Free Spectroscopy and Analysis MCQs with Answers

41. The water formed in the combustion analysis is usually absorbed by:

• A. Mg (NO3)2
• B. Mg (ClO4)2
• C. Mg (OH)2
• D. Mg (ClO2)2

Explanation: The correct answer is Mg (ClO4)2, or magnesium perchlorate, which is widely used in combustion analysis as a drying agent due to its hygroscopic properties. It effectively absorbs moisture from its surroundings, making it ideal for removing water formed during combustion processes. Other compounds listed, such as magnesium nitrate, magnesium hydroxide, and magnesium chlorite, do not possess the same level of hygroscopic ability and are not typically used for this purpose.

42. The spin states of a nucleus of an atom in absence of applied magnetic field have:

• A. Different energies
• B. Equal energies
• C. Zero energies
• D. High energies

Explanation: In the absence of an applied magnetic field, the spin states of a nucleus of an atom have equal energies. Each spin state corresponds to a possible orientation of the nuclear spin angular momentum, but without the influence of an external magnetic field, these states remain at the same energy level. When an external magnetic field is applied, the energy levels split, a phenomenon known as nuclear Zeeman splitting. This splitting occurs because the magnetic field interacts with the magnetic moment associated with the nuclear spin, resulting in different energy levels.The incorrect options fail to acknowledge that, without an external magnetic field, the energy levels remain equal. Option A suggests different energies, which only occurs when a magnetic field is present. Option C claims zero energies, overlooking the inherent energies due to nuclear spin. Option D suggests high energies, which is inaccurate as the energy levels without a magnetic field are typically low.

43. The functional group region in infra-red spectrum lies between:

• A. 500 - 1300 cm-1
• B. 600 - 1500 cm-1
• C. 1500 - 4000 cm-1
• D. 2500 - 3500 cm-1

Explanation: The functional group region in an infrared spectrum ranges from 1500 to 4000 cm-1. This is where the characteristic absorption peaks of various functional groups, such as -OH, -NH, and C=O, are typically observed. Option A (500 - 1300 cm-1) and Option B (600 - 1500 cm-1) fall within the fingerprint region, which is known for the unique absorption patterns of entire molecules rather than specific functional groups. Option D (2500 - 3500 cm-1) is a subset of the functional group region, but it doesn't cover the entire range where functional groups can be detected, making Option C the most accurate choice.

44. The infrared spectra commonly referred to as IR spectra is usually expressed as:

• A. Wavelength
• B. Wavenumber
• C. Frequency
• D. All of the above

Explanation: The correct answer is All of the above. Infrared spectra can be expressed in terms of wavelength, wavenumber, or frequency, each offering distinct advantages in different contexts:Wavelength: Useful for comparing spectra from different sources or under varying conditions.Wavenumber: Ideal for calculations related to molecular vibrations, providing a unit independent of sample physical properties.Frequency: Relevant for speed-related calculations of IR radiation.While each unit is valid, the context and specific requirements of the analysis determine the most appropriate choice. Hence, IR spectra are commonly expressed using any of these units.

45. Which of the following radiations cannot cause excitation in the molecule ?

• A. Red Colour
• B. Green Colour
• C. Ultra Voilet
• D. None of the above

Explanation: The answer is D as all the mentioned radiations can excite molecules.All electromagnetic radiation, including red and green colours of visible light, have the potential to cause excitation in molecules, although the likelihood of excitation increases with higher-energy radiation such as ultraviolet (UV) and X-rays. Therefore, all the options given in the question can cause excitation in molecules to some extent, and hence the correct answer is D) None of the above.

46. How many types of "NMR" protons are there in Isopropyl chloride?

• A. 2
• B. 6
• C. 4
• D. 8

Explanation: In isopropyl chloride, there are 6 different types of "NMR" protons. This means that there are 6 unique environments for the protons in the molecule, leading to distinct signals in the nuclear magnetic resonance (NMR) spectrum. Each type of proton corresponds to a specific chemical environment within the molecule.

47. Which of the following methods, relatively gives more information about the structure of an organic compound:

• A. Mass Spectroscopy
• B. NMR Spectroscopy
• C. IR Spectroscopy
• D. U.V Visible Spectroscopy

Explanation: Among the options provided, NMR (Nuclear Magnetic Resonance) Spectroscopy gives more detailed information about the structure of an organic compound. It provides insights into the connectivity of atoms, the arrangement of functional groups, and the environment around specific nuclei (like hydrogen and carbon). This technique is especially powerful in elucidating the stereochemistry of molecules. Therefore, option b is correct.