A sealed ampoule labeled “Halogen X” is analyzed in a high-resolution mass spectrometer. Because the instrument counts individual ions, the raw data are reported as ion counts rather than percentages. The instrument detects two peaks for singly charged ions:
• m/z=34.9689 with 75,780 counts
• m/z=36.9659 with 24,220 counts
A chemist consults the following average atomic masses (in amu) for candidate halogens:
• Argon: 39.948
• Chlorine: 35.45
• Bromine: 79.904
(a) Convert the ion counts to percent relative abundance for each isotope.
(b) Use your results from part (a) to calculate the average atomic mass of Halogen X.
(c) Identify Halogen X from the candidates listed, and justify the elimination of the other possibilities using specific numerical evidence.
(d) Bromine also exhibits a two-isotope pattern. Explain why Bromine can be ruled out even before numerical calculations by comparing qualitative features of its natural isotopic composition with the spectrum provided.