CPC Chemical Analysis & Techniques 3 — Questions and Answers
Question 1: Which property of X-ray fluorescence (XRF) makes it useful for elemental analysis?
- It measures molecular vibrations
- Each element emits characteristic secondary X-rays when excited (Correct answer)
- It separates elements by mass
- It measures electron spin transitions
Correct answer: Each element emits characteristic secondary X-rays when excited
When primary X-rays excite atoms, each element emits characteristic fluorescent X-rays at wavelengths unique to that element, enabling identification and quantification.
Question 2: In HPLC, what is the difference between isocratic and gradient elution?
- Isocratic uses multiple columns; gradient uses one
- Isocratic maintains constant mobile phase composition; gradient changes it over time (Correct answer)
- Isocratic is for gases; gradient is for liquids
- Isocratic uses UV detection; gradient uses fluorescence
Correct answer: Isocratic maintains constant mobile phase composition; gradient changes it over time
Isocratic elution uses a constant mobile phase composition throughout the run, while gradient elution systematically changes solvent strength to improve separation of complex mixtures.
Question 3: What analytical technique uses the principle of inductively coupled plasma to excite atoms for emission detection?
- ICP-OES (Correct answer)
- FTIR
- GC-MS
- NMR
Correct answer: ICP-OES
ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) uses an argon plasma at ~6000-10000 K to excite atoms, which then emit characteristic light at element-specific wavelengths.
Question 4: In titration analysis, what is the equivalence point?
- The point where the indicator changes color
- The point where moles of titrant exactly equal moles of analyte (Correct answer)
- The midpoint of the titration curve
- The point of maximum buffer capacity
Correct answer: The point where moles of titrant exactly equal moles of analyte
The equivalence point is where the amount of titrant added is stoichiometrically equal to the analyte, representing complete reaction.
Question 5: Which spectroscopic technique provides information about the functional groups in an organic molecule through molecular vibrations?
- UV-Vis spectroscopy
- Infrared (IR) spectroscopy (Correct answer)
- Atomic emission spectroscopy
- X-ray diffraction
Correct answer: Infrared (IR) spectroscopy
IR spectroscopy identifies functional groups based on characteristic absorption frequencies of molecular bond stretching and bending vibrations.
Question 6: What is the Van Deemter equation used to describe in chromatography?
- Relationship between detector response and concentration
- Factors contributing to band broadening and plate height as a function of flow rate (Correct answer)
- The retention time as a function of stationary phase polarity
- The resolution between two peaks
Correct answer: Factors contributing to band broadening and plate height as a function of flow rate
The Van Deemter equation describes how plate height (H) varies with mobile phase velocity, accounting for eddy diffusion (A), longitudinal diffusion (B), and mass transfer (C) terms.
Question 7: In coulometry, what is the fundamental principle used for quantitative analysis?
- Beer-Lambert law relating absorbance to concentration
- Faraday's law relating charge passed to moles of analyte (Correct answer)
- Nernst equation relating potential to ion activity
- Henry's law relating pressure to dissolved gas
Correct answer: Faraday's law relating charge passed to moles of analyte
Coulometry uses Faraday's law, where the total electrical charge (coulombs) passed is directly proportional to the moles of analyte oxidized or reduced.
CPC Chemical Analysis & Techniques 3
Which property of X-ray fluorescence (XRF) makes it useful for elemental analysis?