CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
During a quality-control check, a mass spectrometer was found to introduce a systematic calibration offset of +0.25amu to every measured m/z value. Before the flaw was discovered, a technician recorded the following spectrum for a purified sample containing singly charged ions:
Recorded m/z (amu)
Recorded relative abundance (%)
22.25
90.9
23.25
9.1
A periodic-table excerpt lists the following average atomic masses (amu):
• Neon: 20.180
• Sodium: 22.990
• Magnesium: 24.305
• Fluorine: 18.998
Assume no other isotopes for the element exceed 0.1% abundance.
(a) Correct the recorded m/z values to obtain the true isotope masses.
(b) Determine the average atomic mass of the element from the corrected data.
(c) Identify the element by comparing your calculated value to the periodic-table excerpt. Justify the rejection of each alternative element using quantitative arguments that include the stated systematic error.
(d) Explain qualitatively how the miscalibrated instrument could have led to an incorrect elemental identification had the error not been discovered.