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Year 11 - Science

Mass spectrometry

Chemical analysis

Unit Summary

This unit covers tests to identify aqueous cations and anions, including flame tests for metal ions like lithium, sodium, and copper. It explains the benefits of instrumental analysis, such as sensitivity and accuracy, and focuses on interpreting results from charts, tables, and spectroscopy data.

Lesson Summary

You will learn to explain how mass spectrometry is used to identify isotopes and molecular structures, and calculate relative atomic masses.

Key Notes

  • Isotopes are atoms of the same element with different numbers of neutrons.
  • Relative abundances of isotopes can be used to calculate the relative atomic mass (RAM) of an element.
  • Mass spectrometry ionises samples to create positive ions for analysis.
  • The M⁺ peak represents the molecular ion, indicating the molecular mass.
  • Fragmentation in mass spectrometry helps identify molecular structure by breaking molecules into smaller ions.

Vocabulary To Learn

  • isotope: An atom of an element with the same number of protons, but different number of neutrons.
  • relative atomic mass: An average value that takes account of the abundance of the isotopes of the element.
  • molecular mass: The sum of the atomic masses of all the atoms in a molecule.
  • molecular ion: The ion produced when the molecule is ionised by loss of an electron from the molecule.
  • spectrometer: An apparatus used for recording and measuring spectra, especially as a method of analysis.

Common Mistakes To Avoid

  • All peaks in a mass spectrum represent intact (and neutral) molecules or atoms.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key points.

Isotopes are atoms of the same element with different numbers of neutrons. Relative abundances of isotopes can be used to calculate the relative atomic mass (RAM) of an element.

2. Define this scientific word and use it in context. 'isotope'

An atom of an element with the same number of protons, but different number of neutrons. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: All peaks in a mass spectrum represent intact (and neutral) molecules or atoms. Correction: Clarify that in mass spectrometry, all detected peaks represent ionised species, not neutral molecules or atoms. The peaks can correspond to either the molecular ion (M⁺) or smaller ionised fragments, as well as different isotopes of an element.

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