Safety and evidence boundary
Use supplied spectra and datasets only. No physical apparatus is required.
Explicit science instruction
A simplified mass spectrum can be read as a set of signals at different mass-to-charge values with intensities related to relative abundance.
For a singly charged ion in a simple classroom model, horizontal position can correspond approximately to isotope mass while peak height or area reflects relative abundance.
The instrument output is evidence, not the isotope itself. Calibration, charge state, and detector response are part of the interpretation boundary.
Vocabulary: mass spectrum; mass-to-charge ratio; relative abundance; peak intensity; calibration.
Worked example with reasoning
Synthetic spectrum: m/z 24 has intensity 79, m/z 25 has 10, and m/z 26 has 11. If normalized to 100 total units, the approximate abundances are 79%, 10%, and 11%.
Guided question
A spectrum has peaks at 63 and 65 with relative intensities 69 and 31. State the approximate abundances and identify which isotope contributes more strongly to the weighted average.
Independent work
- Normalize a three-peak synthetic spectrum to percentages.
- Sketch the spectrum with correct relative heights.
- List two assumptions required before treating peak intensity as direct isotope abundance.
Misconception check
The tallest peak is not automatically the heaviest isotope. Height represents relative signal; horizontal position represents mass-to-charge information.
Formative understanding check
What different information is represented by peak position and peak intensity?
Reveal worked response
Peak position represents mass-to-charge information; intensity represents relative signal and, under the simplified model, relative abundance.
Public self-check only.
Mentor evidence conference
Ask Archaemenes to challenge one assumption behind your conversion from peak intensity to isotope abundance.
Teacher guidance
Foundation: Read peak positions and rank abundances.
Core: Normalize a multi-peak spectrum and explain the evidence.
Extended: Discuss how an unrecognized charge state could change mass-to-charge interpretation.