A student analyzes an unknown metal using mass spectrometry
CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
A student analyzes an unknown metal using mass spectrometry. Two peaks are observed for singly charged ions at m/z=63.0 and m/z=65.0. The detector records 69.1% of the total ion current at m/z=63.0 and 30.9% at m/z=65.0.
Reference data (average atomic masses, in amu):
• Copper: 63.546
• Zinc: 65.38
• Gallium: 69.723
The laboratory report states that the mass spectrometer has an instrumental uncertainty of ±0.02amu on each measured m/z value.
(a) Calculate the weighted average atomic mass of the unknown metal from the spectrum.
(b) Identify the metal by comparing your calculated value with the reference data. Clearly explain how the stated instrumental uncertainty influences the confidence of your identification.
(c) If the same spectrum had been recorded with peak positions each shifted higher by 0.03amu relative to the true values, discuss whether your conclusion in part (b) would change and justify your reasoning quantitatively.