Summary
Mass spectrometry and infrared spectroscopy are analytical techniques used to identify unknown substances by analyzing molecular ions and absorption of infrared energy, respectively.
- Mass Spectrometry — a technique that uses high energy electrons to create and analyze positively charged molecular ions. Example: Identifying isotopes by their mass-to-charge (m/e) ratio.
- Isotopes — atoms of the same element with different numbers of neutrons. Example: Cl-35 and Cl-37 are isotopes of chlorine.
- Infrared Spectroscopy — a method that measures the absorption of IR radiation by molecules, causing vibrations. Example: Identifying functional groups by their characteristic absorption peaks in an IR spectrum.
- m/e Ratio — the ratio of the mass of a particle to its charge, used in mass spectrometry. Example: An ion with mass 16 and charge 2+ has an m/e value of 8.
- Base Peak — the peak corresponding to the most abundant ion in a mass spectrum. Example: The tallest peak in a mass spectrum.
Exam Tips
Key Definitions to Remember
- Mass Spectrometry
- Isotopes
- Infrared Spectroscopy
- m/e Ratio
- Base Peak
Common Confusions
- Confusing isotopes with ions
- Misinterpreting the m/e ratio as mass alone
Typical Exam Questions
- What is the purpose of mass spectrometry? To identify unknown substances by analyzing molecular ions.
- How do isotopes differ from each other? They have different numbers of neutrons but the same number of protons.
- What does an IR spectrum tell us about a molecule? It identifies functional groups based on absorption peaks.
What Examiners Usually Test
- Understanding of how mass spectrometry identifies isotopes
- Ability to interpret IR spectra to identify functional groups
- Knowledge of the significance of the m/e ratio in mass spectrometry
