Electrogeek
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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?
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Electrogeek
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I have tried the answer again, would I be right in saying that the distance is about 2.1 meters?
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charco
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(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.

Avogadro constant = 6.022x10^23 "

Can someone please help or give a rough outline of what steps I need to do?
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
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Electrogeek
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Thanks! I'm glad that I had the right answer.
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charco
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(Original post by Electrogeek)
Thanks! I'm glad that I had the right answer.
It's more physics than chemistry IMHO
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Barbie1998
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(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?
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charco
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(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.
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Barbie1998
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(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!
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derpz
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(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
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derpz
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(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
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charco
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(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.
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Pigster
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When oh when oh when will physics admit that they got the unit of mass wrong and re-write all their textbooks?
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charco
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(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 ...
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JiaS
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what paper is this question from??
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Electrogeek
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(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. 😊
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JiaS
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(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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olami
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what exact paper is this question from
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