Mass spec

http://filestore.aqa.org.uk/subjects/AQA-CHEM1-QP-JUN15.PDF

explain to me question 2e i don't understand why the answer isn't fragmentation

I might be wrong but Tellurium is an element not a compound. I don't think you can make it undergo fragmentation because you're not splitting it into ions, it's just a single element. In this case, you might be making it into an ion

Oh ok so it's not fragmentation so what's the right answer and why?

I might be wrong but Tellurium is an element not a compound. I don't think you can make it undergo fragmentation because you're not splitting it into ions, it's just a single element. In this case, you might be making it into an ion

the m/z at 64 is due to the 128Te2+ ion

How did that happen? Did it disassociate or something?

the m/z at 64 is due to the 128Te2+ ion

an atom lost two electrons during the electron bombardment (it happens sometimes)

i don't understand where this comes from


I don't understand ? what's happening, it seems to me there's just random links everywhere ^-^

i can see halving 128 gives 64
i don't even know if Te is a diatomic molecule or not
i have no idea where 2 electrons lost comes from

Metals don't normally form diatomics (they can, it's just usually in specific circumstances). In this kind of question just consider individual atoms being bombarded with electrons.

So mass spec measures the mass/charge ratio, what happens if two electrons are removed, not one?

So how can you have 64 as an m/z then???
Where do electrons come into this?

wait so mass/charge ratio

so if you got a mass of 128 and you lose 2 electrons then huh??? i don't understand

So how can you have 64 as an m/z then???
Where do electrons come into this?

wait so mass/charge ratio

so if you got a mass of 128 and you lose 2 electrons then huh??? i don't understand

This type of mass spec works by ionising the species (in this case atoms of Te) you want to find the mass for, then accelerating them. This gives you the amount of mass per unit charge of the ionised species.

One of the most common isotopes of Te is Te-128. So when you ionise the Te to Te⁺, you get a reading at 128 (as the mass-to-charge ratio is 128/1). However if you ionise the Te to Te²⁺, you get a reading at 64 (as the mass-to-charge ratio is 128/2=64).

The x-axis scale is mass/charge (m/z)

m/z means mass to charge RATIO

If the mass is 128 and the charge is 2+ then the ratio = 128/2 = 64

During the electron bombardment process occasionally an atom loses two electrons and develops a double positive charge = 2+

So its mass to charge ratio = 128/2 = 64

I can't say it in simpler terms!

oh i see right i understand now

so what if the ion is Te¹⁺?? 128/1 is still 1 so how would i know any differe....

good point that's me being silly

That's TOF mass spec right? not electron impact

In ALL forms of mess spectrometry the species must be ionised first. Otherwise you could not accelerate them ...