

Have you read the question?

 :-[ That was stupid of me.

Offline delta609

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Re: Problem of the week - 29/04/2013
« Reply #9 on: May 01, 2013, 08:17:58 PM »
TlHCO3
« Last Edit: May 01, 2013, 10:04:41 PM by delta609 »

Offline delta609

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Re: Problem of the week - 29/04/2013
« Reply #10 on: May 01, 2013, 08:18:29 PM »
 I didn't get the exact amounts you have posted, but very close. 

2TlHCO3  :rarrow: Tl2CO3 + CO2 + H2O
Tl

Tl2CO3 = .883g
CO2 = .083g
H2O = .034g
« Last Edit: May 01, 2013, 10:05:16 PM by delta609 »

Offline Borek

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Re: Problem of the week - 29/04/2013
« Reply #11 on: May 02, 2013, 03:00:08 AM »
Tl2CO3 is not an oxide.
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Offline delta609

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Re: Problem of the week - 29/04/2013
« Reply #12 on: May 02, 2013, 01:12:43 PM »
Pb2(OH)2CO3

Pb2(OH)2CO3  :rarrow: 2PbO + CO2 + H2O

numbers are spot on this time.

Offline Borek

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Re: Problem of the week - 29/04/2013
« Reply #13 on: May 02, 2013, 02:29:04 PM »
Raderford was first:

I got Pb(OH)2·PbCO3 or (PbOH)2CO3, not quite sure  :-\.

No matter how you write it, this is the intended answer.

And I should slap myself again, as I have not checked details. Problem was used in a chemistry competition, and after solving and checking that the numbers are OK I assumed the compound is just a basic lead carbonate. Turns out it is not - so called white lead has a slightly different formula (2PbCO3·Pb(OH)2). It doesn't mean Pb(OH)2·PbCO3 doesn't exist, as there are several similar compounds, but I prefer problems with the obviously existing real solutions.
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Offline blaisem

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Re: Problem of the week - 29/04/2013
« Reply #14 on: May 03, 2013, 08:33:25 AM »
Would anyone mind providing a link or a keyword for google where I can read how a problem like this is approached/solved?

Thank you

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