Questions Set-5 Instrumentation Questions

INSTRUMENTATION

Q1. What is the purpose of a monochromator in a spectrophotometer?

a. To focus the light onto the sample

b. To separate light into its component wavelengths

c. To detect the intensity of the transmitted light

d. To stabilize the light source

ANSWER:

b. To separate light into its component wavelengths

EXPLANATION:

A monochromator disperses light into its component wavelengths using a prism or grating, allowing the selection of a specific wavelength for analysis.

Q2. Which is the criteria for electronic spin resonance?

a. Periodic change in polarizability

b. Spin quantum number of nuclei > 0

c. Presence of unpaired electron in a molecule

d. Presence of chromophore in a molecule

ANSWER:

c. Presence of unpaired electron in a molecule

EXPLANATION:

Electronic Spin Resonance (ESR), also known as Electron Paramagnetic Resonance (EPR), is a technique used to study molecules with unpaired electrons.

The key criterion for ESR is the presence of unpaired electrons in a molecule. These unpaired electrons interact with an external magnetic field, leading to energy transitions that can be detected using ESR.

Q3. Given below are two statements

Statement I: Emission spectrum results when an electron in an atom undergoes a transition from excited state to ground state.

Statement II: transition takes place with the emission of a photon of energy hv.

In the light of the above statements, choose the most appropriate answer from the options given below

a. both statement I and II are correct

b. both statement I and II are incorrect

c. Statement I is correct but statement II is incorrect

d. Statement I is incorrect but statement II is correct

ANSWER:

a. Both statement I and II are correct

EXPLANATION:

When an electron in an atom is excited (i.e., it has absorbed energy and moved to a higher energy level), it can return to its ground state (or lower energy level) by releasing the excess energy. This release of energy results in the emission of light, which forms the emission spectrum of the atom.

When the electron transitions from a higher energy level to a lower one, it emits a photon whose energy EEE is equal to the difference between the two energy levels. This energy is related to the frequency v of the emitted photon by the equation E=hv, where h is Planck's constant and v is the frequency of the emitted light.

Q4. What are the main criteria on which mass spectrometer used for?

a. Composition in sample

b. Relative mass of atoms

c. Concentration of elements in the sample

d. Properties of sample

ANSWER:

b. Relative mass of atoms

EXPLANATION:

Mass spectrometry is primarily used to determine the relative mass of atoms or molecules in a sample. The mass spectrometer measures the mass-to-charge ratio (m/z) of ions, providing information about the molecular weight of the analytes and their isotopic distribution.

Q5. ESI and MALDI belong to which of the following techniques?

a. Detection

b. Analysis

c. Acceleration

d. Ionization

ANSWER:

d. Ionization

EXPLANATION:

ESI (Electrospray Ionization) and MALDI (Matrix-Assisted Laser Desorption/Ionization) are both ionization techniques used in mass spectrometry to convert neutral molecules into charged particles (ions).

Q6. Which of the following technique is used to determine the protein sequence?

a. X-ray crystallography

b. NMR spectroscopy

c. Atomic Spectroscopy

d. Mass Spectroscopy

ANSWER:

d. Mass Spectroscopy

EXPLANATION:

Mass spectrometry (MS) is a powerful technique used to determine the protein sequence by identifying the mass-to-charge ratio (m/z) of peptides generated by enzymatic digestion (e.g., using trypsin) of the protein. The peptide fragments are analyzed to deduce the sequence of amino acids in the protein, and techniques like Tandem Mass Spectrometry (MS/MS) are commonly used for this purpose. MS provides both qualitative and quantitative information about the protein's structure, including sequence, modifications, and molecular weight.

Q7. Given below are two statements

Statement I: Molecular spectra arises from transition of an electron between the molecular energy levels.

Statement II: In molecular transitions, electronic, rotational and vibration transitions occurs.

In the light of the above statements, choose the most appropriate answer from the options given below

a. both statement I and II are correct

b. both statement I and II are incorrect

c. Statement I is correct but statement II is incorrect

d. Statement I is incorrect but statement II is correct

ANSWER:

a. Both statement I and II are correct

EXPLANATION:

Molecular spectra result from transitions between different energy levels of molecules. These energy levels can include electronic, vibrational, and rotational levels, and the absorption or emission of light occurs when electrons in the molecule move between these energy levels.

Molecular transitions can involve:

• Electronic transitions: Where electrons in a molecule move between different electronic energy levels.

• Vibrational transitions: Where molecules absorb or emit energy corresponding to changes in their vibrational states.

• Rotational transitions: Where molecules absorb or emit energy associated with rotations around their center of mass.

Q8. Given below are two statements

Statement I: IR spectroscopy helps in the determination of force constant from vibrational spectrum.

Statement II: It helps in determination of purity.

In the light of the above statements, choose the most appropriate answer from the options given below

a. both statement I and II are correct

b. both statement I and II are incorrect

c. Statement I is correct but statement II is incorrect

d. Statement I is incorrect but statement II is correct

ANSWER:

a. Both statement I and II are correct

EXPLANATION:

In infrared (IR) spectroscopy, the absorption of IR radiation by molecules occurs when their natural vibrational frequencies match the frequency of the IR light. The force constant (which is related to the strength of the bond between atoms) can be determined by analyzing the vibrational frequencies in the IR spectrum. The stretching or bending vibrations of bonds provide information about the force constant, which can be calculated from the frequency of the observed vibrations.

Q9. Given below are two statements

Statement I: Infrared spectra can identify the unknown materials.

Statement II: it can determine the amount of components in a mixture and quality of a sample.

In the light of the above statements, choose the most appropriate answer from the options given below

a. both statement I and II are correct

b. both statement I and II are incorrect

c. Statement I is correct but statement II is incorrect

d. Statement I is incorrect but statement II is correct

ANSWER:

a. Both statement I and II are correct

EXPLANATION:

Infrared (IR) spectroscopy is widely used to identify unknown materials by comparing their IR spectra to known reference spectra. The unique pattern of absorption frequencies in the IR spectrum is characteristic of specific functional groups and molecular structures. By analyzing these absorption peaks, one can determine the chemical composition of an unknown substance.

IR spectroscopy can be used to determine the amount of a specific component in a mixture by measuring the intensity of characteristic absorption peaks.

Q10. Which of the following shift leads to the decreased intensity of absorption?

a. Hypochromic

b. Hyperchromic

c. Hypsochromic

d. Bathochromic

ANSWER:

a. Hypochromic

EXPLANATION:

Hypochromic shift refers to a decrease in the intensity of absorption. This shift occurs when the absorption of light by a molecule becomes weaker, typically due to changes in molecular interactions, solvent effects, or other structural changes.

Hyperchromic shift refers to an increase in the intensity of absorption, meaning the absorption becomes stronger.

Hypsochromic shift refers to a shift to shorter wavelengths (blue shift), which is associated with a change in the energy of the absorption band, but not specifically related to intensity.

Bathochromic shift refers to a shift to longer wavelengths (red shift), which again is related to the position of the absorption band, but not to the intensity.

Author:- Bhawana Sharma