Free Analytical Chemistry MCQs with Answers

61. Mass spectrum of Magnesium shows that it contains three isotopes. Mg-24 (78.70%), Mg-25 (10.13%) & Mg-26(11.17%). The average atomic mass of Mg is

• A. 24.32 amu
• B. 25.32 amu
• C. 26.32 amu
• D. 27.32 amu

Explanation: To calculate the average atomic mass, we use the formula:Average atomic mass=(Abundance1×Atomic mass1)+(Abundance2×Atomic mass2)+(Abundance3×Atomic mass3)Substituting the values:Average atomic mass=(0.7899×23.98504 )+(0.1000×24.98584 )+(0.1101×25.98259 )Average atomic mass=18.99254 +2.49858 +2.86561 Average atomic mass=24.35673 So, the average atomic mass of magnesium is approximately 24.35673

62. Which of the following electronic transitions requires highest amount of energy when a compound is interacted with ultraviolet radiations?

• A. n → Π
• B. Π → Π
• C. 8 → 8
• D. n → 8

Explanation: This transition involves the excitation of an electron from a non-bonding orbital (n) to another orbital (8). If 8 represents a higher energy orbital, this transition could require a significant amount of energy, potentially more than the other transitions listed, depending on the specific molecular orbitals involved.

63. Height of peak in mass spectrum shows:

• A. Number of isotopes
• B. Mass number
• C. Relative abundace of isotopes
• D. Number of protons

Explanation: Option c is the correct answer. The height of a peak in a mass spectrum is directly proportional to the relative abundance of ions with that particular mass-to-charge ratio. Higher peaks indicate higher abundance of ions with that mass-to-charge ratio.

64. Which region of electromagnetic spectrum is involved in bonds vibrations?

• A. Ultraviolet
• B. Infrared
• C. Radio waves
• D. Microwaves

Explanation: Infrared radiation is involved in bond vibrations. When molecules vibrate, their bonds stretch, bend, and twist. These vibrational motions correspond to specific frequencies of infrared radiation. Infrared spectroscopy is a technique used to study these vibrations, providing valuable information about molecular structure and composition.

65. The characteristic signal of carbonyl carbon if acetone in I.R spectrum will be detected at:

• A. 3200cm-1
• B. 1200cm-1
• C. 800cm-1
• D. 1720cm-1

Explanation: This is the correct answer. The characteristic signal of the carbonyl carbon in acetone (CH3COCH3) is typically found in the region around 1720 cm-1. This corresponds to the stretching vibration of the C=O bond in the carbonyl group.

66. During isotopic analysis, the pressure of the vapours of the ions maintained in the ionization chamber of mass spectrometer Is:

• A. Around 10-7 torr
• B. 1 torr
• C. Around 10-3 torr
• D. 10-7 torr

Explanation: Explanation:The pressure of these vapors is kept very low that 10-6 to 10-7 torr. "1 torr" is a higher pressure range that may be used in some mass spectrometers for certain types of analyses, but it is generally not used for isotopic analysis. These options are also incorrect. During isotopic analysis, the pressure of the vapors of the ions maintained in the ionization chamber of mass spectrometer is around 10-7 torr, not 10-3 or any other.

67. Which of the following shows maximum penetration?

• A. Electrons
• B. Protons
• C. Alpha particles
• D. Neutrons

Explanation: α-particles consist of 2 protons and 2 neutrons, which have 4 times higher mass than neutrons, and thus low penetration power. Beta particles are much smaller and more penetrating than alpha particles, but their range in tissue is still limited.Due to their large mass and being chargeless in nature, neutrons have high kinetic energy and thus, high penetration power.

68. X-rays were discovered by:

• A. W. Roentgen
• B. De Broglie
• C. Young
• D. Michelson

Explanation: The correct answer is A. Wilhelm Conrad Roentgen discovered X-rays on November 8, 1895, while experimenting with cathode-ray tubes. He observed a new form of invisible radiation that could penetrate various materials, naming it 'X-rays.' Roentgen's discovery had a significant impact on medical imaging and various scientific and industrial applications.Option B, De Broglie, is incorrect as he was known for his work on wave-particle duality in quantum theory, not for discovering X-rays. Option C, Young, is incorrect as Thomas Young was famous for his double-slit experiment demonstrating the wave nature of light, not X-rays. Option D, Michelson, is incorrect as Albert A. Michelson's contributions were in measuring the speed of light precisely and developing interferometers, not in the discovery of X-rays.

69. At which of the following m/e values would you not expect to find a peak in the mass spectrum of ethanoyl chloride?

• A. 35.5
• B. 37
• C. 4.3
• D. 78

Explanation: c) 4.3:The m/e value of 4.3 is an unusual and specific value. It is not commonly associated with any ions or fragments that would be expected in the mass spectrum of ethanoyl chloride. Therefore, you would not expect to find a peak at 4.3 in the mass spectrum of ethanoyl chloride.

70. The low resolution proton spectrum of a compound contains two peaks. Which of the following compounds could not give this spectrum?

• A. Propane
• B. Butane
• C. 2-methylpropane
• D. 2,2 - dimethylpropane

Explanation: b) Butane:Butane is a four-carbon alkane with the molecular formula C4H10. In the low-resolution proton spectrum of butane, you would also expect to see two peaks. One peak would represent the three equivalent protons (CH3 group) and the other peak would represent the six equivalent protons (CH2 group) in the molecule. Therefore, butane could give a spectrum with two peaks.