MS MS in Chemistry 2

Question 1

In gas chromatography (GC), the stationary phase separates compounds primarily based on:

Accepted Answer

Polarity and volatility interactions with the column

Answer

GC separation depends on differential partitioning of analytes between the mobile gas phase and the stationary liquid or solid phase, governed by volatility and polarity interactions.

Question 2

The Henderson-Hasselbalch equation, pH = pKa + log([A−]/[HA]), is most useful for:

Accepted Answer

Calculating buffer pH when the ratio of conjugate base to weak acid is known

Answer

The Henderson-Hasselbalch equation directly calculates buffer pH from the pKa and the ratio of deprotonated to protonated species, provided neither form is negligible.

Question 3

Which electrochemical technique measures the current as a function of applied potential while analyte concentration is varied to generate calibration data?

Accepted Answer

Voltammetry

Answer

Voltammetry (e.g., cyclic or differential pulse voltammetry) sweeps the applied potential and records resulting current, allowing quantitative determination of analyte concentrations.

Question 4

In HPLC with a reverse-phase column, which solvent system would elute a polar compound first?

Accepted Answer

90% water / 10% acetonitrile

Answer

In reverse-phase HPLC, polar compounds have less affinity for the nonpolar C18 stationary phase and elute earlier in high-aqueous (polar) mobile phases.

Question 5

Beer-Lambert Law (A = εbc) relates absorbance to concentration. If you double the path length (b) while halving the concentration (c), absorbance will:

Accepted Answer

Remain the same

Answer

Since A = ε·b·c and both b and c change by reciprocal factors (×2 and ×0.5), their product b·c is unchanged, so absorbance remains constant.

MS - Master of Science Practice Test

MS - Master of Science Practice Test

MS MS in Chemistry 2