ACS CP ACS CP Spectroscopy & Chemical Analysis

Question 1

In nuclear magnetic resonance (NMR) spectroscopy, chemical shift (δ) is reported in ppm relative to which standard reference compound for 1H NMR?

Accepted Answer

Tetramethylsilane (TMS) at δ 0.00 ppm

Answer

Tetramethylsilane (TMS) is the universal reference standard for NMR spectroscopy, assigned a chemical shift of 0.00 ppm because its 12 equivalent protons resonate at a unique, upfield position.

Question 2

Beer-Lambert Law (A = εlc) states that absorbance is directly proportional to concentration only when:

Accepted Answer

The solution is dilute and the radiation is monochromatic

Answer

Beer-Lambert Law holds for dilute solutions (no solute-solute interactions) and monochromatic light; concentrated solutions, stray light, or polychromatic radiation cause deviations from linearity.

Question 3

In mass spectrometry, the base peak is defined as:

Accepted Answer

The most abundant (tallest) ion peak in the mass spectrum, assigned 100% relative abundance

Answer

The base peak is the most abundant ion in the mass spectrum, assigned 100% relative intensity; all other peaks are reported as a percentage of the base peak intensity.

Question 4

Fourier transform infrared spectroscopy (FTIR) measures molecular vibrations. Which bond vibration type appears at approximately 1715 cm⁻¹ in the IR spectrum?

Accepted Answer

C=O stretch of ketones/aldehydes

Answer

The carbonyl C=O stretching vibration of ketones and aldehydes appears as a strong, sharp absorption around 1715 cm⁻¹ (ketones) to 1725 cm⁻¹ (aldehydes) in the IR spectrum.

Question 5

High-performance liquid chromatography (HPLC) in reverse-phase mode uses which type of stationary and mobile phase?

Accepted Answer

Nonpolar stationary phase (C18) with polar mobile phase (water/acetonitrile)

Answer

Reverse-phase HPLC uses a nonpolar C18 (octadecylsilane) bonded silica stationary phase with a polar aqueous/organic mobile phase, retaining nonpolar compounds longer.

(ACS CP) American Chemical Society (ACS) Certified Professional Practice Test

(ACS CP) American Chemical Society (ACS) Certified Professional Practice Test

ACS CP ACS CP Spectroscopy & Chemical Analysis