Free Analytical Chemistry MCQs with Answers

91. Select the incorrect Statement:

• A. Molecule may gain an electron to form a molecular anion.
• B. Molecule may lose an electron to form a molecular cation.
• C. Molecular cations are less abundant than molecular anions.
• D. These molecular ions can be formed by passing a high-energy electron beam through a gas.

Explanation: Abundance of cationic molecular ions is due to the ability to stabilize unpaired electrons which makes the formation of cationic molecular ions energetically less demanding. That's why cationic molecular ions are more abundant than anionic ones.

92. Choose the correct Statement:

• A. The most direct and accurate method for determining atomic masses uses mass spectrometry.
• B. An indirect but precise method for determining molecular masses is through mass spectrometry.
• C. Collision between electrons and atoms produces negative ions by the absorption of electrons by atoms or molecules.
• D. The first significant application of mass spectrometry was demonstrating the detection of isotopes of Argon.

Explanation: Electron Collision. Often, electron collisions with gas molecules result in electron attachment to the molecule, which forms a negative ion.

93. Molar extinction coefficient (ε) a constant in Beer- Lambert law is the characteristics of the:

• A. Solute
• B. Solvent
• C. Concentration
• D. All of the above

Explanation: Under defined conditions of solvent, pH, and temperature the molar absorption coefficient for a particular compound is a constant at the specified wavelength. Furthermore, it is used to calculate concentration using A = εLcWhere A is the amount of light absorbed by the sample for a particular wavelength,ε is the molar extinction coefficient, L is the distance that the light travels through the solution, and c is the concentration of the absorbing species per unit volume. Hence, it is a characteristic of concentration, as well as solute, and solvent.

94. What is true about modern methods used in the determination of the structure of compounds?

• A. Accurate but more time consuming
• B. Accurate, rapid but chemicals are used in large amounts
• C. Accurate, rapid but sophisticated and complicated
• D. Accurate, simple and less time consuming

Explanation: The modern methods used by scientists to identify and differentiate between cell structures are efficient, accurate, simple, and less time-consuming in comparison to the methods used in the past. Examples are IR spectroscopy, mass spectroscopy, NMR, etc.

95. Which region of electromagnetic spectrum is involved in nuclear magnetic resonance microwave(NMR spectroscopy)?

• A. Microwave
• B. Radio wave
• C. Infrared region
• D. X-rays

Explanation: NMR spectroscopy works by applying a radio frequency to the sample, specific to the nuclei of interest. The energy from the radio frequency pulse is enough to flip the nuclei from its Alpha position to the Beta.

96. The electronic transition that is involved in the visible region is:

• A. σ - σ
• B. d - d
• C. π - π
• D. π - σ

Explanation: d-d transitions are electronic transitions that occur between the molecular orbitals that are mostly metallic in character; specifically between the d-orbitals of a transition metal complex. When electronic transitions occur between these orbitals, the color observed is complementary to the wavelengths absorbed in the visible region.

97. 100% transmission in IR spectroscopy means:

• A. No absorption
• B. 50% absorption
• C. 75% absorption
• D. 100% absorption

Explanation: When IR radiation is passed through a sample, some of it is absorbed and some of it paasses through (transmitted). A 100% transmission means the sample does not absorb any IR radiation.

98. Chemical shift in NMR spectroscopy is expressed as delta (δ) or tan (t) scale. Choose the correct relationship between δ and t:

• A. δ = 10 - t
• B. δ = 10 + t
• C. t = δ - 10
• D. t = 10 - δ

Explanation: In NMR spectroscopy, δ (delta) represents the chemical shift, while t is another scale used to express the same concept. The correct relationship between these two scales is δ = 10 - t. This means that to convert from the t scale to the δ scale, you subtract the tan value from 10. The other options are incorrect because they either add instead of subtract, reverse the roles of δ and t, or suggest a subtraction that doesn't reflect the true relationship.

99. 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.

100. 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.