Analytical Chemistry MCQ Quiz in বাংলা - Objective Question with Answer for Analytical Chemistry - বিনামূল্যে ডাউনলোড করুন [PDF]

Concept:

Column resolution is a measure of how well a chromatography column can separate two closely eluting peaks. It is defined as the difference in retention time (t_R) of two adjacent peaks divided by the sum of their peak widths at the base (w). Mathematically, the column resolution (R_s) can be expressed as:

Rs =  Δz = t_r2-t_r1

The higher the column resolution, the better the separation of two peaks. A resolution value of 1.5 or higher is considered good for most chromatographic separations. The column resolution can be improved by increasing the column length, reducing the particle size of the stationary phase, using a more selective mobile phase, or adjusting other chromatographic conditions.

Explanation:

Column resolution, R_s = 

where, wA and wB are the widths at the base for A and B respectively and ΔZ is the difference in time of their arrival at the electron.

∴ ΔZ = 17.63 − 16.40 = 1.23

wA + wB = 1.11 + 1.21 = 2.32

R_s = 

= 1.06

Conclusion: The correct answer is option 1.

CONCEPT:

Atomic Force Microscopy (AFM)

• Atomic Force Microscopy (AFM) is a type of scanning probe microscopy with high resolution.
• It works by scanning a sharp tip over the surface of a sample to measure the forces between the tip and the surface.
• The resolution of AFM is determined by the interaction between the scanning tip and the sample surface.

EXPLANATION:

• In AFM characterization:

  The applied force between the tip and the surface is crucial for obtaining high-resolution images.

  • If the force is too high, it can damage the sample or the tip.
  • If the force is too low, it may not provide enough interaction to obtain accurate topographical details.
• Other factors such as the speed of the scanning tip, the temperature of the sample, and the wavelength of the incident light do not directly impact the resolution of the AFM images.

Therefore, the correct answer is The applied force between the tip and the surface.

CONCEPT:

Green Chemistry and Nanotechnology

• Green chemistry involves designing chemical processes and products to reduce or eliminate the use and generation of hazardous substances.
• Nanotechnology involves manipulating materials on an atomic or molecular scale.
• The overlap of green chemistry and nanotechnology is focused on developing environmentally friendly methods for producing nanomaterials.

EXPLANATION:

• One of the green methods used to prevent environmental harm while producing nanoparticles is utilizing microwave-assisted synthesis in a solvent-free environment.
• This method is considered green because:
  • Microwave-assisted synthesis provides energy-efficient heating, which reduces energy consumption.
  • A solvent-free environment minimizes the use of hazardous organic solvents, which can be harmful to the environment.
  • This method typically results in shorter reaction times and higher yields of nanoparticles.

Therefore, the correct green method specifically used to prevent environmental harm while producing nanoparticles is utilizing microwave-assisted synthesis in a solvent-free environment (Option 1).

CONCEPT:

Effect of Nanoscale Size on Magnetic Properties

• At the nanoscale, the properties of materials can significantly differ from their bulk counterparts due to quantum effects and increased surface area to volume ratio.
• Magnetic properties of materials at the nanoscale can be altered due to changes in domain structure and thermal fluctuations.
• Superparamagnetism is a form of magnetism which appears in small ferromagnetic or ferrimagnetic nanoparticles. In this state, the magnetization can randomly flip direction under the influence of temperature.

EXPLANATION:

• When ferromagnetic materials are reduced to the nanoscale, the size of the particles can become comparable to the size of magnetic domains.
• At this scale, thermal energy can overcome the magnetic anisotropy energy, leading to the phenomenon known as superparamagnetism.
• In the superparamagnetic state, the magnetization of the nanoparticles can rapidly fluctuate, and they do not retain magnetization in the absence of an external magnetic field.
• Therefore, the reduction in size to the nanoscale can cause ferromagnetic materials to become superparamagnetic.

Therefore, the correct answer is option 3: The reduction in size to the nanoscale can cause ferromagnetic materials to become superparamagnetic.

CONCEPT:

X-Ray Diffraction (XRD)

• X-ray diffraction (XRD) is a powerful analytical technique used to determine the crystallographic structure of materials.
• XRD can provide detailed information about the atomic arrangement in a material, including the interplanar spacing (d-spacing) and crystallite size.
• The technique is based on the constructive interference of monochromatic X-rays and a crystalline sample.
• The X-rays interact with the crystal lattice and are diffracted at specific angles, which can be measured to determine the lattice parameters and crystallite size.

EXPLANATION:

• In nanomaterials characterization, XRD is particularly useful for studying the atomic scale structure of nanoparticles.
  • XRD provides information on the interplanar spacing (d-spacing) by analyzing the diffraction pattern produced when X-rays are scattered by the crystal lattice.
  • The crystallite size can be estimated using the Scherrer equation, which relates the width of the diffraction peaks to the size of the crystallites.
• Other techniques like Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), and Scanning Electron Microscopy (SEM) provide different types of information and are not as specific for determining interplanar spacing and crystallite size.
  • AFM provides topographical information at the nanoscale level.
  • TEM offers high-resolution imaging and can provide structural information but not typically used for precise crystallite size determination.
  • SEM gives surface morphology and composition information but does not provide detailed crystallographic data.

Therefore, the correct answer is X-Ray Diffraction (XRD).

