In a particular spectrometer, doubly ionised C (atomic no. 6 mass no. 12) and singly ionised Li (atomic no. 3 mass no. 6) atoms are(adsbygoogle = window.adsbygoogle || []).push({});

detected. The ratio of the path radii is 1.00252, the Li having the larger value. The

fields are constant.

a)Find the mass of the lithium ion.

Okay so i have already figured out that i have to use the equation:

R=mV/qB (where m = mass, V = velocity, q= charge on electron, R= radius made by the ion and B= magnetic field strength)

I also have the equation:

q(1)R(1)/m(1) = q(2)R(2)/m(2)

(where the numbers in brackets are meant to be subscript)

This equation comes from knowing the value of V/B is constant.

so q(1)= 1.6x10^-19

q(2)= 3.2x10^-19

R(1)/R(2) = 1.00252

(R(1) being the radius of the lithium ion since it is stated to be the largest value)

This takes me to:

m(1)/m(2) = 0.50126

And this is where i get stuck! I cant see a way of doing this question without knowing the mass of carbon. I emailed my lecturer but all he said was 'The mass of carbon is implicit'.

Can anyone help? Thanks! :)

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# Homework Help: Bainbridge Mass Spectrometer - Finding the mass of ions

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