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Topic: Problem of the week - 14/01/2013  (Read 17072 times)

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Offline Borek

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Problem of the week - 14/01/2013
« on: January 14, 2013, 12:17:32 PM »
In 1966, while researching reactions between NO and a simple substance A, Neil Bartlett found two products – the main one, B, and an interesting side product C. Mass spectrum of the compound C contained peaks listed in the attachment.

C survived heating up to 260 °C and was stable in the presence of concentrated alkaline solutions. Mixed with hydrogen it exploded at 170 °C. Reaction with iodides produced 1.5 mmol I2 for every mmol of C (NO evolved during this reaction). C reacted with the hydrofluoric acid substantially increasing conductivity of the solution, and after further addition of BF3 two crystalline adducts were produced – one (D) contained 6.98% boron and the other (E) 9.71% boron.

Give formulas of all substances A to E.

(Note: generally speaking it is not possible to deduct formula for B from the information given, so if you have no idea  what it can be - don't worry.)
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Offline DrCMS

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Re: Problem of the week - 14/01/2013
« Reply #1 on: January 14, 2013, 06:29:55 PM »
I think Jack Passmore knows all the answers.

Offline Schrödinger

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Re: Problem of the week - 14/01/2013
« Reply #2 on: January 15, 2013, 02:54:54 AM »
I'm just going to take a guess at A and C, having done nothing other than look at the mass spec :P

N = syhbevar
P = ABS2 ?
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Offline Borek

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Re: Problem of the week - 14/01/2013
« Reply #3 on: January 18, 2013, 05:01:28 AM »
You are on the right track, but not entirely correct.

Actually you felt in the same trap I did when first approaching this problem.
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Offline Borek

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Re: Problem of the week - 14/01/2013
« Reply #4 on: January 21, 2013, 05:42:19 AM »
Extending the deadline for another week...
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Offline DrCMS

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Re: Problem of the week - 14/01/2013
« Reply #5 on: January 21, 2013, 05:55:04 AM »
I found Jack Passmore's PhD thesis that describes this work but he only describes the characterisation of one product from C with HF + BF3 and I get a slightly different %B (9.26) for the material he found?

Offline Borek

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Re: Problem of the week - 14/01/2013
« Reply #6 on: January 22, 2013, 08:55:56 AM »
Hard to comment - I am relying on the question prepared by someone else (the answer given looks reasonable). I have checked that the numbers I posted reflect the formulas expected, so there is no simple mistake or typo in what I posted.
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Offline DrCMS

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Re: Problem of the week - 14/01/2013
« Reply #7 on: January 22, 2013, 02:34:38 PM »
A = F
B = NOF or NO2
C = NOF3
D = ??
E = NOBF4 but I calculate it to be 9.26%B

Offline Borek

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Re: Problem of the week - 14/01/2013
« Reply #8 on: January 24, 2013, 06:35:50 AM »
Answer key gives B as NOF.

NOBF4 would be made from NOF (B) and not NOF3 (C).
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Offline DrCMS

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Re: Problem of the week - 14/01/2013
« Reply #9 on: January 24, 2013, 02:23:47 PM »
Answer key gives B as NOF.

His PhD thesis (https://circle.ubc.ca/bitstream/handle/2429/37267/UBC_1968_A1%20P375.pdf?sequence=1) lists both NOF and NO2 as the major products from NO + F2

NOBF4 would be made from NOF (B) and not NOF3 (C).

No his PhD quite clearly states the reaction of NOF3 with HF and BF3 was done to try to make HNOF3BF4 but they could find no evidence it was formed but that the IR spectra of the solid was identical to NOBF4

Offline Borek

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Re: Problem of the week - 14/01/2013
« Reply #10 on: January 25, 2013, 06:53:27 AM »
No his PhD quite clearly states the reaction of NOF3 with HF and BF3 was done to try to make HNOF3BF4 but they could find no evidence it was formed but that the IR spectra of the solid was identical to NOBF4

Sadly, you are right. I had troubles getting the document, but eventually I managed to download it and have it here. Page 77:

Quote
2.3.3.(d) HF + BF3 + ONF3

It has been shown that boron trifluoride does not react with ONF3 at ambient temperatures and pressures, but it was possible that the acid HBF4 might protonate ONF3 and form the salt HONF3BF4.

Equal quantities of BF3 and ONF3 were condensed into an infrared cell and the excess anhydrous HF was added. The infrared spectrum was taken and all three components to be present.

The experiment was repeated in a a Kel-F trap. The gases were added to the trap and some solid was seen to form. The volatile gases were removed into the infrared cell and a spectrum showed them to be HF, ONF3 and BF3. The X-ray diffraction pattern of the solid was complex and did not correspond to NOBF4 or to NO2BF4. The solid partly dissolved in anhydrous HF, the 19F n.m.r. of which revealed the presence of BF4- ion. The infrared spectrum of the solid was identical to NOBF4.

So it looks like someone "invented" the chemistry behind the question. Sigh.
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Offline DrCMS

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Re: Problem of the week - 14/01/2013
« Reply #11 on: January 25, 2013, 07:20:09 AM »
So it looks like someone "invented" the chemistry behind the question. Sigh.

It might be that later work done by another student of Neil Barlett got some different results using different conditions to Jack Passmore?

I found the info I did based on the date and name etc but I do not have access to the published papers.

What were the "correct" answers you had?


Offline Borek

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Re: Problem of the week - 14/01/2013
« Reply #12 on: January 25, 2013, 07:30:07 AM »
A - F2
B - NOF
C - NOF3
D - NOF3·BF3
E - NOF3·2BF3
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