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AS aqa chem help please asap

so ive been doing a lot of questions and there are a lot of questions like
"State how krypton is ionised in the mass spectrometer" and the mark scheme is specific about either electrospray or electron impact but how am i supposed to know which type of ionisation it would be?
Original post by jennaa21
so ive been doing a lot of questions and there are a lot of questions like
"State how krypton is ionised in the mass spectrometer" and the mark scheme is specific about either electrospray or electron impact but how am i supposed to know which type of ionisation it would be?

Electrospray ionisation is typically used for larger molecules, whereas small molecules and atoms can often be ionised with electron impact.

See here: https://filestore.aqa.org.uk/resources/chemistry/AQA-7404-7405-SG-TOFMS.PDF
Original post by TypicalNerd
Electrospray ionisation is typically used for larger molecules, whereas small molecules and atoms can often be ionised with electron impact.

See here: https://filestore.aqa.org.uk/resources/chemistry/AQA-7404-7405-SG-TOFMS.PDF


oh okay! thank you - but for my example above i thought krypton was a small molecule but the mark scheme says it was ionised via electrospray?
Original post by jennaa21
oh okay! thank you - but for my example above i thought krypton was a small molecule but the mark scheme says it was ionised via electrospray?


Interesting. It is monatomic, but being a noble gas, removing an electron is probably pretty difficult given the first ionisation energies of the noble gases are pretty high.

It’s not immediately obvious imo and I think the MS should have been a little more lenient.
Original post by TypicalNerd
Interesting. It is monatomic, but being a noble gas, removing an electron is probably pretty difficult given the first ionisation energies of the noble gases are pretty high.

It’s not immediately obvious imo and I think the MS should have been a little more lenient.

yeah i wrote about electron impact but i guess that wouldnt be accepted but im just rlly confused now
Original post by TypicalNerd
Interesting. It is monatomic, but being a noble gas, removing an electron is probably pretty difficult given the first ionisation energies of the noble gases are pretty high.

It’s not immediately obvious imo and I think the MS should have been a little more lenient.

wait i think it depends on the Mr, i found this on chemrevise "Electron impact is used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment."
ig Kr has a relatively high Mr so thats why its supposed to be electrospray ionisation
Original post by jennaa21
wait i think it depends on the Mr, i found this on chemrevise "Electron impact is used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment."
ig Kr has a relatively high Mr so thats why its supposed to be electrospray ionisation

It could be, but I don’t believe they actually state anywhere in the course what constitutes a high Mr.

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