CONCEPT:  

Nanomaterials in Catalysis

• Nanomaterials are materials with structural components smaller than 100 nanometers (nm) in at least one dimension.
• Due to their small size, nanomaterials exhibit unique physical and chemical properties that are significantly different from their bulk counterparts.
• One of the most important properties of nanomaterials, especially for catalysis, is their high surface-to-volume ratio.

EXPLANATION:

• The high surface-to-volume ratio of nanomaterials means that a larger fraction of the atoms or molecules are present on the surface compared to bulk materials.
  • This provides more active sites for catalytic reactions, enhancing the efficiency and effectiveness of the catalyst.
• Increased electronic conductivity, enhanced mechanical strength, and low solubility in solvents can be beneficial properties for specific applications, but they are not the primary reasons why nanomaterials are excellent candidates for catalysis.
  • While increased electronic conductivity can improve the transport of electrons in some catalytic processes, it does not directly contribute to the number of active sites available.
  • Enhanced mechanical strength can improve the durability of the catalyst, but it does not affect the catalytic activity itself.
  • Low solubility in solvents can be important for the stability of the catalyst in certain reactions, but again, it does not directly increase the number of active sites.

Therefore, the primary reason why nanomaterials are considered excellent candidates for applications in catalysis is due to their high surface-to-volume ratio that provides more active sites.

CONCEPT:

Surface Plasmon Resonance (SPR) of Gold Nanoparticles

• Surface plasmon resonance (SPR) is a phenomenon that occurs when conduction electrons on the surface of a nanoparticle oscillate in resonance with the incident light wave.
• The SPR effect is highly sensitive to the physical parameters of the nanoparticles, particularly their size and shape.
• The optical properties of gold nanoparticles are primarily determined by their size and shape, which influence the frequency and intensity of the SPR.

EXPLANATION:

• In the context of gold nanoparticles:

  The SPR of gold nanoparticles is highly dependent on their physical dimensions.

  • Smaller nanoparticles exhibit SPR at shorter wavelengths (blue shift), while larger nanoparticles exhibit SPR at longer wavelengths (red shift).
  • The shape of the nanoparticles also plays a critical role: for example, spherical nanoparticles have different SPR characteristics compared to rod-shaped or triangular nanoparticles.
• Other factors like the concentration of the nanoparticle solution, surface charge density, and the temperature of the synthesis reaction can affect the overall behavior of the nanoparticles but do not primarily determine the SPR.

Therefore, the factor that plays a critical role in determining the optical properties of gold nanoparticles in terms of SPR is their size and shape.

CONCEPT:

Thermogravimetric Analysis (TGA) for CaCO₃/CaO Mixture

• CaCO₃ decomposes on heating as follows:

  CaCO₃(s) → CaO(s) + CO₂(g)

• Only CaCO₃ loses mass (as CO₂ escapes), CaO remains unchanged.
• Thus, total mass loss is only due to decomposition of CaCO₃.

EXPLANATION:​

• Mass loss = 155.2 - 125.3 = 29.9 mg
• This mass corresponds to the loss of CO₂.
• Molecular weight of CaCO₃ = 100 g/mol, CO₂ = 44 g/mol
• So, from 100 g CaCO₃, 44 g CO₂ is lost
• Using proportion:
  • 44 g CO₂ → 100 g CaCO₃
  • 29.9 mg CO₂ → x mg CaCO₃
  • x = (100 × 29.9) / 44 = **67.95 mg of CaCO₃**
• Total original sample = 155.2 mg
• Percentage of CaCO₃ = (67.95 / 155.2) × 100 ≈ 43.8%

Therefore, the percentage of CaCO₃ in the mixture is 43.8% .

Concept:

Techniques for Measuring Nanoparticle Size Distribution

• Several techniques are used to measure the size and size distribution of nanoparticles, depending on the medium and the desired resolution.
• Dynamic Light Scattering (DLS): This is a widely used technique for measuring the size distribution of nanoparticles in solution.
• DLS works by analyzing the scattering of light from nanoparticles undergoing Brownian motion in a liquid medium.

Explanation:

• TEM (Transmission Electron Microscopy): TEM provides high-resolution images of individual nanoparticles, allowing precise size measurement but not an overall size distribution in solution.
• SEM (Scanning Electron Microscopy): SEM is used to image nanoparticles on a solid substrate and cannot measure size distribution in a solution.
• DLS (Dynamic Light Scattering): DLS is specifically suited for measuring the size distribution of nanoparticles in liquid solutions, making it the best technique for this purpose.
• XRD (X-ray Diffraction): XRD provides information on crystallite size, not the size distribution of nanoparticles in solution.

Therefore, the correct answer is: DLS.

Concept:

Surface Charge of Nanoparticles

• The surface charge of nanoparticles is an essential parameter that affects their stability, interaction, and behavior in various environments.
• This charge is commonly quantified using the zeta potential, which represents the electrokinetic potential at the slipping plane of particles in a dispersion.

Explanation:

• DLS (Dynamic Light Scattering): This technique measures the size and size distribution of nanoparticles but does not directly measure surface charge.
• Zeta potential measurement: This is the primary technique used to determine the surface charge of nanoparticles by analyzing their electrophoretic mobility in a fluid under an electric field.
• UV-Vis spectroscopy: This technique is used to study the optical properties of nanoparticles but is not suitable for measuring surface charge.
• XPS (X-ray Photoelectron Spectroscopy): XPS provides information about the elemental composition and chemical state of the nanoparticle surface but not its charge.

Therefore, the correct answer is: Zeta potential measurement.