# time of flight chemistry a level

I'm trying to go through time of flight calculations, i understand the equations apart from how to calculate the mass value in ke=mv^2. the mark schemes sometimes do the mr/avogadros or (mr x 10^-3) x avogadros or somethign along the lines of that. can someone help me understand
By definition, in one mole of a substance, there are 6.022 x10^23 atoms/ions/molecules of that substance.
The Mr of a substance represents the weight of 1 mole of a substance, in grams.
e.g. 1 mole of copper weighs 63.5g

Therefore to find the weight of a single atom/ion/molecule of the substance, you will need to divide the Mr by Avogadro's constant.
e.g. 1 copper atom/ion weighs 63.5/(6.022 x10^23) = 1.05 x10^-22g

This will give you the weight in g, so often you will further be required to divide by 10^3 to convert to kg, as you have mentioned.
e.g. 1 copper atom/ion weighs (1.05 x10^-22)/10^3 = 1.05 x10^-25

Hope this helps
Original post by Methene
By definition, in one mole of a substance, there are 6.022 x10^23 atoms/ions/molecules of that substance.
The Mr of a substance represents the weight of 1 mole of a substance, in grams.
e.g. 1 mole of copper weighs 63.5g
Therefore to find the weight of a single atom/ion/molecule of the substance, you will need to divide the Mr by Avogadro's constant.
e.g. 1 copper atom/ion weighs 63.5/(6.022 x10^23) = 1.05 x10^-22g
This will give you the weight in g, so often you will further be required to divide by 10^3 to convert to kg, as you have mentioned.
e.g. 1 copper atom/ion weighs (1.05 x10^-22)/10^3 = 1.05 x10^-25
Hope this helps

thank you sm
Original post by user1234512345
thank you sm

Happy to help!