Use the mass spectrum opposite to calculate the relative atomic mass of neon.
= (20 x 90.89) + (21 x 0.27) + (22 x 8.84)
100
= 20.18
Use the mass spectrum above to calculate the relative atomic mass of barium.
= (132 x 0.15) + (133 x 0.14) + (134 x 3.38) + (135 x 9.19) + (136 x 10.95) + (137 x 15.66) + (138 x 100)
0.15 + 0.14 + 3.38 + 9.19 + 10.95 + 15.66 + 100
=19166.6 /139.47
= 137.42 (to 2dp)
A sample of element M was extracted from a meteorite. The relative abundance of each isotope in a mass spectrum of this sample of M.
| m/z | 64 | 66 | 67 | 68 |
| % | 38.9 | 27.8 | 14.7 | 18.6 |
(a) Define the term relative atomic mass of an element.
(b) Use the data above to calculate the relative atomic mass.
(c) Suggest the identity of M .
(d) Describe how ionisation is achieved in a mass spectrometer.
(e) Give three reasons why ionisation is necessary.
See the answers to the right.
Answers.
(a) average mass of an atom / all the isotopes
relative to the mass of a C-12 atom
(b) Ar = (64 × 0.389) + (66 × 0.278) + (67 × 0..147) + (68 × 0.186) = 65.7
(c) Zinc
(d) electron gun (fires) electrons or high speed/energy electrons
( not just bombarded by electrons or bombarded by electron gun )
knocks off an electron from M
(may be earned from a real or generic equation)
(e) – to allow ions to be accelerated (by an electric field)
– deflected (by a magnet/magnetic field)
– detected / description of current formed at the detector/sensor