ACS CP Chemical Principles & Laboratory Techniques 3 — Questions and Answers
Question 1: When performing a Karl Fischer titration, what species is being directly quantified?
- Total acidity
- Water content (Correct answer)
- Dissolved oxygen
- Chloride ion
Correct answer: Water content
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?
- O–H stretch of carboxylic acid
- C=O stretch of a ketone (Correct answer)
- N–H bend of a primary amine
- C–H stretch of alkane
Correct answer: C=O stretch of a ketone
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?
- Below 400 K
- Above 400 K (Correct answer)
- Below 200 K
- Above 200 K
Correct answer: Above 400 K
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?
- Erlenmeyer flask
- Graduated cylinder
- Volumetric flask (Correct answer)
- Beaker
Correct answer: Volumetric flask
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?
- The ion with the highest mass-to-charge ratio
- The most abundant ion in the spectrum (Correct answer)
- The molecular ion
- The ion formed by loss of a methyl group
Correct answer: The most abundant ion in the spectrum
The base peak is the most abundant ion in the mass spectrum and is assigned a relative intensity of 100%.
Question 6: Which of the following is the BEST description of the Nernst equation in electrochemistry?
- It relates cell potential to temperature only
- It relates equilibrium constant to standard free energy
- It corrects standard cell potential for non-standard concentrations (Correct answer)
- It defines the relationship between current and resistance
Correct answer: It corrects standard cell potential for non-standard concentrations
The Nernst equation (E = E° – RT/nF · ln Q) adjusts standard electrode potential for actual solution concentrations and activities.
Question 7: What is the purpose of an internal standard in analytical chemistry?
- To calibrate the instrument response and correct for sample preparation variability (Correct answer)
- To set the blank reading to zero
- To increase the pH of the sample
- To prevent matrix interferences by precipitation
Correct answer: To calibrate the instrument response and correct for sample preparation variability
An internal standard is added in a known quantity to correct for variations in injection volume, extraction efficiency, and instrument response.
ACS CP Chemical Principles & Laboratory Techniques 3
When performing a Karl Fischer titration, what species is being directly quantified?