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

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:

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.

Concept:

Quantum Dots

• Quantum dots are nanoscale semiconductor particles that exhibit quantum mechanical properties.
• They typically range in size from 2 to 10 nanometers and are small enough to confine electrons in all three spatial dimensions.
• This quantum confinement effect gives them unique optical and electronic properties, such as size-tunable emission of light when excited.

Explanation:

• Semiconducting nanoparticles that emit light when excited: Quantum dots are semiconducting nanoparticles that absorb energy and emit light at specific wavelengths depending on their size, making them ideal for applications like bioimaging and quantum computing.
• Metallic nanoparticles with unique optical properties: Metallic nanoparticles exhibit surface plasmon resonance, which differs from the quantum confinement effects seen in quantum dots.
• Magnetic nanoparticles used for data storage: Magnetic nanoparticles are primarily used in data storage or biomedical applications and do not exhibit light emission properties like quantum dots.
• Carbon-based nanoparticles with high electrical conductivity: Carbon-based nanoparticles, such as graphene or carbon nanotubes, are known for their conductivity but are not quantum dots.

Therefore, the correct answer is: Semiconducting nanoparticles that emit light when excited.

Concept:

Size and Shape-Dependent Optical Properties of Nanoparticles

• The optical properties of nanoparticles, such as their color, are influenced by their size, shape, and the surrounding environment.
• This phenomenon arises from the interaction of light with the surface electrons of nanoparticles, leading to localized surface plasmon resonance (LSPR) in metallic nanoparticles.
• Changes in nanoparticle size and shape alter the wavelength of light absorbed and scattered, resulting in a visible color change.

Explanation:

• Tyndall effect: This refers to the scattering of light by particles in a colloid, but it does not explain the color change based on nanoparticle size and shape.
• Rayleigh scattering: This describes the scattering of light by particles much smaller than the wavelength of light, not specifically related to nanoparticle-induced color changes.
• Mie scattering: This phenomenon describes the scattering of light by particles of comparable size to the wavelength of light, which is responsible for the color changes in nanoparticle solutions. It accounts for the interaction between light and surface plasmons in nanoparticles.
• Colorimetric effect: While this term relates to color changes, it is not the specific term used for the optical behavior of nanoparticles due to size and shape variations.

Therefore, the correct answer is: Mie scattering.

Concept:

X-ray Diffraction (XRD)

• X-ray diffraction is a powerful analytical technique used to study the crystalline nature of materials.
• It works by analyzing the pattern produced when X-rays are scattered by the regular arrangement of atoms in a crystalline material.
• The technique is governed by Bragg's Law:

  nλ = 2d sinθ

  where λ is the wavelength of the X-ray, d is the interplanar spacing, and θ is the angle of incidence.

Explanation:

• Size: While XRD can provide information about crystallite size through line broadening analysis (using the Scherrer equation), this is not its primary purpose.
• Shape: The shape of nanomaterials is typically studied using microscopic techniques like TEM or SEM, not XRD.
• Crystal structure: The primary application of XRD is to determine the crystal structure, including lattice parameters, symmetry, and atomic arrangement of materials.
• Surface area: Surface area is analyzed using techniques like BET (Brunauer-Emmett-Teller) analysis, not XRD.

Therefore, the correct answer is: Crystal structure.

Concept:

Stoichiometry and Theoretical Yield

• The theoretical yield is the maximum amount of product that can be formed from the given reactants, based on the stoichiometry of the reaction.
• For the reaction:

  \(N_2 + 3H_2 \to 2NH_3\)

  the stoichiometric ratio is:

  1 mole of N₂ reacts with 3 moles of H₂ to produce 2 moles of NH₃.

• To determine the theoretical yield, the limiting reactant must first be identified:

  Limiting reactant = reactant that will be completely consumed first, limiting the formation of the product.

Explanation:

Given:

• Moles of N₂ = 2
• Moles of H₂ = 8

From the stoichiometric ratio:

1 mole of N₂ reacts with 3 moles of H₂.

For 2 moles of N₂, the required moles of H₂ are:

Required H₂ = 2 × 3 = 6 moles

Available H₂ = 8 moles, which is greater than the required amount. Hence, N₂ is the limiting reactant.

From the stoichiometric ratio:

1 mole of N₂ produces 2 moles of NH₃.

For 2 moles of N₂, the theoretical yield of NH₃ is:

Theoretical yield = 2 × 2 = 4 moles

Therefore, the theoretical yield of NH₃ is 4 moles.

Concept:

Hardness in Water

• Water hardness refers to the concentration of multivalent metal ions in water, which can form insoluble precipitates with soap and scale in boilers and pipes.
• The most common ions responsible for hardness are calcium (Ca²⁺) and magnesium (Mg²⁺).
• Hardness can be categorized as:
  • Temporary hardness: Caused by bicarbonates of calcium and magnesium, removable by boiling.
  • Permanent hardness: Caused by chlorides and sulfates of calcium and magnesium, removable only through chemical treatment.

Explanation:

• Calcium and magnesium ions: These are the primary contributors to both temporary and permanent hardness in water. They form insoluble compounds with soap and scale deposits in pipes and equipment.
• Sodium and potassium ions: These ions do not cause hardness as they form soluble compounds and do not react with soap to form scum.
• Chloride and sulfate ions: Although these ions are part of some compounds causing hardness (e.g., calcium sulfate), they themselves do not directly cause hardness.
• Iron and manganese ions: These ions can contribute to water quality issues such as staining and taste, but they are not the primary cause of hardness.

Therefore, the correct answer is calcium and magnesium ions.