Chemistry Test Analytical Chemistry 3

Question 1

In HPLC, what distinguishes reverse-phase from normal-phase chromatography?

Accepted Answer

Reverse-phase uses a nonpolar stationary phase (e.g., C18) and a polar mobile phase

Answer

Reverse-phase HPLC uses a nonpolar stationary phase (like C18 silica) and a polar aqueous/organic mobile phase, opposite to normal-phase.

Question 2

What is the purpose of an internal standard in quantitative analytical chemistry?

Accepted Answer

To compensate for variations in sample preparation and instrument response

Answer

An internal standard is added in a known amount to correct for losses or variability during sample preparation and analysis.

Question 3

Which method of standard addition is most useful when the sample matrix interferes with the analytical signal?

Accepted Answer

Standard addition method

Answer

The standard addition method adds known quantities of analyte to the sample, accounting for matrix effects that external calibration cannot address.

Question 4

In potentiometry, the Nernst equation relates electrode potential to which variable?

Accepted Answer

Ion activity (concentration)

Answer

The Nernst equation (E = E° − (RT/nF)ln Q) shows that electrode potential depends on the activity (effectively concentration) of the ion.

Question 5

What is the limit of detection (LOD) in analytical chemistry?

Accepted Answer

The smallest amount of analyte that can be reliably distinguished from a blank

Answer

LOD is the minimum analyte quantity that produces a signal distinguishable from background noise, typically defined as blank signal plus 3 standard deviations.

Chemistry Practice Test

Chemistry Practice Test

Chemistry Test Analytical Chemistry 3