dyfugikholjp
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A molecule Q is ionised By electron impact in A TOF mass spectrometer the Q+ ion Has a kinetic energy of 2.09 x 10-15 J.This ion takes 1.23 x 10-5 s to reach the detector The length of the flight tube is 1.50 m
Calculate the relative molecular mass of Q
K.E. = 1/2 m v2
Where the mass=mass(kg) and v=speed (m s -1 )
The avagardo constant L =6.022x1023 mol-1
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dyfugikholjp
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this is iy
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Joinedup
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what are you confused about? what have you tried?

do you understand how a TOF mass spectrometer works?
can you calculate the mass of the ion in SI units (kg)?
can you convert from kg to grams?
do you understand that 'relative atomic mass' means 'mass expressed in atomic mass units
can you convert between g and amu (using Avogadro's constant)?
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replaythat
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(Original post by dyfugikholjp)
A molecule Q is ionised By electron impact in A TOF mass spectrometer the Q+ ion Has a kinetic energy of 2.09 x 10-15 J.This ion takes 1.23 x 10-5 s to reach the detector The length of the flight tube is 1.50 m
Calculate the relative molecular mass of Q
K.E. = 1/2 m v2
Where the mass=mass(kg) and v=speed (m s -1 )
The avagardo constant L =6.022x1023 mol-1
did you ever find the answer to this
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Hayatleung
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#5
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(Original post by replaythat)
did you ever find the answer to this
169
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Hayatleung
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(Original post by dyfugikholjp)
A molecule Q is ionised By electron impact in A TOF mass spectrometer the Q+ ion Has a kinetic energy of 2.09 x 10-15 J.This ion takes 1.23 x 10-5 s to reach the detector The length of the flight tube is 1.50 m
Calculate the relative molecular mass of Q
K.E. = 1/2 m v2
Where the mass=mass(kg) and v=speed (m s -1 )
The avagardo constant L =6.022x1023 mol-1
m = (2KE/v^2)
((2 x 2.09x10^-15)/((1.5/1.23x10^-5)^2)
= 2.81x10^-25kg = 2.81x10^-22g
Mr = g/mol
therefore
mr = mass/L
Mr = 2.81x10^-22g / 6.022x10^23
Mr = 169.256
Only 3 sig figs needed as lowest amount of sig figs in the questions
therefore Mr = 169.
BOOM!
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Abinayan_K
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(Original post by Hayatleung)
m = (2KE/v^2)
((2 x 2.09x10^-15)/((1.5/1.23x10^-5)^2)
= 2.81x10^-25kg = 2.81x10^-22g
Mr = g/mol
therefore
mr = mass/L
Mr = 2.81x10^-22g / 6.022x10^23
Mr = 169.256
Only 3 sig figs needed as lowest amount of sig figs in the questions
therefore Mr = 169.
BOOM!
shouldn't it be (2.81 x 10^-22) MULTIPLIED BY (6.022 x 10^23) to give 169 as the relative molecular mass?
(2.81x10^-22) / (6.022x10^23) gives (4.67 x 10^-46), not 169
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FionaT27
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(Original post by Abinayan_K)
shouldn't it be (2.81 x 10^-22) MULTIPLIED BY (6.022 x 10^23) to give 169 as the relative molecular mass?
(2.81x10^-22) / (6.022x10^23) gives (4.67 x 10^-46), not 169
Could you explain why we multiply by Avogadros?
Last edited by FionaT27; 4 weeks ago
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Dominininc
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The formula is Mr = g/number of moles.

Because we have 1 ion, the number of moles is 1/avogardos constant

Dividing by 1/avocado is the same as multiplying by Avocado/1 which is the same as multiplying by avocado. So you can multiply by avocado in the case where you only have one number of something.

Therefore Hayatleung made a typo by not putting 1/avocado and Abinayan_K has corrected them but did not provide the 1/avocado part and inb order to make the maths work suggested multiplication.
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FionaT27
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Thanks for replying but I still don’t understand why it would be 1/Avogadros?
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Dominininc
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1/avogadro is athe quantity of how many moles we have.

we have 1 ion and there a 6.02*1023 ions in a mole so we have 1/avogadro moles.

using the eqn

Mr=g/no. mol
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