TOF mass spec

Hi everyone,

I've been given this question, and I have a answer which is definitely wrong:

"In a TOF mass spectrometer, ions are accelerated to the same kinetic energy. Each ( 25Mg+ ) ion is accelerated to a kinetic energy of 4.52x10^-16 J, and the time of flight is 1.44x10^-5 seconds.

Calculate the distance travelled, in meters, in the TOF drift region.

Avogadro constant = 6.022x10^23 "

Can someone please help or give a rough outline of what steps I need to do?

Thanks! I'm glad that I had the right answer.

Kinetic energy = 1/2mv²

mass = 25/L = 4.15 x 10^-26 kg

2 x 4.52 x 10^-16/4.15 x 10^-26 = v²

v = 147591 ms^-1

TOF = 1.44x10^-5 s

distance = vt = 2.13 m

Could you explain how you calculates the mass please?

You are told that it is a ²⁵Mg+ ion. The '25' represents the relative mass on a scale in which an atom of the ¹²C isotope = 12.00000.

Hence an Avogadro number of atoms
of ²⁵Mg have a mass of 25g

To find the mass in kg of one atom you must divide by 6.0223 x 10²³ and then by 1000.

Kinetic energy = 1/2mv²

mass = 25/L = 4.15 x 10^-26 kg

2 x 4.52 x 10^-16/4.15 x 10^-26 = v²

v = 147591 ms^-1

TOF = 1.44x10^-5 s

distance = vt = 2.13 m

So Mass in grams is RFM/avogadro constant

Then divide by 1000 again cos it's in kg.

Could you explain what formula you used to get the mass of the molecule? Thats the only part i do not understand

When oh when oh when will physics admit that they got the unit of mass wrong and re-write all their textbooks?

what paper is this question from??

This is one of the specimen papers from AQA for this year's new A level specification. 😊