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# TOF mass spec

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1. 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.

2. I have tried the answer again, would I be right in saying that the distance is about 2.1 meters?
3. (Original post by Electrogeek)
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.

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
5. (Original post by Electrogeek)
It's more physics than chemistry IMHO
6. (Original post by charco)
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?
7. (Original post by Barbie1998)
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.
8. (Original post by charco)
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.
Thanks so much!
9. (Original post by charco)
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 what formula you used to get the mass of the molecule? Thats the only part i do not understand
10. So Mass in grams is RFM/avogadro constant

Then divide by 1000 again cos it's in kg.
11. (Original post by AnIndianGuy)
So Mass in grams is RFM/avogadro constant

Then divide by 1000 again cos it's in kg.
Oh right, got it now, I kept getting 4.14x10^-23 because i didnt realise its in kg.

Thanks
12. (Original post by derpz)
Could you explain what formula you used to get the mass of the molecule? Thats the only part i do not understand
divide the mass of one mole of the molecules (the relative mass expressed in grams) by Avogadro's constant.

This gives the mass of 1 molecule in grams.

However, you need the mass in SI units (kg) so you now have to divide by 1000.
13. When oh when oh when will physics admit that they got the unit of mass wrong and re-write all their textbooks?
14. (Original post by Pigster)
When oh when oh when will physics admit that they got the unit of mass wrong and re-write all their textbooks?
The day they realise that electric current flows in the reverse direction ...
15. what paper is this question from??
16. (Original post by JiaS)
what paper is this question from??
This is one of the specimen papers from AQA for this year's new A level specification. 😊
17. (Original post by Electrogeek)
This is one of the specimen papers from AQA for this year's new A level specification. 😊

Oh okay, thanks

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