Time of flight of mass spectrometry

My teacher says that we don’t need to learn this yet, however I am really confused about how it can be solved. The question is: all particles have the same kinetic energy (=1/2 mv2, where m=mass of the particle and v= velocity) and the velocity of the particles is given by v=d/t (where d=distance travelled and t= time taken). If the time of flight of a 54Cr+ ion is 1.486 x 10-5 seconds, calculate the time of flight of a 50Cr+ ion. Give your answer to the appropriate sig figs. Any help would be appreciated

Reply 1

johnthebaptist27

13

So we have three equations here we can use, the two you said and the definition of the mole.

We need to find the mass of a single ion of 54Cr+ ion, can you think how to do this using the definition of the mole?

We can then get an expression for the velocity of the of the ion in terms of Ek, and use this to find the length of the TOF spectrometer in terms of Ek.
Then, doing a similar thing for the other ion, do you think you could find the time of flight? Tip: Ek cancels at some point.

If you can spot it, you can do this without finding the exact mass of a molecule, but this may be easier after you have done it once.

Reply 2

username5412718

OP

7

Original post by johnthebaptist27

So we have three equations here we can use, the two you said and the definition of the mole.

We need to find the mass of a single ion of 54Cr+ ion, can you think how to do this using the definition of the mole?

We can then get an expression for the velocity of the of the ion in terms of Ek, and use this to find the length of the TOF spectrometer in terms of Ek.
Then, doing a similar thing for the other ion, do you think you could find the time of flight? Tip: Ek cancels at some point.

If you can spot it, you can do this without finding the exact mass of a molecule, but this may be easier after you have done it once.

Thank you, this really helps!

Time of flight of mass spectrometry

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