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Topic: second marathon problem (much more difficult)  (Read 15914 times)

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Offline Borek

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Re: second marathon problem (much more difficult)
« Reply #15 on: September 07, 2009, 06:13:36 PM »
is this final reaction when it says you take the filtrate from the original reaction, dilute it with water, then titrate it with potassium permanganate solution, and the products are manganese (IV) oxide and carbonate ion?

MSO4 (where M is the metal) + KMnO4 -> MnO2 + CO3-?

if so, where is the carbon coming from in the products?

What is filtrate? What was precipitated?
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Offline sapphiregirl

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Re: second marathon problem (much more difficult)
« Reply #16 on: September 07, 2009, 06:52:28 PM »
these are the reactions that i have:

M(CHO2)2 + Na2SO4 -> 2NaCHO2 + MSO4 (this is from the first paragraph)

Na2C2O4 + H2SO4 + KMnO4 -> Mn2+ + 2CO2 (this is from the second paragraph)

MSO4 + MnO41- -> MnO2 + CO31- (this is from the third paragraph)

i don't know where to go from here.

Offline Borek

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Re: second marathon problem (much more difficult)
« Reply #17 on: September 08, 2009, 02:41:44 AM »
M(CHO2)2 + Na2SO4 -> 2NaCHO2 + MSO4 (this is from the first paragraph)

OK

Quote
Na2C2O4 + H2SO4 + KMnO4 -> Mn2+ + 2CO2 (this is from the second paragraph)

OK

Quote
MSO4 + MnO41- -> MnO2 + CO31- (this is from the third paragraph)

This is wrong. I have already signalled why, but instead of trying to understand the hints you prefer to write

Quote
i don't know where to go from here.

You won't get far this way. When you are thinking you are doing fine. Yes, you can.
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Offline sapphiregirl

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Re: second marathon problem (much more difficult)
« Reply #18 on: September 08, 2009, 07:17:21 PM »
i thought the precipitate and the filtrate was the same which is why i was confused.

anyway, the filtrate is NaCHO2 so the third formula is NaCHO2 + MnO41- -> MnO2 + CO31-, right?

Offline Borek

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Re: second marathon problem (much more difficult)
« Reply #19 on: September 09, 2009, 02:49:17 AM »
anyway, the filtrate is NaCHO2 so the third formula is NaCHO2 + MnO41- -> MnO2 + CO31-, right?

Something like that - probably ignoring Na+ (spectator) and writing product as CO2 it will be easier to balance reaction equation.

Observe your chanrges - no such thing as CO3-
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Offline sapphiregirl

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Re: second marathon problem (much more difficult)
« Reply #20 on: September 09, 2009, 07:39:57 AM »
The principal products of the reaction are carbonate ion and manganese (IV) oxide.

straight from the problem. isn't the carbonate ion CO3 (charge of 1-)?

Offline Borek

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Re: second marathon problem (much more difficult)
« Reply #21 on: September 09, 2009, 07:44:53 AM »
Carbonate is CO32-.

For the stoichiometry of permanganate/formate reaction it doesn't matter if the product is CO2 or CO32- - in both cases molar ratio of permanganate and formate is identical, and that's what is important for the final answer. IMHO reaction will be easier to balance with CO2 listed as a product.

No idea who will check your work and how - nitpicker may argue that you have not followed the problem verbatim.
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Offline sapphiregirl

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Re: second marathon problem (much more difficult)
« Reply #22 on: September 09, 2009, 07:48:07 PM »
thank you for all your help. i just handed in my homework today to the teacher so we'll see what happens. thanks again.

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