ACS CP Chemical Principles & Laboratory Techniques 5

Question 1

Which spectroscopic technique provides information about the oxidation state and coordination environment of a metal in a sample?

Accepted Answer

X-ray photoelectron spectroscopy (XPS)

Answer

XPS measures binding energies of core electrons, which are sensitive to the oxidation state and chemical environment of an element.

Question 2

The Henderson-Hasselbalch equation assumes which condition that may not hold in concentrated solutions?

Accepted Answer

Activity coefficients equal to 1 (ideal behavior)

Answer

The Henderson-Hasselbalch equation uses concentrations in place of activities, which is only valid when activity coefficients ≈ 1 (dilute solutions).

Question 3

Which of the following best describes a Type II error in hypothesis testing within analytical chemistry?

Accepted Answer

Failing to detect a real difference between two populations

Answer

A Type II (false negative) error occurs when the null hypothesis is not rejected even though it is actually false.

Question 4

What is the primary purpose of a Soxhlet extractor in laboratory practice?

Accepted Answer

Continuously extract a solid sample with a recycling solvent

Answer

A Soxhlet extractor allows continuous extraction of soluble components from a solid matrix using a solvent that is repeatedly recycled.

Question 5

In cyclic voltammetry, what does the ratio of anodic to cathodic peak currents (ipa/ipc ≈ 1) indicate?

Accepted Answer

A reversible (electrochemically reversible) redox couple

Answer

A peak current ratio near 1 and a peak potential separation near 59/n mV indicate a diffusion-controlled, electrochemically reversible redox couple.

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