STP Laboratory Practice 3 — Questions and Answers
Question 1: What is the primary purpose of a fume hood in a chemistry laboratory?
- To keep the laboratory temperature stable
- To protect the worker from inhaling hazardous vapors, gases, and aerosols (Correct answer)
- To prevent contamination of samples from the environment
- To store volatile chemicals safely
Correct answer: To protect the worker from inhaling hazardous vapors, gases, and aerosols
A fume hood protects laboratory personnel by drawing hazardous airborne contaminants away from the breathing zone.
Question 2: According to Good Laboratory Practice (GLP), when must a laboratory notebook entry be corrected?
- By erasing the error completely so it cannot be read
- By using correction fluid (white-out) to cover the error
- By drawing a single line through the error, initialing, dating, and writing the correction (Correct answer)
- By tearing out the page and rewriting the entry on a new page
Correct answer: By drawing a single line through the error, initialing, dating, and writing the correction
GLP requires that errors be crossed out with a single line so the original entry remains legible, then initialed, dated, and corrected.
Question 3: When centrifuging samples, what is the most important safety consideration regarding tube placement?
- All tubes must be filled to the same volume for accurate results
- Tubes must be balanced in the rotor to prevent vibration and potential rotor failure (Correct answer)
- Only polypropylene tubes should be used in centrifuges
- The centrifuge must be placed in a biosafety cabinet
Correct answer: Tubes must be balanced in the rotor to prevent vibration and potential rotor failure
Unbalanced rotors create dangerous vibrations that can cause catastrophic rotor failure and release of aerosols or hazardous materials.
Question 4: A laboratory technician is asked to validate a new analytical method. Which parameter assesses how close the measured value is to the true value?
- Precision
- Accuracy (Correct answer)
- Linearity
- Robustness
Correct answer: Accuracy
Accuracy measures the closeness of a result to the true or accepted reference value, while precision measures reproducibility.
Question 5: What does the term 'chain of custody' refer to in a laboratory context?
- The hierarchy of laboratory management responsible for sample integrity
- The documented record of who handled a sample and all transfers, storage, and processes it underwent (Correct answer)
- The sequence of chemical reactions performed on a sample
- The order in which samples are processed in a batch
Correct answer: The documented record of who handled a sample and all transfers, storage, and processes it underwent
Chain of custody is the chronological documentation that tracks possession, handling, and location of a sample to ensure its integrity and admissibility.
Question 6: Which autoclave cycle parameter is most critical for achieving sterilization of a liquid media load?
- Pressure only, regardless of temperature
- Temperature held at 121°C for sufficient time (typically 15–20 minutes) (Correct answer)
- The drying phase at the end of the cycle
- The pre-vacuum phase at the beginning of the cycle
Correct answer: Temperature held at 121°C for sufficient time (typically 15–20 minutes)
Sterilization requires maintaining 121°C (at 15 psi) for at least 15 minutes to ensure complete destruction of microorganisms including spores.
Question 7: A researcher obtains an R² value of 0.998 for a standard curve. What does this indicate?
- There is a 0.2% error in every measurement
- The linear relationship between concentration and signal is very strong (Correct answer)
- Only 99.8% of samples were analyzed correctly
- The assay has a 99.8% sensitivity
Correct answer: The linear relationship between concentration and signal is very strong
An R² (coefficient of determination) close to 1.000 indicates that the data points fit the linear model very well, confirming a strong linear relationship.
STP Laboratory Practice 3
What is the primary purpose of a fume hood in a chemistry laboratory?