A mass spectrum of a gaseous sample of an element shows two prominent peaks. The first peak occurs at m/z = 35 with a relative intensity of 100 arbitrary units, while the second peak occurs at m/z = 37 with a relative intensity of 32 arbitrary units. No other peaks rise above the instrument’s detection threshold.
Assume all ions are singly charged and that the peaks correspond to different isotopes of the same element.
(a) Identify the two isotopes present and rank them in order of relative abundance.
(b) Estimate the percent abundance of each isotope, showing how the values are obtained from the stated peak intensities.
(c) Using the values you obtained in part (b), calculate the average atomic mass of the element and compare it with the tabulated periodic-table value. Explain, in words, how the isotopic abundances give rise to the listed average atomic mass.
(d) Describe qualitatively what change, if any, you would expect in the mass spectrum if the same element were isolated from a sample that was artificially enriched in the lighter isotope. Justify your prediction.