Chem. A-Level: urgent! Watch

Cliqueatthedisco
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I have been trying to find help but the information is not available in any of my textbooks...please help!
P.S: if you are able to answer, could you include an explanation as to why or how certain things are done to achieve that answer? My aim is to understand, not just copy someone !!

The Mass Spectrum of Butonane shows it's main peak at m/z 72. It also has a snall signal at m/z 73.

a) Which ionisation technique is likely to have been used?
b) What is the relative formula mass of this compound? (To my ubderstanding to find the RFM, I need the abundance, but that info. Is not given??)
c) Give two reasons for the peak at m/z 73.


And please can somebody confirm I answered this corectly?
d) There would also be tiny peaks at m/z 74,75, ect. Explain why some ions with these m/z values may be formed but why their signals may be too small to he seen.

I wrote: Tiny peaks are due to unstable molecules, and have low abundance.
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ChemistryWebsite
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Rather than just give the answers, which you don't really want anyway - you just want help to learn
By the way, you presumably are refering to butanone?

A) the answer to this will be in the introduction to mass spectroscopy part of any relevant text book. The answer is general to mass spectroscopy and not specific to butanone.

B) The abundance of what? I think you may be getting confused with earlier learning about analysing pure elements for their isotope relative abundancies.
Now, what is the main MS peak when analysing a spectrum? What does "molecular ion" mean to you?

C) and D) The carbon, hydrogen and oxygen present may exist as more than one isostope. This could lead to different masses, therefore different peaks.
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Cliqueatthedisco
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Thank you for pointing out the spelling mistake! And thank you for explaining everything so clearly, it made me realise I already understood some of these concepts, just needed to practice them in question form I guess.
I have, I think, figured the answers out.

A) Electropray Ionisation (It was not in my textbook though /: quiet concerning)

and

B) 73?

and thank you so much again, it really helps!
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ChemistryWebsite
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B is actually 72.
The smaller peak at 73 is due to some molecules having a higher mass isotope present (such as a deuterium or a C-13). Always ignore that very small peak beyond the molecular ion peak when deciding RFM
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Cliqueatthedisco
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ohhh okay that actualy makes a lot of sense...I will be sure to note it down and remember! thank you
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