Problem: The natural abundance of 3 He is 0.000137 %.Based on your answer for part (b), what would need to be the precision of a mass spectrometer that is able to differentiate between peaks that are due to 3He+ and 3H+ ?a) 1 × 10− 21 gb)  1 × 10−21 kgc) 1 × 10−27 kgd) 1 × 10−24 ge) 1 × 10−27 g

FREE Expert Solution

From Part b, an atom of 3H is more massive than an atom of 3He.


  • mass 3He: 2p, 2e, 1n

massHe3=2(1.0073 amu)+2(0.000549 amu)+1(1.0087 amu)

mass 3He = 3.02439 amu

  • mass 3H: 1p, 1e, 2n

massH3=1(1.0073 amu)+1(0.000549 amu)+2(1.0087 amu)
mass 3H = 3.0252 amu


m=mass H3-He3=(3.0252-3.02439)amu

= 8.02 x 10-4 amu


Precision of mass spectrometer:

  • 6.022 x 1023 amu = 1 g
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Problem Details

The natural abundance of 3 He is 0.000137 %.

Based on your answer for part (b), what would need to be the precision of a mass spectrometer that is able to differentiate between peaks that are due to 3He+ and 3H+ ?


a) 1 × 10− 21 g

b)  1 × 10−21 kg

c) 1 × 10−27 kg

d) 1 × 10−24 g

e) 1 × 10−27 g


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