modern analytical techniques I

Question 1

“How can you determine the relative atomic mass of an element using a mass spectrum?”

Answer 1

“By analyzing the relative isotopic abundances shown in the spectrum.”

Question 2

“What process occurs in a mass spectrometer to produce a mass spectrum?

Answer 2

The molecules in the sample are bombarded with electrons, forming molecular ions (M+).”

Question 3

“What peak in a mass spectrum represents the molecular ion?”

Answer 3

“The peak with the highest m/z value, known as the M peak.”

Question 4

“How do you find the relative molecular mass of a compound using a mass spectrum?

Answer 4

“By looking at the mass/charge value of the molecular ion peak (M peak).”

Question 5

“What does the y-axis represent in a mass spectrum?”

Answer 5

“The abundance of ions, often expressed as a percentag

Question 6

“How are the units on the x-axis typically denoted in a mass spectrum?”

Answer 6

“As ‘mass/charge’ ratio.”

Question 7

“What effect do bombarding electrons have on some molecular ions in a mass spectrometer?”

Answer 7

“They cause some molecular ions to break up into fragments.”

Question 8

“What is a fragmentation pattern in a mass spectrum?”

Answer 8

“It is the pattern formed by the fragments of molecular ions, which helps in identifying molecules and their structure.”

Question 9

“What components are visible on a mass spectrum?”

Answer 9

“Only the ions are visible, while the free radicals are ‘lost’.”

Question 10

“What process is involved in determining the structural formula from a mass spectrum?”

Answer 10

“Identifying the ions responsible for each peak based on their m/z values.”

Question 11

“What assumption is made when determining the ions responsible for peaks in a mass spectrum?”

Answer 11

“That the m/z value of a peak matches the mass of the ion that produced it.”

Question 12

“Why can you differentiate between two different compounds containing the same atoms using mass spectrometry?”

Answer 12

“Because they won’t produce exactly the same set of fragments in the mass spectrum.”

Question 13

“How does each compound contribute to the uniqueness of its mass spectrum?”

Answer 13

“By producing a different set of peaks, making the spectrum act as a fingerprint for the compound.”

Question 14

“How are large computer databases of mass spectra utilized in identifying compounds?”

Answer 14

“They can be used to match the spectrum of an unknown compound with those in the database, aiding in compound identification.”

Question 15

“What happens when a beam of infrared (IR) radiation is passed through a sample of a chemical in IR spectroscopy?”

Answer 15

“The IR radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy.”

Question 16

“How do bonds between different atoms behave in terms of absorbing IR radiation?”

Answer 16

“Bonds between different atoms absorb different frequencies of IR radiation.”

Question 17

“Why do bonds in different locations within a molecule absorb different frequencies of IR radiation?”,

Answer 17

“Because bonds in different places in a molecule have different vibrational frequencies.

Question 18

“What does an infrared spectrometer graph show?”

Answer 18

“It shows the frequencies of radiation absorbed by the molecules, aiding in identifying the functional groups in a molecule.”

Question 19

“How are peaks represented on an IR spectrum?”

Answer 19

“The peaks are represented as pointing downwards.”

Question 20

“What is plotted on the y-axis and x-axis of an IR spectrum graph?”

Answer 20

“Transmittance is plotted on the y-axis, and wavenumber (frequency) is plotted on the x-axis.”

Question 21

“How is infrared spectroscopy useful in determining changes in functional groups during a reaction?”

Answer 21

“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.”

Question 22

“What changes would you observe in the IR spectrum when oxidizing an alcohol to an aldehyde?”

Answer 22

“The O-H absorption peak would disappear, and a C=O absorption peak would appear.”

Question 23

“What additional changes occur in the IR spectrum when further oxidizing an aldehyde to a carboxylic acid?”

Answer 23

“An O-H peak at a slightly lower frequency than before would appear alongside the C=O peak.”