Chemical Analysis & Techniques Flashcards
7 cards from real CPC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Chemical Analysis & Techniques flashcards as text
A chemist observes a systematic error in all replicate measurements. Which type of error does this represent?
Answer: Systematic (determinate) error
Systematic errors consistently shift measurements in one direction due to a constant flaw in the method, instrument, or analyst technique, affecting accuracy but not precision.
In gas chromatography, what determines the order in which analytes elute from the column?
Answer: Their relative affinity for the stationary phase versus the mobile phase
Analytes elute in order of their partition coefficients between the stationary and mobile phases; compounds with stronger affinity for the stationary phase elute later.
Which method is most appropriate for determining the identity of an unknown crystalline solid?
Answer: X-ray powder diffraction (XRPD)
X-ray powder diffraction produces a unique diffraction pattern (fingerprint) for each crystalline substance, enabling definitive identification of unknown solid phases.
What is the purpose of a blank in analytical measurements?
Answer: To measure background signal and correct for matrix and reagent contributions
A blank contains all reagents and solvents except the analyte, allowing correction for background absorbance or signal contributed by the matrix and reagents.
In nuclear magnetic resonance (NMR) spectroscopy, what does chemical shift measure?
Answer: The electronic environment of nuclei relative to a reference compound
Chemical shift (in ppm) reflects differences in the resonance frequency of nuclei due to varying electron density in their local chemical environment.
Which sample digestion method uses high pressure and microwave energy to rapidly dissolve solid matrices?
Answer: Microwave-assisted acid digestion
Microwave-assisted acid digestion uses sealed vessels and microwave energy to rapidly dissolve samples under elevated temperature and pressure, minimizing contamination and analyte loss.
What is the role of the nebulizer in ICP-OES analysis?
Answer: To convert liquid sample into a fine aerosol for introduction into the plasma
The nebulizer converts the liquid sample into a fine aerosol of droplets, which are then carried by argon gas into the plasma torch for atomization and excitation.