Diana2212
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#1
Report Thread starter 1 year ago
#1
A sample of bromine was analysed in a time of flight (TOF) mass spectrometer and found to contain two isotopes, 79Br and 81Br

After electron impact ionisation, all of the ions were accelerated to the same kinetic energy (KE) and then travelled through a flight tube that was 0.950 m long.
(a) The 79Br+ ions took 6.69 × 10–4 s to travel through the flight tube.

Calculate the mass, in kg, of one ion of 79Br+

Calculate the time taken for the 81Br+ ions to travel through the same flight tube.

The Avogadro constant, L = 6.022 × 1023 mol–1

KE = mv2 where m = mass (kg) and v = speed (m s–1)

where d = distance (m) and t = time (s)

Mass of one ion of 79Br+ ____________________ kg

Time taken by 81Br+ ions ____________________ s

can somebody explain this question !! How can you find the mass if you don't have KE???
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flowerscat
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#2
Report 1 year ago
#2
1. Find Velocity for Br-79
2. Use this to find KE for Br
3. Use this KE to find Velocity for Br-81
4. Find time

KE for all Br ions is the same - the Time/Velocity differs
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flowerscat
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#3
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#3
Length = 0.950 m
Time for Br 79 = 6.69 × 10–4 s to travel through the flight tube.

Calculate the mass, in kg, of one ion of 79Br+

Mass of 1 mole of Bromine = 79 g = 0.079 kg
Mass of 1 ion = 0.079 divided by 6.022 × 1023 mol–1
Mass of 1 ion = 1.312 x 10-25 kg

Calculate the time taken for the 81Br+ ions to travel through the same flight tube.

KE = 1/2mv2 where m = mass (kg) and v = speed (m s–1), where d = distance (m) and t = time (s)


KE of Br-79 = 1/2 x 1.312 x 10-25 x (0.950 m divided by )
KE of Br-79 = 1.3228 x 10-19

KE of Br-81 = 1.3228 x 10-19

Therefore, Velocity for Br-81 = 1402.23 m/s

Use this to calculate time for Br-81 (using v = d/t) = 6.775 x 10-4


Mass of one ion of 79Br+ _____1.312 x 10-25_______________ kg

Time taken by 81Br+ ions ____6.775 x 10-4________________ s

can somebody explain this question !! How can you find the mass if you don't have KE???
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Diana2212
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#4
Report Thread starter 1 year ago
#4
(Original post by flowerscat)
Length = 0.950 m
Time for Br 79 = 6.69 × 10–4 s to travel through the flight tube.

Calculate the mass, in kg, of one ion of 79Br+

Mass of 1 mole of Bromine = 79 g = 0.079 kg
Mass of 1 ion = 0.079 divided by 6.022 × 1023 mol–1
Mass of 1 ion = 1.312 x 10-25 kg

Calculate the time taken for the 81Br+ ions to travel through the same flight tube.

KE = 1/2mv2 where m = mass (kg) and v = speed (m s–1), where d = distance (m) and t = time (s)


KE of Br-79 = 1/2 x 1.312 x 10-25 x (0.950 m divided by )
KE of Br-79 = 1.3228 x 10-19

KE of Br-81 = 1.3228 x 10-19

Therefore, Velocity for Br-81 = 1402.23 m/s

Use this to calculate time for Br-81 (using v = d/t) = 6.775 x 10-4


Mass of one ion of 79Br+ _____1.312 x 10-25_______________ kg

Time taken by 81Br+ ions ____6.775 x 10-4________________ s

can somebody explain this question !! How can you find the mass if you don't have KE???
ohh that makes so much more sense , thank you so much
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