ACS CP Chemical Principles & Laboratory Techniques 3

Question 1

When performing a Karl Fischer titration, what species is being directly quantified?

Accepted Answer

Water content

Answer

Karl Fischer titration is a specific volumetric method for determining water content based on the reaction of iodine with water.

Question 2

Which bond in an organic molecule absorbs infrared radiation near 1710 cm⁻¹?

Accepted Answer

C=O stretch of a ketone

Answer

The C=O stretch of ketones appears near 1715 cm⁻¹, which is a strong, characteristic absorption in the IR spectrum.

Question 3

A reaction has ΔH° = –80 kJ/mol and ΔS° = –200 J/(mol·K). At what temperature does the reaction become non-spontaneous?

Accepted Answer

Above 400 K

Answer

Setting ΔG° = 0: T = ΔH°/ΔS° = (–80,000 J/mol)/(–200 J/mol·K) = 400 K; above 400 K, ΔG° becomes positive.

Question 4

Which glassware is most appropriate for preparing a precise volume of standard solution in quantitative analysis?

Accepted Answer

Volumetric flask

Answer

Volumetric flasks are calibrated to contain a precise volume at a specific temperature, making them ideal for preparing standard solutions.

Question 5

In mass spectrometry, what is the base peak?

Accepted Answer

The most abundant ion in the spectrum

Answer

The base peak is the most abundant ion in the mass spectrum and is assigned a relative intensity of 100%.

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