Analytical Chemistry 1 — Questions and Answers
Question 1: What is the principle of UV-Vis spectroscopy?
- Measurement of fluorescence
- Measurement of absorption (Correct answer)
- Measurement of conductivity
- Measurement of ionization energy
Correct answer: Measurement of absorption
UV-Vis spectroscopy is an analytical technique that measures the absorption of ultraviolet and visible light by a sample. When light passes through a substance, specific wavelengths are absorbed by electrons transitioning to higher energy levels. The amount of light absorbed at different wavelengths provides information about the concentration and electronic structure of the absorbing species.
Question 2: Which technique separates compounds based on their boiling points?
- Mass spectrometry
- NMR spectroscopy
- Gas chromatography (Correct answer)
- IR spectroscopy
Correct answer: Gas chromatography
Gas chromatography (GC) is a powerful analytical technique used to separate and analyze compounds that can be vaporized without decomposition. It separates components of a mixture based on their differential partitioning between a stationary phase and a mobile gas phase, with separation primarily driven by differences in their boiling points and interactions with the stationary phase. Components with lower boiling points typically elute faster.
Question 3: What is the purpose of a reference electrode in potentiometry?
- To control temperature
- To provide a stable potential (Correct answer)
- To measure current
- To ionize the sample
Correct answer: To provide a stable potential
In potentiometry, a reference electrode is crucial because it provides a stable and known potential against which the potential of the indicator electrode is measured. This constant potential allows for accurate determination of the potential difference, which is then related to the concentration of the analyte in the solution. Without a stable reference, precise measurements would not be possible.
Question 4: Which of the following is a primary standard in titration?
- Hydrochloric acid
- Sodium carbonate (Correct answer)
- Sodium hydroxide
- Ammonium hydroxide
Correct answer: Sodium carbonate
A primary standard is a highly pure, stable, non-hygroscopic substance of precisely known composition that can be accurately weighed to prepare a solution of exact concentration. These solutions are then used to standardize other solutions in titration. Sodium carbonate (Na2CO3) meets these criteria and is commonly used as a primary standard for standardizing strong acids.
Question 5: What is the principle of gravimetric analysis?
- Measurement of light absorption
- Measurement of mass (Correct answer)
- Measurement of volume
- Measurement of conductivity
Correct answer: Measurement of mass
Gravimetric analysis is a quantitative analytical method that determines the amount of an analyte by precisely measuring its mass. The analyte is selectively converted into an insoluble precipitate, which is then isolated, purified, dried, and weighed. The mass of the precipitate is used to calculate the original amount or concentration of the analyte in the sample.
Question 6: Which chromatography technique uses a liquid mobile phase?
- Gas chromatography
- Thin-layer chromatography
- Liquid chromatography (Correct answer)
- Ion-exchange chromatography
Correct answer: Liquid chromatography
Chromatography techniques are classified based on the nature of their mobile and stationary phases. Liquid chromatography (LC) specifically utilizes a liquid as its mobile phase to carry the sample through a stationary phase, which can be a solid or a liquid supported on a solid. This broad category includes techniques like High-Performance Liquid Chromatography (HPLC), used for separating a wide range of compounds.
Analytical Chemistry 1
What is the principle of UV-Vis spectroscopy?