modern analytical techniques I Flashcards
“How can you determine the relative atomic mass of an element using a mass spectrum?”
“By analyzing the relative isotopic abundances shown in the spectrum.”
“What process occurs in a mass spectrometer to produce a mass spectrum?
The molecules in the sample are bombarded with electrons, forming molecular ions (M+).”
“What peak in a mass spectrum represents the molecular ion?”
“The peak with the highest m/z value, known as the M peak.”
“How do you find the relative molecular mass of a compound using a mass spectrum?
“By looking at the mass/charge value of the molecular ion peak (M peak).”
“What does the y-axis represent in a mass spectrum?”
“The abundance of ions, often expressed as a percentag
“How are the units on the x-axis typically denoted in a mass spectrum?”
“As ‘mass/charge’ ratio.”
“What effect do bombarding electrons have on some molecular ions in a mass spectrometer?”
“They cause some molecular ions to break up into fragments.”
“What is a fragmentation pattern in a mass spectrum?”
“It is the pattern formed by the fragments of molecular ions, which helps in identifying molecules and their structure.”
“What components are visible on a mass spectrum?”
“Only the ions are visible, while the free radicals are ‘lost’.”
“What process is involved in determining the structural formula from a mass spectrum?”
“Identifying the ions responsible for each peak based on their m/z values.”
“What assumption is made when determining the ions responsible for peaks in a mass spectrum?”
“That the m/z value of a peak matches the mass of the ion that produced it.”
“Why can you differentiate between two different compounds containing the same atoms using mass spectrometry?”
“Because they won’t produce exactly the same set of fragments in the mass spectrum.”
“How does each compound contribute to the uniqueness of its mass spectrum?”
“By producing a different set of peaks, making the spectrum act as a fingerprint for the compound.”
“How are large computer databases of mass spectra utilized in identifying compounds?”
“They can be used to match the spectrum of an unknown compound with those in the database, aiding in compound identification.”
“What happens when a beam of infrared (IR) radiation is passed through a sample of a chemical in IR spectroscopy?”
“The IR radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy.”
“How do bonds between different atoms behave in terms of absorbing IR radiation?”
“Bonds between different atoms absorb different frequencies of IR radiation.”
“Why do bonds in different locations within a molecule absorb different frequencies of IR radiation?”,
“Because bonds in different places in a molecule have different vibrational frequencies.
“What does an infrared spectrometer graph show?”
“It shows the frequencies of radiation absorbed by the molecules, aiding in identifying the functional groups in a molecule.”
“How are peaks represented on an IR spectrum?”
“The peaks are represented as pointing downwards.”
“What is plotted on the y-axis and x-axis of an IR spectrum graph?”
“Transmittance is plotted on the y-axis, and wavenumber (frequency) is plotted on the x-axis.”
“How is infrared spectroscopy useful in determining changes in functional groups during a reaction?”
“It can detect changes such as the disappearance of certain absorption peaks, like the O-H absorption when oxidizing an alcohol to an aldehyde, and the appearance of new absorption peaks, like the C=O absorption.”
“What changes would you observe in the IR spectrum when oxidizing an alcohol to an aldehyde?”
“The O-H absorption peak would disappear, and a C=O absorption peak would appear.”
“What additional changes occur in the IR spectrum when further oxidizing an aldehyde to a carboxylic acid?”
“An O-H peak at a slightly lower frequency than before would appear alongside the C=O peak.”
