Laboratory Practice Questions for Level 2 · Intermediate

1. Question 1

   An independent thermometer confirms that a stabilized BOD incubator is warming above range. The door seal, air circulation, room temperature, and recent sample loading are normal. Which finding best identifies a control-system cause?

   1. The temperature sensor reads lower than the independent thermometer.
   2. The door-switch input changes state whenever the door opens.
   3. The circulation fan maintains a uniform temperature across the chamber.
   4. The chamber returns to range after the room temperature is lowered.
   Show the answer

   Answer: A. The temperature sensor reads lower than the independent thermometer.

   A temperature sensor reading lower than a verified independent thermometer can cause the controller to under-respond and allow the chamber temperature to rise.

2. Question 2

   Replicate laboratory results agree closely with one another, but their average falls outside the certified reference material's acceptance limits. How should the results be described?

   1. Accurate but imprecise.
   2. Accurate and precise.
   3. Precise but not acceptably accurate.
   4. Neither precision nor accuracy can be evaluated.
   Show the answer

   Answer: C. Precise but not acceptably accurate.

   Close agreement demonstrates precision, while failure of certified acceptance limits shows unacceptable accuracy.

3. Question 3

   Compared with equal-time composite sampling, how does flow-proportional sampling represent periods of high wastewater flow?

   1. It reduces their total contribution by collecting aliquots less often.
   2. It increases their total contribution through aliquot volume or frequency.
   3. It gives every time interval the same contribution regardless of flow.
   4. It excludes high-flow aliquots when the daily total exceeds normal flow.
   Show the answer

   Answer: B. It increases their total contribution through aliquot volume or frequency.

   Weighting the composite by flow better represents the wastewater volume and load over the sampling period.

4. Question 4

   A cleaned pH electrode reads 7.0 in fresh pH 7 buffer and 8.6 in fresh pH 10 buffer after stabilization at controlled temperature. Which calibration pattern is present?

   1. A compressed slope with an acceptable neutral point.
   2. A uniform positive offset at both calibration points.
   3. An expanded slope with an acceptable neutral point.
   4. A uniform negative offset at both calibration points.
   Show the answer

   Answer: A. A compressed slope with an acceptable neutral point.

   A correct zero point with a compressed response at the second buffer indicates poor slope/span.

5. Question 5

   What is the main purpose of a chain-of-custody record for a compliance sample?

   1. Document who controlled the sample from collection through analysis.
   2. Calculate the pollutant loading represented by the sample.
   3. Select the analytical method used for every permit parameter.
   4. Replace preservation and holding-time requirements for the sample.
   Show the answer

   Answer: A. Document who controlled the sample from collection through analysis.

   Chain-of-custody documentation records sample possession and transfers, supporting sample identity and defensibility.

Operator Master has 20 Level 2 · Intermediate laboratory questions, free.

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