10 Questions
What happens when the heat of the flame excites an electron in an atom?
The electron moves to a higher energy level.
What type of energy is released when an excited atom relaxes back to the ground state?
Light energy
In which region of an IR spectrum are peaks difficult to assign individual peaks?
Below 1500 cm^-1
What is the name given to any analytical technique that uses the electromagnetic spectrum to probe a material?
Spectroscopy
What type of light is shone at a sample in Infrared (IR) spectroscopy?
Infrared light
What technique is often combined with spectroscopy as a useful analytical method?
Mass spectrometry
What can be used to determine whether two samples are identical based on their IR spectra?
"Fingerprint" region
Which technique uses light energy absorption based on vibrating bonds in molecules?
Infrared spectroscopy
What is the main purpose of using IR spectroscopy for analyzing the unknown white powder?
To identify functional groups in the powder
What do peaks in the fingerprint region of an IR spectrum correspond to?
Functional groups in the molecule
Study Notes
Melting Point Analysis
- Impurities can change the melting point of a substance
- Impurities usually lower the melting point
- Melting point analysis is used to determine the purity of a substance
Determining the Structure of Molecules
- Four steps to determine the structure of a molecule:
- Test and purify the materials
- Identify the molecular formula
- Identify functional groups
- Determine the structure
Elemental Analysis
- Elemental analysis is used to identify the molecular formula
- Autosampler and furnace are used to separate the elements
- H2O, NO2, and CO2 traps are used to measure the percentage of hydrogen, nitrogen, and carbon respectively
- Empirical formula is the simplest ratio of atoms of each element present in a compound
- Molecular formula is the actual number of atoms of each element in one molecule
Calculating Molecular Formulae
- Molecular formula = empirical formula × a whole number
- The whole number is the ratio of the relative molecular mass (Mr) to the empirical formula relative mass (Er)
Mass Spectrometry
- Mass spectrometry is an analytical technique that can determine:
- The relative molecular mass of a molecule
- Some information about the structure of the molecule
- Isotope masses and isotopic abundance of an element
- The process of mass spectrometry involves:
- Ionization of the sample
- Acceleration of ions and fragments
- Detection of the molecular ion peak and fragmentation patterns
- Fragmentation patterns can provide clues about the structure of the molecule
- The presence of an ion peak does not always prove the presence of a fragment
Fragmentation Patterns
- Fragmentation patterns can be used to identify the structure of a molecule
- The presence of certain fragments can indicate the length of a carbon chain
- The more stable the ion, the more likely it is to reach the detector and the higher the peak
Infrared (IR) Spectroscopy
- IR spectroscopy is used to identify functional groups in a molecule
- IR light is shone at a sample, and some wavelengths are absorbed depending on the bonds present
- The fingerprint region of an IR spectrum is below 1500 cm-1 and is used for direct comparisons
- Peaks in the IR spectrum correspond to functional groups
Spectroscopy
- Spectroscopy is the name given to any analytical technique that uses the electromagnetic spectrum to probe a material
- Types of spectroscopy include:
- X-ray spectroscopy
- UV-vis spectroscopy
- Infrared spectroscopy
- Rotational spectroscopy
- NMR spectroscopy
- Mass spectrometry
This quiz covers topics related to molecular ion peaks, isotopes, and fragmentation in mass spectrometry. Understand how molecular ions break apart upon ionization to form fragment ions at lower m/z values.
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