Free Analytical Chemistry MCQs with Answers

31. The term accuracy refers to how near the observed value is to

• A. Mean value
• B. Low value
• C. True value
• D. None of above

Explanation: Accuracy is a measure of how close an experimental measurement is to the true or accepted value of the quantity being measured. It is a measure of the correctness of the result.

32. The nuclei you think is invisible in NMR spectroscopy is:

• A. N14
• B. P31
• C. Cl35
• D. C13

Explanation: NMR spectroscopy requires nuclei with non-zero spin to be detected. Cl³⁵ has a quadrupolar nucleus with spin 3/2 and often gives broad, weak, or undetectable signals, making it practically "invisible" in routine NMR. Nuclei like C¹³, H¹, N¹⁴, and P³¹ are commonly detectable.

33. In the detection of nitrogen in an organic compound The appearance of Prussian blue colouration is due to the formation of:

• A. Fe4[Fe(CN6)]3
• B. Na3[Fe(CN)6]
• C. K3[Fe(CN)6]
• D. None

Explanation: In the Lassaigne's test, nitrogen in an organic compound forms sodium cyanide (NaCN) when fused with Na. On adding Fe²⁺ ions, it reacts with CN⁻ to form ferric ferrocyanide (Fe₄[Fe(CN)₆]₃). This compound is Prussian blue, giving the characteristic blue coloration.

34. The auxochrome not concern with Metanil yellow dye:

• A. -SO3H
• B. -OH
• C. -NH2
• D. Both -SO3H and -NH2

Explanation: Auxochromes are groups that enhance color by altering the electron distribution in a chromophore. Metanil yellow dye contains -SO₃H (solubility) and -NH₂ (color intensification) as auxochromes. The -OH group is not present and thus does not contribute to this dye's color.

35. What device is used for the identification of isotopes of elements having solid-state?

• A. Aston spectrometer
• B. Dempster's mass spectrometer
• C. Soddy mass spectrometer
• D. Atomic spectrometer

Explanation: The Aston mass spectrometer was designed to separate and identify isotopes based on their mass-to-charge ratio. It is particularly useful for solid elements that can be vaporized in the instrument. Thus, Aston's spectrometer is the standard device for solid-state isotope identification.

36. Anything under test or observation in laboratory is called:

• A. Surrounding
• B. System
• C. Confined space
• D. None of these

Explanation: In laboratory terminology, a system is the part of the universe under study or observation. Everything outside the system is called the surroundings. Thus, option B correctly defines the substance or process being tested.

37. A Buffer Solution is used to:

• A. Change the pH drastically
• B. Resist changes in pH
• C. Act as a strong acid
• D. Act as a strong base
• E. Add color to the solution

Explanation: A buffer contains a weak acid and its conjugate base (or vice versa). It neutralizes added acids or bases, maintaining nearly constant pH. Thus, its main role is to resist pH changes

38. In gravimetric analysis, a substance is usually weighed in the form of:

• A. Its original compound
• B. A volatile compound
• C. An insoluble precipitate
• D. A dissolved solution

Explanation: Gravimetric analysis involves precipitating the analyte in a stable, pure form. The precipitate is filtered, dried, and weighed to determine the amount of substance. Using an insoluble precipitate ensures accurate and precise measurement.

39. The arithmetic mean of the different deviations observed in several measurements of the same quantity is known as

• A. The standard deviation
• B. The average deviation
• C. Relative mean deviation
• D. Variance

Explanation: This is the definition of average deviation. It is calculated by finding the absolute difference of each measurement from the mean, summing these differences, and then dividing by the number of measurements.

40. The coefficient of variance (C.V.) is defined as

• A. C.V.= (8 X 100) / X
• B. C.V.=(x X 100) / 8
• C. C.V.= (x X 8) / 100
• D. C.V.= (8 X 1000) / X

Explanation: The coefficient of variation is a standardized measure of the dispersion of a data set. It is defined as the ratio of the standard deviation (s) to the mean (x̄), often expressed as a percentage: (s / x̄) × 100.